Futures position size calculator
Enter your account size, how much of it you are willing to lose on one trade, and where your stop is. You get the number of contracts that keeps the loss within that limit.
Runs in your browser. Nothing you type is uploaded. · Data checked 2026-10-15
How it works
The formula
Contracts = account × risk % ÷ (stop distance in points × point value + round-trip costs), always rounded down.
Example: $50,000 × 1% = $500 you are willing to lose. An ES stop 4 points away costs 4 × $50 + $5 commission = $205 per contract, so you can trade 2 contracts and risk $410.
Why size from the stop
The same 1% risk means a different number of contracts for a stop of 4 points and a stop of 20 points. Sizing from the stop keeps every trade's loss about the same, so one bad trade does not undo ten good ones.
Gaps and slippage
A stop order can fill worse than its price, especially across a weekend or a news release. The risk figure is a plan, not a guarantee; leave room for it.
Questions
What percentage of my account should I risk per trade?
Many traders keep it between 0.5% and 2%. A smaller percentage leaves room for a losing streak: ten losses in a row at 2% each take about 18% of the account.
Why does the calculator say 0 contracts?
One contract would lose more than your risk budget at that stop. A micro contract, a closer stop or a higher risk percentage brings it within the limit.
Should I include commissions?
Yes. For small stops the round-trip commission and fees are a noticeable part of the loss, so the calculator adds them to the risk of each contract.
Does it work for TAIEX futures?
Yes. Pick TX, MTX or TMF; the amounts are then in New Taiwan dollars.
Test the idea on years of data, not one trade
AlphaPrime generates and backtests futures strategies on your GPU, with contract specs, trading costs and sessions built in, then exports the strategy code for your trading platform.
For education. Not investment advice. Check the exchange before you trade.