Position Size Calculator
Stop guessing how much to risk.
A free position size calculator that tells you exactly how many shares to buy given your account, risk per trade, and stop-loss. Updates live — no signup, nothing saved.
0.25%5%
Your position size
Fill in your entry and stop-loss above — the exact position size appears here instantly.
The math of survival
Why position sizing matters more than entry timing
Most traders obsess over entries — the perfect setup, the perfect moment. But entries decide whether a trade wins. Position sizing decides whether you survive long enough for winning to matter. A mediocre entry with correct sizing costs you a small, planned amount. A brilliant entry with reckless sizing can end an account.
The reason is asymmetry. Lose 10% of your account and you need an 11% gain to recover. Lose 50% and you need 100%. Consistent risk-per-trade — say, 1% — turns every losing streak into arithmetic instead of catastrophe: twenty consecutive losses at 1% still leaves you with more than 80% of your capital and, more importantly, the composure to keep executing your process.
Fixed-fractional sizing also removes a decision you should never make in the moment: "how much do I feel like putting on this one?" That question is where overconfidence bias does its damage — sizing a position based on how confident a trade feels rather than a fixed rule is one of the most common ways it shows up. And once a sized position moves against you, loss aversion makes cutting it feel far worse than the math says it is. A pre-committed size and stop take both biases partly out of play.
Step by step
How to use this calculator
Enter your account size
The total capital you're trading with — not the amount you'd like to have, the number that's actually in the account.
Set your risk per trade
The percentage of the account you're willing to lose if the stop gets hit. 1% is the standard starting point; move it only with evidence.
Enter your entry and stop-loss prices
The stop must be decided before the trade, from the chart — not moved afterwards to fit a size you wanted. The distance between entry and stop is what drives the math.
Take the position size it gives you
That's the maximum size that keeps your loss at your chosen risk. If the number feels small, that's the point — small is what survives.
Questions
Position sizing, answered
What is position sizing?
Position sizing is deciding how many shares, units, or contracts to buy or sell so that a single trade can only lose a fixed, pre-chosen amount of your account. Instead of asking 'how much can I make?', it starts with 'how much am I willing to lose?' and works backwards from your stop-loss to a position size that keeps that loss constant.
How much should I risk per trade?
Most disciplined traders risk between 0.5% and 2% of their account on any single trade. At 1% risk, you could be wrong twenty times in a row and still have most of your capital intact. Risking 5–10% per trade, by contrast, means a normal losing streak can permanently damage the account.
What's a good risk percentage for beginners?
Start at 0.5% or 1% and treat it as a hard ceiling, not a target. The goal early on is surviving long enough to build a track record. You can revisit the number after a hundred logged trades — most beginners who size up early are doing it out of confidence, not evidence.
Does this work for options or futures?
The core formula — risk amount divided by stop distance — works anywhere you can define a stop-loss price. For futures, divide the dollar risk by the stop distance measured in dollars per contract (points × tick value). For options, position sizing is fuzzier because of the Greeks, but risking a fixed fraction of the account per idea still applies.
Want to check your reasoning too, not just your position size?
The right size with the wrong reasoning still loses. Run your thinking through the Bias Checker before you enter.
Check My ReasoningTrack whether your sizing discipline actually holds.
The Decision Journal logs your reasoning, confidence, and outcomes — so you can see whether your rules survive contact with real trades.
Start your free Decision Journal