Position Size Calculator
Given account size + risk tolerance + entry + stop, compute the exact position you should take. Plus R:R ratio, expected value, and Kelly sizing.
Trade setup
Sizing
low leveragePosition size (USD notional)
$3.7K
0.050000 units · 0.4x leverage on $10,000 account
Risk amount
$100
worst case, at stop
Stop distance
2.67%
$2.0K per unit
Take-profit target
2.50R
reward / risk ratio
Target PnL
+$250
if target hit
Favorable R:R. Even at 40% hit rate, setup is +EV long-term.
Kelly sizing (optional)
For when you know your system's historical win rate + average win/loss. Kelly gives the mathematically-optimal bet size.
Full Kelly
32.50%
of bankroll per trade (full Kelly)
Half Kelly
16.25%
safer, most quants use this
Expected value
+0.650R
per trade
Kelly over 25% usually means overfit stats. Backtest on more data before sizing this aggressively. Half Kelly is the conservative floor.
Formula: Position notional = (account × risk%) / stop-distance%. So a $10k account risking 1% with a 2% stop puts $5k notional on the table. Kelly: f = p − (1 − p)/b, where p is win rate and b is win/loss ratio. Most practitioners use half Kelly because real-world distributions have fatter losing tails than assumed. Fees + funding not included.