The max position size calculator outputs the largest trade you can take while keeping total account risk at or below a fixed percentage of equity. The core formula — Position Size = (Account × Risk%) ÷ (Entry − Stop) — is simple, but most traders calculate it incorrectly or skip it entirely. The calculator above provides instant results for stocks, futures, and forex so there is no manual arithmetic between idea and execution.
How to Use
| Input | What to Enter | Example |
|---|---|---|
| Account Size | Current account equity in USD | $30,000 |
| Risk Per Trade | Percent of account you accept losing | 1% |
| Entry Price | Your planned entry price | $210.00 |
| Stop Loss Price | Stop loss that caps your loss per unit | $206.50 |
| Asset Class | Stocks, ES Futures, or Forex | Stocks |
The output shows maximum shares or contracts, total dollar risk, and position notional value. If the notional value exceeds available margin, reduce position size or widen stop — never remove the stop.
Formula Explained
Position Size = (Account Size × Risk %) ÷ (Entry Price − Stop Loss Price)
Account Size × Risk % is your maximum dollar risk — the amount you are comfortable losing if the trade goes to stop. At 1% on a $30,000 account, that is $300.
Entry Price − Stop Loss Price is per-unit risk: how much you lose on each share, contract, or lot if stopped out. A $210 entry with a $206.50 stop means $3.50 at risk per share.
Dividing gives the exact unit count: $300 ÷ $3.50 = 85.7 shares, rounded down to 85. Always round down — rounding up increases risk beyond your limit.
Asset class changes the per-unit risk calculation. For ES futures, each point equals $50, so a 6-point stop costs $300 per contract. For EURUSD forex, each pip equals $10 per standard lot, $1 per mini lot, and $0.10 per micro lot.
Example Calculations
Scenario 1: AAPL Stock — $30,000 Account, 1% Risk
- Account: $30,000 | Dollar risk: $300
- Entry: $210.00 | Stop: $206.50 | Risk per share: $3.50
- Result: $300 ÷ $3.50 = 85 shares | Position value $17,850 | Actual risk $297.50
A gut-feel decision to buy 100 shares instead puts $350 at risk — 1.17% of equity. That 17% overshoot seems minor in isolation but compounds meaningfully across dozens of trades per month, as documented in Barber and Odean’s research showing over-sizing is a primary driver of retail underperformance.
Scenario 2: ES Futures — $30,000 Account, 1% Risk
- Account: $30,000 | Dollar risk: $300
- Entry: 5,250 | Stop: 5,244 | Stop distance: 6 points × $50 = $300 per contract
- Result: $300 ÷ $300 = 1 contract | Notional exposure ~$262,500
One ES contract with a 10-point stop costs $500. If your dollar risk is $300, the correct answer is zero contracts for that wider stop — not one. The calculator surfaces this constraint immediately rather than after the loss.
Scenario 3: EURUSD Forex — $10,000 Account, 1% Risk
- Account: $10,000 | Dollar risk: $100
- Entry: 1.0850 | Stop: 1.0830 | Stop distance: 20 pips
- Risk per mini lot: 20 × $1 = $20
- Result: $100 ÷ $20 = 5 mini lots | Actual risk exactly $100
Micro lots ($0.10/pip) allow precise sizing on accounts under $10,000 where rounding to the nearest mini lot can distort risk by 15–25%.
When to Use This Calculator
- Before every trade entry: position size should be the last number confirmed before execution, not the first assumption made when the idea forms.
- When using ATR-based stops: volatility-adjusted stops change per-unit risk on every trade, making manual calculation unreliable.
- After an account drawdown: a 10% drawdown on a $30,000 account reduces dollar risk at 1% from $300 to $270 — sizing must reset to the new equity level.
- Prop firm trading: FTMO and Topstep enforce both a per-trade limit (typically 1–2%) and a daily drawdown ceiling (4–5%). Back-calculate position size from the binding constraint — whichever limit would be hit first with a smaller position governs.
- Evaluating a new strategy: running the calculator backward from a historical stop distance shows whether a strategy is even tradeable at your account size without violating risk rules.
Related Tools
- Position Size Calculator — General-purpose position sizer that accepts custom contract multipliers for any instrument.
- Risk Per Trade Calculator — Determine optimal dollar risk per trade from account size, win rate, and expected drawdown tolerance.
- Kelly Criterion Calculator — Calculates the theoretically optimal risk fraction (approx. 16.7% for a 55% win-rate, 1.5:1 RR system); most traders use half-Kelly (8%) as a conservative ceiling.
- Stop Loss Calculator — Set stop prices from ATR multiples or fixed dollar risk, then feed the result directly into this calculator.
- Lot Size Calculator — Forex-specific sizing tool with pip value tables for major and minor pairs.
Frequently Asked Questions
What is the max position size formula for stocks?
Max position size for stocks equals your dollar risk divided by risk per share. Dollar risk = Account Size × Risk %. Risk per share = Entry Price − Stop Loss Price. For a $25,000 account risking 2% with a $3 stop, that is $500 ÷ $3 = 166 shares (rounded down).
How do I calculate max position size for futures?
For ES futures, each point is worth $50. Divide your dollar risk by (stop distance in points × $50). A $500 risk limit with a 10-point stop gives $500 ÷ ($50 × 10) = 1 contract. For other contracts, substitute the correct point value — NQ is $20/point, MES (micro ES) is $5/point.
Why should position size change as my account grows?
Fixed-share sizing locks risk at the wrong level as equity changes. Losing $200 on a $10,000 account at a $2 stop is 2% of capital. On a $50,000 account the same 100-share trade is only 0.4% — systematically under-risking capital that could be working harder. Percentage-based sizing scales exposure correctly in both directions.
What risk percentage do professional traders and prop firms use?
Most professional traders and prop firms cap single-trade risk at 0.5–2% of equity. Firms like FTMO and Topstep publish rules requiring no more than 1–2% risk per trade and a 4–5% maximum daily drawdown, so each trade must satisfy both constraints simultaneously — take the smaller position.
How does ATR affect position size calculations?
ATR-based stops set stop distance proportional to recent volatility, meaning risk per share varies with each setup. A 1.5× ATR stop on a stock with a $4 ATR creates a $6 stop; on a $2 ATR day it is $3. The position size must be recalculated fresh for every trade — a static share count fails as soon as volatility shifts.
