Rules verified 10 August 2026
Prop Firm Position Sizing · verified 10 August 2026
Position sizing for prop firm accounts: why account size is the wrong denominator
Verified 10 August 2026 · published account specs from 6 futures prop firms
The problem with percentage-of-account sizing
On your own capital, risking one percent of the account is sound: the account is the thing that can run out. On a prop firm account it is not. What can run out is the distance between your balance and the trailing floor · and that distance does not grow when you profit, because the floor follows you up.
Worked example
| State | Balance | Floor | Room | Risking 2% of balance | % of room |
|---|---|---|---|---|---|
| Day one | $50,000 | $48,000 | $2,000 | $1,000 | 50% |
| Up $3,000 | $53,000 | $51,000 | $2,000 | $1,060 | 53% |
| After two losses | $50,880 | $51,000 | $0 | $1,018 | account breached |
The trader never increased their risk. The denominator moved underneath them.
Sizing from remaining room
Replace the denominator and the arithmetic self-corrects. Risking five percent of remaining room means $100 when you have $2,000 of room and $50 when you have $1,000 · the position shrinks exactly when survival matters most, without a decision being required.
It also makes a single-trade breach mathematically impossible, which is not true of any fixed-dollar or percentage-of-account scheme.
From dollars to contracts
Risk in dollars divided by the cost of your stop for one contract, rounded down. A 20-point stop on NQ at $20 per point is $400 plus commission per contract; on MNQ at $2 per point it is $40. The micro contract is what makes small room tradeable at all · at $2 per point a trader with $80 of room can still take a position, where the standard contract would be impossible.
Frequently asked questions
How should I size positions on a prop firm account?
As a percentage of the distance between your balance and the trailing drawdown floor, not as a percentage of the account size. Because the floor moves up as you profit, account size stops being a meaningful denominator almost immediately. Sizing from remaining room means your risk shrinks automatically as your room shrinks.
What percentage should I risk per trade in a prop firm evaluation?
Lower than you would on your own capital, because the drawdown is smaller relative to the account and the floor moves. A common mechanical starting point is 2 to 5 percent of remaining room per trade, split across the number of attempts you intend to take that day. The exact figure matters less than the denominator being room rather than balance.
How do I calculate my position size in contracts?
Take your risk in dollars, divide by the cost of your stop for one contract, and round down. A 20-point stop on NQ at $20 per point costs $400 plus commission per contract, so $900 of risk buys two contracts, not two and a quarter.
Why does risking a fixed dollar amount fail on a prop account?
Because it is a fixed fraction of a shrinking number. Risking $500 against $2,000 of room is 25 percent. After two losses it is $500 against $1,000, which is 50 percent. The dollar figure never changed but the risk doubled, and then doubled again.