Tools
Position size calculator
Size a perps trade so that a stop-out costs exactly what you chose, after commissions, and check it against the firm’s leverage cap.
How the size is calculated
The calculator solves for the quantity at which the price move to your stop plus entry and exit commission equals your risk budget. It then checks the resulting notional against the leverage cap and reduces the size if needed.
risk = balance × daily limit % × share qty = risk ÷ ( |entry − stop| + fee × (entry + stop) ) notional = qty × entry leverage = notional ÷ balance
Worked example
$10,000 account, 3% daily limit, risking 25% of it = $75. BTC long at $100,000, stop at $99,000, 0.03% commission per fill (MyFundedPerps crypto rate). qty = $75 ÷ ($1,000 + 0.0003 × $199,000) = 0.0708 BTC notional = $7,077.47 · leverage 0.71x · commission $4.23
Frequently asked questions
Why size trades from the daily loss limit?
The daily limit is the rule a single bad day breaks first. Sizing each trade as a fixed share of it caps how many full losses fit in one day before the account fails.
Do commissions change the position size?
Yes. You pay commission on entry and exit, based on the full notional rather than the margin, so it adds to the loss at your stop. The calculator includes both fills.
Does leverage change my risk?
Not directly. Risk is set by size and stop distance. Leverage only caps how big a position the account can open, which matters when the stop is very tight.