Fee-adjusted position size calculator
The size that keeps your all-in loss inside your risk budget once commission, spread, and slippage are counted. The plain calculation always overstates how much you can hold.
Fee-adjusted size
0.40
Risk budget$250.00
Effective stop distance0.006110
All-in cost per unit$618.00
Ignoring costs, size would be0.41
…which would actually lose$253.38
Overrun on your budget$3.38
Run the full check →
Adds your own rules, and what a gap through the stop would cost.
What this covers
Round-turn commission charged per unit, plus spread and slippage expressed in pips.
Assumes cost is symmetric on entry and exit. A venue that charges differently needs its own figure.
Excludes overnight financing, which matters on multi-day holds and is not modelled here.
Formula and assumptions
Effective stop distance = |entry − stop| + (spread + slippage) × pip size.
Cost per unit = effective distance × contract value + commission.
Size = risk budget ÷ cost per unit, truncated down.
Truncated, never rounded up: rounding up puts the all-in loss past the budget.
Assumes the stop fills at the effective price. A gap fills worse still.
fee_adjusted_size.v1
Worked example
Example — not a recommendation.
Account, risk$25,000 at 1% = $250
Entry → stop1.0840 → 1.0900 (60 pips)
Spread + slippage1.1 pips
Commission$7 per lot
Plain size0.41 lots
Fee-adjusted size0.40 lots
Common mistakes
Sizing on the raw stop distance, then losing more than the budget on every single trade.
Counting commission one way when it is charged round turn.
Using a quiet-hours spread for a position held through a news release.
Ignoring slippage entirely because the last few fills happened to be clean.
Limitations
This is arithmetic on numbers you supplied. It does not know your broker, your account, or the market. It does not predict price, does not say whether to take a trade, and is not advice. Maximelion is not affiliated with any broker or prop firm, and nothing here is endorsed by one.
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Last reviewed 25 July 2026