AlamToolKit · Trading Risk Tools
Position Size Mistake Calculator / Simulator
A standard position size calculator tells you the correct size. This one tells you what your mistake actually cost you: enter what you meant to risk and the size you really entered, and see the real risk in cash, as a percentage of your account, as a multiple of your plan, and what one extra zero can do.
Trade setup: account and instrument
Modes C and D reveal the extra comparison inputs below.
Presets load contract size, tick size and tick value. Edit them if your broker differs.
Sizing off balance while you have open drawdown overstates your true capacity.
Used as the risk base, unless mode D or the advanced override is used.
Used to validate that the stop sits on the correct side of entry.
Prices and stop distance
Distance is derived automatically: |entry − stop|.
Unit sizes come from the instrument preset and are editable in the advanced panel.
Your risk plan and the size you entered
Leave blank and the tool computes the size that fits your risk plan, then compares it with the size you entered.
The number you really typed into your platform.
Mistake presets — apply a multiplier to the base size
Advanced: contract specs, costs, leverage and limits
Contract specification (what one “lot” really is)
A lot means 100,000 units in forex, 100 oz in gold, 1 contract in ES futures and something else entirely on a CFD broker. Wrong specs make every number below wrong.
Only needed when the instrument’s profit currency differs from your account currency (example: trading EUR/GBP on a USD account). Leave at 1 otherwise.
Trading costs, slippage and spread
Microcopy: never count the spread twice — if you already entered a realistic fill price for entry or stop, set the spread to 0.
Leverage, existing risk and rule limits
Margin tells you what capital is tied up — it never tells you what you can lose. A trade can be affordable on margin and still be account-threatening.
Extra comparison inputs (modes C and D)
These let the tool attribute the mistake to the right cause: the size, the stop distance or the balance.
Damage report: intended risk vs actual risk
Enter your numbers to see the comparison.
Headline numbers
Intended vs actual, side by side
| Line item | Your plan | What you did | Difference |
|---|---|---|---|
| Position size | — | — | — |
| Stop distance | — | — | — |
| Risk at the stop | — | — | — |
| Risk as % of account | — | — | — |
| Trading costs included | — | — | — |
| Notional exposure | — | — | — |
| Margin required | — | — | — |
| Equity after the stop | — | — | — |
The correction
Diagnosis: where the mismatch came from
Waiting for inputs.
Warnings and checks
- No checks run yet.
Details and assumptions used
- —
Accuracy note: results are an estimate built from the numbers and contract specification you provide. The tool assumes the stop is filled at the price you entered, that the contract specification stays correct for the life of the trade, and that your account has no other exposure unless you entered it. Real fills, gaps, partial fills and liquidation can all change the outcome, so treat the loss figure as a planned estimate, not a guarantee.
Off by default: your balance and position sizes are private.
Scenario: what the trade sequence looks like
Randomized modes run many paths and are clearly labelled as simulations, never predictions.
Used to generate randomized paths. With your own sequence, the list length wins.
Use 1.1 if your stops routinely slip — a loss bigger than 1R is normal, not a mistake.
Comma, space or newline separated. Examples: W W L L W or -1, +2, -1, -1, +1.5. A bare W means “won the average win”; L means “lost the average loss”.
The mistake: what is entered wrongly, and how often
Error type
10× means the error trade risks ten times the planned amount.
Charged on both scenarios so the comparison stays fair.
A path is counted as ruined if equity falls below this level.
Equity paths: correct sizing vs mistaken sizing
Mode: user-defined sequence
The mistake cost card
Total difference caused by sizing errors alone (same trades, same strategy)
Randomized-mode statistics
Percentile fan: mistake scenario (5th / 25th / 50th / 75th / 95th)
Distribution of final balances, mistake scenario
Trade-by-trade path
| # | Outcome (R) | Correct equity | Mistake equity | Error |
|---|
Every formula this calculator uses
Each formula below is applied exactly as written, in the order shown. Where an assumption is required it is stated next to the formula.
Loss per size unit at the stop
Price distance from entry to stop:
\[ d = \left| P_{e} - P_{s} \right| \]Cash lost per one size unit (one lot, one contract, one share) when the stop is hit, converted into the account currency:
\[ L_{u} = d \times C \times k \]\( C \) = contract size (units per lot or multiplier per contract), \( k \) = quote-to-account conversion rate. For a plain share trade, \( C = 1 \) and \( k = 1 \), so \( L_u = d \).
Risk budget from the plan
Percentage mode, applied to the chosen risk base \( E \) (balance or equity):
\[ R_{i} = E \times r \]Fixed-amount mode: \( R_i \) is used directly. If both are supplied, the tool reports whether they agree.
Intended risk, actual risk and the overshoot
When the intended and actual stop distances differ, each side uses its own distance; when the contract size differs, each side uses its own specification:
\[ R_{\text{intended}} = Q_{i} \, d_{i} \, C_{i} \, k \qquad\qquad R_{\text{actual}} = Q_{a} \, d_{a} \, C_{a} \, k \]Cash overshoot, overshoot percentage and the risk multiple:
\[ \Delta R = R_{\text{actual}} - R_{\text{intended}} \] \[ \text{Overshoot \%} = \frac{\Delta R}{R_{\text{intended}}} \times 100 \qquad\qquad M = \frac{R_{\text{actual}}}{R_{\text{intended}}} \]If \( R_{\text{intended}} = 0 \) the tool must not divide by zero: it reports “risk multiple unavailable” instead of an infinite number.
Risk as a share of the account, and the damage at the stop
The gain needed on the remaining equity to get back to where you started:
\[ \text{Recovery} = \frac{\text{loss \%}}{1 - \text{loss \%}} \]The correct position size
Raw size that exactly spends the risk budget, including per-unit costs \( c_u \) when costs are switched on:
\[ Q_{\text{raw}} = \frac{R_{i}}{L_{u} + c_{u}} \]Rounded down to the broker’s quantity increment \( s \):
\[ Q_{\text{valid}} = \left\lfloor \frac{Q_{\text{raw}}}{s} \right\rfloor s \]If \( Q_{\text{valid}} \) is below the broker minimum, the honest answer is “too small to size correctly at this risk” — not a forced minimum with double the risk. The tool warns instead of rounding up.
Costs
Do not count the spread twice. If the entry or stop price you entered is already a realistic fill, set the spread to zero.
Notional and margin
Margin is what your broker ties up. It is not your maximum loss. A trade can be affordable on margin and still be account-threatening.
Scale-out of the pipelines in words
1. Read the intended risk \(R_i\) from your plan. 2. Compute the loss per unit \(L_u\) from the contract specification. 3. Compute the risk of the size you actually entered, \(R_{\text{actual}}\). 4. Divide one by the other to get the multiple. 5. Compare both against the account to get the percentages. 6. Recompute the size that fits the budget, round it down to the lot step, and flag anything that breaks a rule.
Simulator equity update
Compounding (percentage) sizing, with \( x_t \) the trade outcome in R units and \( f \) the fraction risked:
\[ E_{t+1} = E_{t}\left(1 + f x_{t} - c_{R}\right) \]Fixed-cash sizing, with \( R_{\text{cash}} \) the cash risked per trade:
\[ E_{t+1} = E_{t} + R_{\text{cash}} x_{t} - R_{\text{cash}} c_{R} \]On an error trade, replace \( f \) with \( f \times m \) (or \( R_{\text{cash}} \) with \( R_{\text{cash}} \times m \)), where \( m \) is the error multiplier. Both scenarios run over the same \( x_t \) sequence.
Drawdown, streaks and expectancy
The growth formula \(g\) is the quiet lesson: a system with positive expectancy can still shrink for ever once \(f\) is oversized — the same edge fails under a sizing error.
Worked example, start to finish
| Input | Value | Why it matters |
|---|---|---|
| Account balance | 10,000 USD | The risk base |
| Intended risk | 1.0% | Risk budget = 100 USD |
| Entry / stop | 1.08500 / 1.08000 | 50 pips = 0.0050 price distance |
| Contract size | 100,000 units | 1 pip ≈ 10 USD per standard lot |
| Intended size | 0.10 lots | 0.10 × 500 = 50 USD — actually only 0.5% of the account |
| Correct size | 0.20 lots | 0.20 × 500 = 100 USD = the 1% budget, exactly |
| Actual size | 1.00 lot | 1.00 × 500 = 1,000 USD = 10.0% of the account |
| Multiple of plan | 10× | 1,000 / 100 = 10.0× the intended risk |
| Extra cash at risk | +900 USD | 1,000 − 100 = 900 USD more than planned |
| Equity after the stop | 9,000 USD | A 10.0% account loss, not a scratch |
| Recovery needed | +11.1% | 0.10 / (1 − 0.10). The 1% trade needed only +1.01% |
| Expected mistakes in 50 trades | 10 | At a 20% per-trade error rate: 1 − 0.850 ' 100% chance of at least one |
Notice the trap inside the trap: the trader who thought they were risking 1% with 0.10 lots was really risking 0.5%. They had already lost trust in their own numbers before the extra zero appeared. Nothing here recommends a trade — it returns the arithmetic, the gap and the correction.
Input units, parameters and options
| Category | Units and options |
|---|---|
| Account | Currency selector (USD, EUR, GBP, JPY, CAD, AUD, CHF, INR, BDT, USDT, custom); balance vs equity toggle |
| Instrument | Preloaded contract specs, or manual contract size, tick size, tick value, pip size, lot step, minimum and maximum size |
| Prices | Entry, stop, optional take-profit, in the instrument’s own quote |
| Distance | Pips, points, ticks or price units, converted automatically from the preset |
| Risk | Percentage of account or fixed cash amount; intended and actual |
| Size | Lots, contracts, shares, units, coins or a custom label; rounded down to the step |
| Costs | Commission per lot round turn; spread and slippage in pips, points or price |
| Leverage | Ratio 1:X, used only for the margin comparison |
| Limits | Daily loss limit and maximum drawdown limit, prop-firm style |
| Simulation | Trades, win rate, average win and loss in R, error multiplier, error frequency, fees in R, runs, random seed |
| Thresholds | Drawdown alert percentage and ruin threshold as a percentage of the starting balance |
Frequently asked questions
- How do I calculate risk per trade?
- Decide the cash you are willing to lose if the stop is hit (usually a percentage of your balance or equity). Divide that amount by the cash lost per size unit, which is the price distance from entry to stop multiplied by the contract size and any currency conversion. The answer is the maximum size that respects your plan.
- What actually happens if I use the wrong lot size?
- Your risk scales with the error when the stop distance is unchanged. Ten times the size is ten times the cash at risk, so a 0.5% plan becomes a 5% trade and the number of consecutive losses you can survive drops by the same factor.
- Is 1.00 lot instead of 0.10 lot really ten times the risk?
- Yes, if the instrument, the stop distance and the account are unchanged. Change any of the three and the multiple changes with it — which is why the tool recalculates instead of labelling every decimal slip as “10×”. It reports a possible cause, never a certain one.
- My broker shows the margin is affordable — isn’t that enough?
- No. Margin is the capital tied up by the position; risk is what you lose if the stop is hit. They are different numbers and the tool shows them side by side so the gap is visible.
- Why does my loss sometimes exceed the number this tool shows?
- Because the stop is an order, not a promise. Gaps, weekend gaps, thin liquidity, slippage and widening spreads can all fill you further away than the stop price. That is what the slippage allowance is for: it shows your realistic worst case alongside the plan.
- What if the correct size is smaller than my broker’s minimum?
- Then the trade cannot be sized correctly on this account at this risk. The honest answers are a wider account, a tighter stop, or a smaller risk base — not forcing the minimum lot and quietly doubling your exposure.
- Is the simulator a prediction of my account?
- No. It is a model. Randomized runs shuffle outcomes, which removes the clustering of losses that real markets produce, so they can look gentler than reality. Every chart is labelled with its mode and the results belong to that sequence and that model only.
Work out the rest of your risk plan
This page exists to quantify a mistake. These tools cover the intent that comes next — planning the trade properly, then surviving it.
AlamToolKit · Trading Risk Tools
Position Size Mistake Calculator / Simulator — User Guide & Results Explained
A complete walkthrough of the Position Size Mistake Calculator: what every field means, how the results are calculated, which units apply, how inputs are validated, and what the numbers can — and cannot — tell you. Use this guide alongside the live calculator to turn a sizing error into a measurable, fixable number.
What Is This Calculation Used For?
A standard position size calculator tells you the correct size. This tool tells you what your mistake actually cost you: enter what you meant to risk and the size you really entered, and see the real risk in cash, as a percentage of your account, as a multiple of your plan, and what one extra zero can do to your equity.
It is built for traders who already have a risk plan — typically 1% of account per trade — but who occasionally enter the wrong quantity, size on the wrong stop distance, or size on an old balance. The calculator quantifies that error in currency terms and gives you the exact correction.
Who should use it
- Forex, CFD, futures and crypto traders who enter lot sizes or contract counts manually.
- Prop-firm challengers who must never breach a daily or overall loss limit.
- Traders reviewing a closed trade who want to know what the sizing error really cost.
- Risk managers and educators who need a concrete, reproducible number for a case study.
Where traders apply it in the real world
- Post-trade review: reconstruct a trade where the size was wrong and measure the overshoot.
- Pre-trade sanity check: confirm that the lot size you are about to click matches the plan.
- Prop-firm compliance: verify a single trade against a 5% daily loss limit before entry.
- Teaching: show why 1.00 lot instead of 0.10 lot is 10× the risk, not 10% more.
- Journaling: export a PDF or PNG summary card and attach it to the trade journal.
Step-by-Step User Guide
The calculator has three tabs: Mistake Checker, Mistake Simulator and Formulas & Guide. Start with the checker. Every field below is live — results update as you type.
Step 1 — Trade setup: account and instrument
| Field | What it means | Units / options |
|---|---|---|
| What are you checking? | Selects the comparison mode. A compares the entered size with your risk plan. B compares the intended size with the actual size. C handles a wrong stop distance. D handles a wrong balance. Modes C and D reveal extra comparison inputs. | Dropdown: A, B, C, D |
| Instrument preset | Loads the contract size, tick size, tick value, pip size and lot step for a specific market. Every value stays editable, so use your broker’s specification if it differs. | EUR/USD, GBP/USD, USD/JPY, gold, silver, indices, crypto, futures, crude oil, stocks, custom |
| Account currency | The currency your account is denominated in. All cash results are shown in this currency. | USD, EUR, GBP, JPY, CAD, AUD, CHF, INR, BDT, USDT, custom code |
| Risk basis: balance or equity | Whether the plan is calculated on the account balance or on equity (balance plus or minus open P&L). Sizing on balance while you are in drawdown overstates your true capacity. | Balance / Equity |
| Account value | The actual number used as the risk base, in your account currency. | Cash amount (e.g. 10,000.00 USD) |
| Trade direction | Long or short. Used to validate that the stop sits on the correct side of the entry price. | Long / Buy · Short / Sell |
| Size unit | The label for the position size. It only changes how numbers are displayed — the underlying calculation uses the contract size. | Lots, contracts, shares, units, coins, custom |
Common mistake: leaving a lot-based instrument on “custom” with a contract size of 1. A EUR/USD lot is 100,000 units — a contract size of 1 will make the loss look 100,000× too small.
Step 2 — Prices and stop distance
| Field | What it means | Units |
|---|---|---|
| Stop-loss input mode | Choose whether you want to enter the stop as a price (entry + stop price) or as a distance (entry price + stop distance). | Prices / Distance |
| Entry price | The price at which the position was opened. | Price in the instrument’s quote currency |
| Stop-loss price | The price at which the stop order sits. The distance is derived automatically as |entry − stop|. | Price in the instrument’s quote currency |
| Stop distance | Used when the stop is entered as a distance instead of a price. Converted to price units using the pip size or tick size from the preset. | Pips, points, ticks or price units |
| Take-profit price (optional) | If supplied, the calculator shows the reward-to-risk multiple (R:R) of the trade. | Price in the instrument’s quote currency |
Common mistake: entering a stop above the entry price on a long, or below it on a short. The calculator flags this as a validation error — but it cannot know whether your direction or your stop price is wrong.
Step 3 — Your risk plan and the size you entered
| Field | What it means | Units / options |
|---|---|---|
| Intended risk is stated as | Whether your plan is a percentage of the account or a fixed cash amount. | Percentage / Fixed cash |
| Intended risk (% of account) | The fraction of the risk base you were willing to lose if the stop hit. Typical values are 0.5% to 2%. | Percent (e.g. 1.0%) |
| Intended risk (cash amount) | Used when the plan is stated as a fixed sum rather than a percentage. | Cash in account currency |
| Intended position size | The size your plan called for. Leave it blank and the calculator computes the size that fits your risk plan, then compares it with the size you entered. | Lots / contracts / shares / units / coins |
| Actual / mistaken position size | The number you really typed into your platform. This is the error side of the comparison. | Lots / contracts / shares / units / coins |
| Mistake presets ×0.1 … ×100 | Multiplies the base size by a preset factor and writes the result into the actual-size field. Useful for quickly modelling “one extra zero” (×10) or “a decimal shift” (×0.1). | Buttons |
| Custom multiplier | Applies any multiplier you type to the base size. | Any positive number |
Common mistake: leaving the intended size blank and then assuming the calculator used the number you typed in the actual field. If the intended size is blank, it is auto-calculated from the risk plan — check the “Your plan” column in the comparison table.
Step 4 — Advanced: contract specs, costs, leverage and limits
The advanced panel is collapsed by default. Open it when your broker’s specification differs from the preset, when you want costs included, or when you are checking a prop-firm rule.
Contract specification
| Field | What it means | Units |
|---|---|---|
| Contract size (units per lot) | How many units of the underlying one “lot” or one “contract” represents. Forex: 100,000. Gold: 100 oz. ES futures: 50. | Units per lot |
| Tick size (price units) | The smallest price increment the instrument can move. | Price units (e.g. 0.00001) |
| Tick value (account currency per lot) | The cash value of one tick for one lot, in the account currency. Used for cross-checks and for instruments quoted in another currency. | Cash per tick per lot |
| Pip size (price units) | One pip measured in price units. EUR/USD: 0.0001. USD/JPY: 0.01. | Price units |
| Quantity step (lot step) | The smallest increment your broker accepts. Sizes are rounded down to this step, never up. | Size units (e.g. 0.01) |
| Minimum size | The smallest trade your broker will accept. | Size units |
| Maximum size (0 = no limit) | A cap used only for validation warnings. | Size units |
| Quote→account conversion rate | Needed when the instrument’s profit currency differs from your account currency — for example EUR/GBP on a USD account. Leave at 1 otherwise. | Ratio (e.g. 1.27) |
Trading costs, slippage and spread
| Field | What it means | Units |
|---|---|---|
| Include commission, spread and slippage | When checked, costs are added to the price-move risk on both the plan and the actual side. | Checkbox |
| Commission per lot, round turn | Total commission charged to open and close one lot. | Cash per lot |
| Spread | The bid-ask spread you expect to pay. If your entry or stop price is already a realistic fill, set this to 0 to avoid double-counting. | Pips, points or price |
| Stop slippage allowance | An extra distance the stop might fill beyond its price — gaps, thin liquidity, weekend opens. Shown separately as the “worst case” figure. | Pips, points, ticks or price |
Leverage, existing risk and rule limits
| Field | What it means | Units |
|---|---|---|
| Leverage (1:X) | Used only for the margin comparison. Margin is what your broker ties up; it is not your maximum loss. | Ratio (e.g. 100) |
| Existing open risk (cash) | Risk already committed on other open trades. Added to the trade risk to show total committed risk. | Cash |
| Daily loss limit (%) | Prop-firm or personal daily limit. The calculator warns if a single trade already breaches it. | Percent of account |
| Max drawdown limit (%) | Overall drawdown allowance. Same warning logic. | Percent of account |
| Trade status | Labels the report: hypothetical, pending order, open trade or closed trade. | Dropdown |
| Trade date | Optional date stored in the report. | Date |
Common mistake: treating an “affordable” margin requirement as proof the trade is safe. A 1.00 lot EUR/USD trade at 1:100 leverage needs about 1,085 USD of margin — but its stop-loss loss can be ten times the planned risk. Margin ≠ risk.
Step 5 — Reading the damage report
The results section answers four questions at a glance:
- What did I plan to risk? — the “Intended risk” KPI in cash and as a percentage.
- What did I actually risk? — the “Actual risk” KPI in cash and as a percentage.
- How big is the multiple? — “Multiple of plan” shows 10× for a one-extra-zero mistake, 2× for a doubled size, and so on.
- What does it cost me? — “Extra cash at risk”, “Equity after stop” and “Gain needed to recover”.
Intended vs actual bars
Two horizontal bars visualise the plan and the mistake on the same scale. The bar length is the risk as a percentage of the account, so a 1% plan and a 10% mistake are immediately comparable.
The comparison table
Eight line items are compared side by side: position size, stop distance, risk at the stop, risk as % of account, trading costs, notional exposure, margin required and equity after the stop. The “Difference” column shows the gap in the same units.
The correction
This block gives the correct size — raw and rounded down to your lot step — and the cash risk that size produces. If the correct raw size is below your broker’s minimum, it says so instead of rounding up.
Diagnosis: where the mismatch came from
The calculator labels the possible cause of the overshoot: one extra zero, a units-vs-lots confusion, a doubled size, a wrong stop distance or a stale balance. It is explicitly framed as a possible cause, never a certain one — the tool cannot know what you intended.
Warnings and checks
Inputs are validated in real time. Warnings are separated into danger and caution, and cover: zero account, zero contract size, zero stop distance, wrong-side stops, size below broker minimum, size not a multiple of the lot step, rounding loss above 15% of the budget, account-threatening risk above 5% or 10%, and prop-firm rule breaches.
Details and assumptions used
A bullet list restates every number and assumption behind the result: the risk base, the loss per unit, the cash per pip, the rounding step and the stop-fill assumption. This is the audit trail you can paste into a journal.
Export and share
- Copy full report — plain-text report to clipboard.
- Create shareable link — encodes the inputs in the URL hash. Account balance and sizes are excluded unless you tick the “include my account value” box.
- Download summary card (PNG) — a 1200×700 share card with the headline numbers.
- Print / save as PDF — print stylesheet hides the tabs and controls, leaving a clean report.
- Save this scenario — stores the full input set in your browser’s local storage.
Step 6 — Using the Mistake Simulator
The checker answers “how bad was this one mistake?”. The simulator answers “if I keep making it, what happens to my equity?”. Both curves use the same trade outcomes; only the sizing differs.
| Field | What it means | Units / options |
|---|---|---|
| Simulation mode | User-defined sequence replays your own list in order. Randomized (win rate + average R) generates many parametric paths. Randomized (bootstrap) resamples from your list. | Dropdown |
| Starting balance | Equity at trade 1. | Cash |
| Number of trades | Path length for randomized modes. With a user sequence, the list length wins. | Integer 2–5000 |
| Correct risk per trade | Percentage of current equity (compounding) or a fixed cash amount per trade. | Percent / Cash |
| Win rate (%) | Used for randomized modes and for the expectancy figure. | Percent 0–100 |
| Average win (R) | The size of an average winner in risk multiples. | R multiples |
| Average loss (R) | The size of an average loser. Use 1.1 if stops routinely slip. | R multiples |
| Your trade outcomes | Comma, space or newline separated. W = average win, L = average loss, or numeric R multiples such as +2, -1, +1.5. | Text |
| Error type | Oversized quantity, wrong stop distance, or wrong balance used. Changes the tooltip and the report label. | Buttons |
| Error multiplier | How many times the planned risk the error trade takes. 10× is the classic one-extra-zero. | Ratio |
| How often does it happen? | Every N trades, a probability per trade, only on specific trade numbers, or on every trade. | Dropdown + value |
| Fees and slippage per trade (R) | Charged on both scenarios so the comparison stays fair. | R multiples |
| Drawdown alert threshold (%) | Equity drawdown level that triggers an alert marker. | Percent |
| Ruin threshold (% of starting balance) | A path is counted as ruined if equity falls below this level. | Percent |
| Randomized simulation runs | Number of Monte Carlo paths. More runs = smoother statistics, slower to compute. | Integer 100–20000 |
| Random seed | Fixes the random number generator so the same seed reproduces the same results. | Integer |
| Stop a path if equity is wiped out | Caps a path’s loss at the remaining balance instead of letting equity go negative. | Checkbox |
Honest limits, stated up front: randomized runs shuffle trade outcomes, which removes the clustering of losses that real markets produce. Parametric runs assume independent trades, a stable win rate and a stable R-distribution. Gaps, partial fills, liquidity and funding costs are not modelled. Simulated results are not predictions.
Results Calculations — Every Formula Explained
Each formula below is applied exactly as written, in the order shown. Where an assumption is required, it is stated next to the formula.
Loss per size unit at the stop
Price distance from entry to stop:
d = |Pe − Ps|
Cash lost per one size unit when the stop is hit, converted into the account currency:
Lu = d × C × k
C = contract size (units per lot or multiplier per contract), k = quote-to-account conversion rate. For a plain share trade, C = 1 and k = 1, so Lu = d.
Risk budget from the plan
Percentage mode, applied to the chosen risk base E (balance or equity):
Ri = E × r
Fixed-amount mode: Ri is used directly. If both are supplied, the tool reports whether they agree.
Intended risk, actual risk and the overshoot
Rintended = Qi × Lu
Ractual = Qa × Lu
When the intended and actual stop distances differ, each side uses its own distance:
Rintended = Qi × di × Ci × k
Ractual = Qa × da × Ca × k
Cash overshoot, overshoot percentage and the risk multiple:
ΔR = Ractual − Rintended
Overshoot % = (ΔR ÷ Rintended) × 100
M = Ractual ÷ Rintended
If Rintended = 0 the tool reports “risk multiple unavailable” instead of dividing by zero.
Risk as a share of the account, and the damage at the stop
Actual risk % = (Ractual ÷ E) × 100
Eafter stop = E − Ractual
The gain needed on the remaining equity to get back to where you started:
Recovery = loss % ÷ (1 − loss %)
A 10% loss needs a 10 ÷ 90 = 11.1% gain. A 1% loss needs only 1.01%.
The correct position size
Raw size that exactly spends the risk budget, including per-unit costs cu when costs are switched on:
Qraw = Ri ÷ (Lu + cu)
Rounded down to the broker’s quantity increment s:
Qvalid = ⌊Qraw ÷ s⌋ × s
If Qvalid is below the broker minimum, the tool warns instead of rounding up — forcing the minimum would double the risk.
Costs
Rtotal = Rprice move + Ccommission + Cspread + Cslippage
Ccommission = commission per lot × Q
Cspread = sprice × C × k × Q
Cslippage = σprice × C × k × Q
Do not count the spread twice. If the entry or stop you entered is already a realistic fill, set the spread to zero.
Notional and margin
Notional = Pe × C × Q × k
Margin = Notional ÷ leverage
Margin is what the broker ties up. It is not your maximum loss. A trade can be affordable on margin and still be account-threatening.
Simulator equity update
Compounding (percentage) sizing, with xt the trade outcome in R units and f the fraction risked:
Et+1 = Et × (1 + f × xt − cR)
Fixed-cash sizing, with Rcash the cash risked per trade:
Et+1 = Et + Rcash × xt − Rcash × cR
On an error trade, replace f with f × m, where m is the error multiplier. Both scenarios run over the same xt sequence.
Drawdown, streaks and expectancy
Drawdownt = (maxj≤t Ej − Et) ÷ maxj≤t Ej
MDD = maxt Drawdownt
Expectancy (R) = W × average win − (1 − W) × average loss
g = W × ln(1 + f × average win) + (1 − W) × ln(1 − f × average loss)
P(at least one mistake in N trades) = 1 − (1 − p)N
The growth formula is the quiet lesson: a system with positive expectancy can still shrink forever once f is oversized — the same edge fails under a sizing error.
Worked Example, Start to Finish
Scenario: a trader with a 10,000 USD account on EUR/USD plans to risk 1%, uses a 50-pip stop, and types 1.00 lot instead of 0.10 lot. Here is every number the calculator produces.
| Input / result | Value | Why it matters |
|---|---|---|
| Account balance | 10,000 USD | The risk base |
| Intended risk | 1.0% | Risk budget = 100 USD |
| Entry / stop | 1.08500 / 1.08000 | 50 pips = 0.0050 price distance |
| Contract size | 100,000 units | 1 pip ≈ 10 USD per standard lot |
| Intended size | 0.10 lots | 0.10 × 500 = 50 USD — actually only 0.5% of the account |
| Correct size | 0.20 lots | 0.20 × 500 = 100 USD = the 1% budget, exactly |
| Actual size | 1.00 lot | 1.00 × 500 = 1,000 USD = 10.0% of the account |
| Multiple of plan | 10× | 1,000 ÷ 100 = 10.0× the intended risk |
| Extra cash at risk | +900 USD | 1,000 − 100 = 900 USD more than planned |
| Equity after the stop | 9,000 USD | A 10.0% account loss, not a scratch |
| Recovery needed | +11.1% | 0.10 ÷ (1 − 0.10). The 1% trade needed only +1.01% |
| Expected mistakes in 50 trades | 10 | At a 20% per-trade error rate: 1 − 0.850 ≈ 100% chance of at least one |
Notice the trap inside the trap: the trader who thought they were risking 1% with 0.10 lots was really risking 0.5%. They had already lost trust in their own numbers before the extra zero appeared.
Key User Pain Points and How This Calculator Solves Them
| Pain point | How the calculator solves it |
|---|---|
| “I don’t know what the mistake actually cost me.” | The damage report converts the sizing error into cash, percentage of account, and a multiple of the plan. The “Extra cash at risk” KPI is the direct cost. |
| “My broker says the margin is affordable, so it must be safe.” | Margin and risk are shown side by side. The calculator demonstrates that a trade can be affordable on margin and still risk 10% of the account. |
| “I entered 1.00 instead of 0.10 — is that really 10× the risk?” | Yes, if the instrument, stop distance and account are unchanged. The diagnosis block labels this the classic “one extra zero” signature and shows the exact multiple. |
| “I don’t know which input caused the mismatch.” | The diagnosis block attributes the gap to the size, the stop distance or the balance — using the mode C and D comparison inputs when supplied. |
| “My correct size is below the broker minimum.” | The tool says so explicitly instead of forcing the minimum lot and quietly doubling the risk. |
| “I’m not sure what my contract specification really is.” | Every preset value is editable, and the assumptions list restates the contract size, tick size, pip size and lot step used in the calculation. |
| “I can’t tell if a single trade breaches my prop-firm rules.” | Daily loss limit and max drawdown fields trigger explicit rule-breach warnings when a single trade exceeds them. |
| “I keep making the same mistake.” | The simulator shows the cumulative equity impact of repeating the error, with max drawdown, losing streaks and a Monte Carlo distribution. |
Common Mistakes — Microcopy for Each Field
Size and quantity mistakes
- Leaving the intended size blank: the calculator auto-calculates it. If you meant to use your own number, type it in — otherwise the “Your plan” column is not what you intended.
- Entering units instead of lots: 10,000 units of EUR/USD is 0.10 lots, not 10 lots. Check the size unit selector and the contract size.
- Forgetting the lot step: a raw size of 0.204 lots becomes 0.20 at a 0.01 step. The tool rounds down, never up.
- Typing one extra zero: 0.10 → 1.00 is a 10× risk multiple. Use the ×10 preset to model it instantly.
Stop and price mistakes
- Stop on the wrong side: a long trade’s stop must sit below entry. The calculator flags it, but you must decide whether the direction or the price is wrong.
- Zero stop distance: a stop at the entry price is not a stop. The tool refuses to divide by zero and asks you to move it.
- Counting the spread twice: if your entry price already reflects a realistic fill, set the spread to zero.
- Wrong pip size on JPY pairs: USD/JPY uses a pip size of 0.01, not 0.0001. The preset handles it; a custom instrument may not.
Balance and leverage mistakes
- Sizing on balance while in drawdown: the plan should use current equity. Mode D specifically compares the balance you sized on with the balance you actually have.
- Treating margin as risk: margin is capital tied up, not capital at risk. The comparison table shows both.
- Ignoring existing open risk: the “Existing open risk” field adds other trades to the total committed risk.
Units and currency mistakes
- Forgetting the conversion rate: trading EUR/GBP on a USD account needs a GBP→USD conversion. Leave it at 1 only when the quote currency matches your account currency.
- Custom currency codes: if your currency is not in the list, choose Custom and type the code. The tool falls back to a plain number format if the code is not recognised by the browser.
Accuracy Note — What This Calculator Can and Cannot Do
Results are an estimate built from the numbers and contract specification you provide. The calculator assumes:
- The stop is filled at the price you entered — no gap, no slippage beyond what you explicitly supplied.
- The contract specification stays correct for the life of the trade.
- Your account has no other exposure unless you entered it in the “Existing open risk” field.
- The quote-to-account conversion rate is constant over the trade’s life.
Real fills, gaps, partial fills, spread widening and liquidation can all change the outcome. Treat the loss figure as a planned estimate, not a guarantee. The simulator’s randomized modes are models, not predictions: shuffling trade outcomes removes the clustering of losses that real markets produce, so Monte Carlo can understate risk in a genuinely bad regime.
The calculator is designed to be honest about uncertainty: every assumption is listed in the “Details and assumptions used” section, and every simulation chart is labelled with its mode.
Frequently Asked Questions
- How do I calculate risk per trade?
- Decide the cash you are willing to lose if the stop is hit (usually a percentage of your balance or equity). Divide that amount by the cash lost per size unit, which is the price distance from entry to stop multiplied by the contract size and any currency conversion. The answer is the maximum size that respects your plan.
- What actually happens if I use the wrong lot size?
- Your risk scales with the error when the stop distance is unchanged. Ten times the size is ten times the cash at risk, so a 0.5% plan becomes a 5% trade and the number of consecutive losses you can survive drops by the same factor.
- Is 1.00 lot instead of 0.10 lot really ten times the risk?
- Yes, if the instrument, the stop distance and the account are unchanged. Change any of the three and the multiple changes with it — which is why the tool recalculates instead of labelling every decimal slip as “10×”. It reports a possible cause, never a certain one.
- My broker shows the margin is affordable — isn’t that enough?
- No. Margin is the capital tied up by the position; risk is what you lose if the stop is hit. They are different numbers and the tool shows them side by side so the gap is visible.
- Why does my loss sometimes exceed the number this tool shows?
- Because the stop is an order, not a promise. Gaps, weekend gaps, thin liquidity, slippage and widening spreads can all fill you further away than the stop price. That is what the slippage allowance is for: it shows your realistic worst case alongside the plan.
- What if the correct size is smaller than my broker’s minimum?
- Then the trade cannot be sized correctly on this account at this risk. The honest answers are a wider account, a tighter stop, or a smaller risk base — not forcing the minimum lot and quietly doubling your exposure.
- Is the simulator a prediction of my account?
- No. It is a model. Randomized runs shuffle outcomes, which removes the clustering of losses that real markets produce, so they can look gentler than reality. Every chart is labelled with its mode and the results belong to that sequence and that model only.
- Can I use this for futures, crypto and stocks?
- Yes. Choose the matching preset (ES, NQ, BTC/USD, ETH/USD, stocks) or build a custom instrument with your own contract size, tick size and lot step. For futures, the contract size is the multiplier per contract, not the number of contracts.
- What does “multiple of plan” mean?
- It is the actual risk divided by the intended risk. A multiple of 10× means the trade risks ten times the planned amount. The tool reports “unavailable” when the intended risk is zero, rather than showing an infinite number.
- Where can I share the result?
- Use “Create shareable link” to copy a URL that encodes the inputs in the hash. Account balance and position sizes are excluded unless you tick the “include my account value” box. “Download summary card (PNG)” produces a 1200×700 image for sharing or journaling.
AlamToolKit.com — Position Size Mistake Calculator / Simulator user guide. All calculations are estimates based on the inputs and contract specification supplied. Nothing on this page is investment advice.
