Position sizing for funded accounts, done right
Position size is not a feeling. It is arithmetic: decide what you will risk, measure the distance to your stop, and let those two numbers dictate size. Here is the exact calculation for the instruments most funded traders use.
The most common way traders blow up is sizing by instinct — "this looks good, I will go bigger." Correct position sizing removes the instinct entirely. You fix the risk first, in dollars; you measure the stop distance; and size becomes a division, not a decision. Do this and your losses stay uniform, your R-multiples stay honest, and no single trade can end you.
Step one: fix your risk per trade
Decide the money you are willing to lose if the trade hits its stop, and keep it constant. A common approach on funded accounts is a small fixed fraction of the drawdown you are allowed — often well under 1% of the account, or a flat dollar figure sized so that a normal string of losers cannot approach the daily limit. The exact number is yours; the point is that it does not change trade to trade based on conviction.
Position size = risk in dollars ÷ (stop distance × value per unit of movement). Everything else is just plugging in the right "value per unit" for your instrument.
Step two: know your value per point
Every instrument moves in its own units, each worth a specific amount. You cannot size correctly without this number. For the futures most prop traders use:
- ES (E-mini S&P 500): $50 per point. MES (Micro): $5 per point.
- NQ (E-mini Nasdaq): $20 per point. MNQ (Micro): $2 per point.
- Forex: a standard lot is roughly $10 per pip on most USD-quoted pairs; a mini lot ~$1, a micro ~$0.10. Cross and JPY pairs differ, so confirm per pair.
Worked example — futures
You are risking $200 per trade on MNQ, where each point is worth $2. Your setup puts the stop 25 points below entry. Size = $200 ÷ (25 points × $2) = $200 ÷ $50 = 4 contracts. If a cleaner setup lets you use a 12-point stop for the same $200 risk, size = $200 ÷ (12 × $2) = $200 ÷ $24 ≈ 8 contracts. Same money at risk, tighter stop, larger size — and critically, an identical −1R if you are wrong. The tighter stop did not make you reckless; the risk stayed fixed.
Worked example — forex
You are risking $150 on a EUR/USD trade with a 30-pip stop. At roughly $10 per pip for a standard lot, one lot would risk 30 × $10 = $300 — too much. Size = $150 ÷ (30 pips × $10) = 0.5 lots. Half a standard lot risks exactly $150 across the 30-pip stop. Use mini or micro lots to hit the number precisely.
Why fixed risk changes everything
- Your losers become uniform. Every stop-out is one clean R, which is what makes expectancy meaningful.
- Stop distance stops being scary. A wider stop simply means a smaller size, not a bigger loss. You can place stops where the structure demands, not where your size forces them.
- No single trade can end you. With risk capped per trade, it takes a long, unlucky string — not one bad click — to hit a limit. That is survivable and, more importantly, reviewable.
When the maths gives 4.7 contracts, trade 4, not 5. Rounding up quietly pushes every trade over your intended risk, and those small overages compound into the breach that ends the account.
Sizing is the least glamorous part of trading and the part that most reliably separates the funded from the failed. Get the arithmetic right once, apply it every single time, and you have removed the decision that does the most damage when left to emotion.
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