Position Size Calculator
Enter your account size, risk per trade, entry, and stop. We'll tell you exactly how many shares to buy.
Doing this before every trade? Fuselit automates position sizing, trailing stops, and rebuys on your Alpaca account.
Try Fuselit free →How to use this calculator
The math is simple: decide what dollar amount you're willing to lose if your stop hits, then divide by the per-share risk. The calculator rounds down to whole shares so you never accidentally exceed your risk budget.
Why position sizing matters
A trader with a 55% win rate and 1:1 risk/reward will still hit a 6-loss streak roughly once a year. If each loss is 1% of equity, the drawdown is around 6%. If each loss is 5%, the drawdown is 26% — and you need a 35% gain to recover. Position sizing is the single biggest determinant of whether a strategy survives long enough to express its edge.
Frequently asked questions
How do you calculate position size for a stock trade?
Multiply your account size by the percentage you're willing to risk on the trade. Divide that dollar risk by the per-share risk (the absolute difference between your entry price and your stop-loss). The result, rounded down, is the number of shares to buy.
What is a good risk percentage per trade?
Most professional traders risk 0.5% to 2% of account equity per trade. 1% is a common default — it lets you survive a long losing streak without catastrophic drawdown. Beginners often start at 0.5%.
Why does position sizing matter more than picking winners?
Even a 60% win rate strategy will hit losing streaks of 5–10 trades. If each loss is 10% of your account, you go bust. If each loss is 1%, you barely notice. Position sizing is what turns an edge into a survivable system.
Should position size include the cost of the position or just the risk?
Both matter. This calculator sizes by risk (entry minus stop), then shows you the total notional so you can confirm it fits your account. If the notional exceeds your available cash, your stop is too wide for your risk tolerance.