Position Size Calculator — Trade Sizing by Risk %
Calculate the exact number of shares, units or lots to buy based on your account size, risk per trade and stop-loss distance.
Pros risk 0.5–2% per trade. Above 5% is gambling.
Your position size, decoded
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Why position sizing is the #1 skill
The biggest gap between profitable traders and amateurs is not which charts they read — it's how much they risk per trade. Pros risk 0.5–2% of their account on any single position. Amateurs risk 20–50% and wonder why they blow up.
How this calculator works
You give it: your total account size, the percentage you're willing to lose on this trade, your entry price, and your stop-loss price. It tells you exactly how many shares to buy so that hitting your stop loses precisely that percentage — no more.
The math
Position size = (account × risk %) ÷ (entry − stop). If your $10,000 account risks 1% on a trade with $2 of risk per share, you buy 50 shares. Stop hits → you lose $100 (1%). Target hits → you keep the rest of the move.
Sizing decides the loss on one trade. Whether a series of them is worth taking at all is a different question, and the Kelly criterion calculator is the arithmetic usually reached for there — with the caveat that it needs an edge you can actually estimate.
How to use the Position Size Calculator
Takes about a minute. No signup, no download, your data stays in your browser.
- 1Open the tool. Scroll up to the Position Size Calculator above — it loads instantly in your browser, no install needed.
- 2Enter your values. The fields come pre-filled with realistic defaults so you can see how it works — replace them with your own numbers.
- 3Read the result. The output updates instantly. Copy or share it — nothing is uploaded to a server, everything stays on your device.
Frequently asked questions
Common questions about the Position Size Calculator.
What determines the position size?
How much you are willing to lose on the trade, and how far the stop sits from the entry. Those two fix the size — the amount at risk divided by the risk per unit. Choosing a size first and discovering the risk afterwards is the same calculation run backwards, and it is how people end up with exposure they did not intend.
Why does a tighter stop allow a larger position?
Because the same total risk is spread over a smaller price move, so more units fit inside it. The trap is that a tighter stop is also more likely to be hit by ordinary noise, so the larger position comes with a higher chance of taking the loss. The two effects pull against each other.
Does correct sizing make a trade safe?
No. It makes the loss on any single trade a figure you chose rather than one you find out afterwards, which is worth having and is not the same as safety. Trading carries substantial risk including losses beyond the amount deposited on leveraged positions.
What is not included?
Commissions, the spread, slippage when a stop is filled worse than its level, and any overnight financing. A gap through your stop can also produce a loss larger than the calculation, which is the main reason a sized position is a plan rather than a guarantee.
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