How to Calculate Risk Per Trade for Forex EAs (Position Sizing)

Instruções passo a passo

1. Passo 1: Understand fixed-fractional sizing

   Fixed-fractional position sizing risks a constant percentage of equity per trade. As the account grows, lot sizes scale up; as the account drawdowns, lot sizes scale down. This is mathematically optimal for capital preservation over long horizons and is what every professional risk-management framework uses.

   The alternative — fixed-lot sizing — risks a constant dollar amount regardless of equity. For a $1000 account trading 0.1 lot, a 100-pip loss is $100 = 10% of equity. After three losses you're at $700 still trading 0.1 lot — but now that 0.1 lot represents 14% per loss instead of 10%. Drawdowns compound destructively.

   Fixed-fractional inverts this: after losses, lot sizes decrease, so each subsequent loss is the same percentage of the (now smaller) equity. The drawdown stays bounded.

   The one downside of fixed-fractional: recovery from drawdown is slower than with fixed-lot, because you're trading smaller lots on the way back up. Trade-off for capital preservation.

2. Passo 2: The formula

   Lot Size = (Account Equity × Risk Percent) / (Stop Loss in Pips × Pip Value per Lot)

   Breaking down each input:

   • Account Equity — read from MT5's Account window. Use current equity (mark-to-market), not balance. If you have open positions, equity already reflects unrealized P&L.

   • Risk Percent — the percentage of equity you're willing to lose on this single trade. Standard retail: 1%. Conservative: 0.5%. Aggressive: 2%. Prop firms: 0.5% to stay safely under daily-loss limits.

   • Stop Loss in Pips — the distance from entry to stop loss, in pips. For EURUSD at 1.0850 with stop at 1.0820, that's 30 pips.

   • Pip Value per Lot — the dollar value of a 1-pip move on a 1.0 lot position. Symbol-specific (see next step).

   Worked example: $5000 equity, 1% risk, 40-pip stop on EURUSD with $10/pip pip value. Lot Size = ($5000 × 0.01) / (40 × $10) = $50 / $400 = 0.125 lots

   MT5 only accepts lot sizes in increments of 0.01, so round to 0.12 lot. The actual risk becomes 0.12 × 40 × $10 = $48 = 0.96% of equity. Close enough to the 1% target.

3. Passo 3: Pip value by symbol

   Pip value is per 1.0 standard lot (100,000 units of the base currency). For account currency = USD:

   • EURUSD, GBPUSD, AUDUSD, NZDUSD — $10/pip. (USD is the quote currency, pip = 0.0001, so 0.0001 × 100,000 = $10.)

   • USDJPY, USDCHF, USDCAD — pip is 0.01 (JPY) or 0.0001 (CHF, CAD), but USD is the base, so pip value varies with the current rate. At USDJPY 150, pip value ≈ $6.67. At USDJPY 100, pip value ≈ $10. For practical EA sizing, look up current pip value in MT5's market info or use our pip-value calculator.

   • EURGBP — pip is 0.0001 in GBP. At GBPUSD 1.27, pip value ≈ $12.70 per lot. Updates with GBPUSD.

   • XAUUSD (Gold) — pip is 0.01 (1 cent). Pip value = $1/pip per standard lot. So a 50-pip move on 0.10 lot of gold = 50 × $1 × 0.10 = $5. Many traders incorrectly treat gold pip as $10/lot like EURUSD; this overestimates risk 10×.

   • BTCUSD — pip is 0.01 to 1.00 depending on broker convention. Check the broker's symbol specification.

   For a non-USD account currency, multiply pip value by the conversion rate. EUR account holding EURUSD: pip value is €(10 / EURUSD_rate). MT5's Market Watch → Symbols → Properties shows the broker's pip value in account currency.

4. Passo 4: Map the formula to your EA's inputs

   Most EAs expose either a fixed LotSize input or a RiskPercent input. Use RiskPercent if available — it implements fixed-fractional automatically.

   If the EA only exposes a fixed LotSize: 1. Compute the right lot size for your current equity using the formula above. 2. Set the LotSize input to that value. 3. Recompute and update every time your equity changes by 20%+. This is manual but necessary.

   If the EA exposes both LotSize and RiskPercent, RiskPercent usually takes precedence and overrides LotSize. Check the EA's documentation.

   If the EA exposes a 'LotSizeMode' choice (Fixed / Percent / Money-Per-Trade), choose Percent.

   A few EAs require Money-Per-Trade — you tell the EA 'risk $50 per trade'. Compute manually: $5000 × 1% = $50.

   For multi-symbol EAs, ensure the RiskPercent setting is per-trade, not per-day. Some EAs interpret 1% as 'no more than 1% loss per day total' rather than 'per trade' — read the docs.

5. Passo 5: Correlate risk across multiple EAs

   If you run 5 EAs each at 1% risk, your worst-case daily loss is not 1% — it's potentially 5% if all five lose on the same day. For correlated EAs (e.g. two scalpers on EURUSD), losses are highly correlated and tend to cluster.

   The right approach: • Compute the EA's correlation matrix from historical trade timestamps. • Set per-EA risk to (Target Total Risk) / sqrt(N) for uncorrelated EAs, or (Target Total Risk) / N for correlated EAs.

   For a target of 1% total daily risk: • 1 EA → 1% per EA • 2 uncorrelated EAs → 0.7% each (1% / sqrt(2)) • 5 uncorrelated EAs → 0.45% each (1% / sqrt(5)) • 5 correlated EAs (all EURUSD scalpers) → 0.2% each (1% / 5)

   In practice, most EA portfolios are 30–70% correlated, so use the per-EA risk formula 1% / sqrt(N × 1.5) as a heuristic. For 5 EAs: 1% / sqrt(7.5) = 0.37%.

6. Passo 6: Set a drawdown budget separately from per-trade risk

   Per-trade risk and account-level drawdown budget are separate parameters. A 1% per-trade risk allows for ~20% drawdown before triggering most psychological/regulatory limits; a 0.5% per-trade risk allows for ~10% drawdown.

   Define your hard drawdown stop in advance: • Personal account — when account drawdown hits -15% from peak, stop the EAs and review. • Prop firm challenge — stop EAs at 70% of the firm's max drawdown rule (e.g. 7% out of 10% allowed) to leave margin for the final closing. • Demo account — no need for hard limit; drawdown is data, not pain.

   Commit to the limit in writing. If you hit it, stop trading the EA until you investigate why. The most common cause is regime change (the market entered conditions the EA wasn't tuned for); the cure is parameter re-tuning, not raising the stop and hoping.

   MT5 has built-in 'Max equity drawdown' settings in some EAs. Use them as a safety net but don't rely on them — the EA developer's max-DD logic isn't always what you want.

Erros comuns a evitar

• ✗ Using fixed lot size regardless of account equitySolução: Switch to RiskPercent input on the EA. As equity changes, lot size auto-adjusts.
• ✗ Mis-calculating XAUUSD pip value as $10/lot (it's $1/lot)Solução: Gold's pip is 0.01 (1 cent), so 1 lot moves $1 per pip. Don't apply the EURUSD pip value to gold.
• ✗ Setting 1% risk per EA when running 5 EAsSolução: Total risk is what matters. Scale per-EA risk down so combined exposure stays at target.
• ✗ Confusing risk percent with leverage percentSolução: Risk % is potential loss; leverage % is position size. Risking 1% of equity on a 40-pip stop is about 25% effective leverage on a $5000 account at 1:30 broker leverage.
• ✗ Recomputing position size monthly instead of per tradeSolução: If the EA reads account equity dynamically (recommended), it sizes correctly automatically. If you set lot manually, recompute before every session, not monthly.
• ✗ Treating prop-firm risk rules as the same as personal risk rulesSolução: Prop firms have hard daily-loss limits (often 5%) that you cannot exceed even momentarily. Size at 0.5% per trade so daily total stays well under the limit.

Perguntas frequentes