Position Size Calculator

The single most important number in trading isn't the entry — it's how much you put on. Enter your account, the risk you'll accept, your entry and your stop, and get the exact size that keeps one trade from hurting you. Research and education only — not financial advice.

Instrument

Account size ($)

Risk per trade (%)

Entry price ($)

Stop price ($)

Position size

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Dollar risk

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Position value

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Risk per unit

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Size is rounded down so you never exceed your risk. For options, one contract controls 100 shares, so the calculator assumes your stop is a premium level — see why resting stops on cheap options misfire before using a hard intraday stop on a sub-$1 premium.

Sizing is the edge most rooms never talk about. In our own published backtest, the difference between survivable and account-ending wasn't the picks — it was the sizing. We put every model card's levels on a public record before the move so the risk is visible, not implied. Join the floor →

How risk-based sizing works

Pick a fixed slice of your account you're willing to lose on any one trade — most disciplined traders use 0.5% to 2%. That's your dollar risk. Divide it by your risk per unit (entry minus stop, per share) and you get the size. Because the size adjusts to how far away your stop is, a tight-stop trade lets you hold more shares and a wide-stop trade fewer — but the dollar you can lose stays constant. That constancy is what keeps a losing streak survivable. See position sizing and the risk/reward ratio for the full logic.

Common questions

What risk % should I use?

There's no correct answer, but smaller is safer: at 1% per trade, ten losers in a row costs about 10% of the account; at 5% per trade, that same streak costs roughly 40% and needs a 67% gain just to recover. Over-sizing is the most common way accounts die.

Why round down instead of up?

Rounding down guarantees the trade risks no more than your chosen amount. Rounding up would quietly push you over your own limit — the opposite of the point.

Does this work for options?

Yes, if you define your stop as a premium level (e.g. exit if the option falls from $1.00 to $0.50). The per-contract risk is that premium drop × 100. Remember that options can gap and a resting stop may not fill at your level.

Disclosures. This calculator is a research and education tool. Its outputs are illustrative estimates, exclude commissions, slippage, and gap risk (a stop may not fill at your price), and are not a recommendation to buy or sell any security or derivative. Trading involves substantial risk of loss. ClaudeQuantAlgo is not a registered investment adviser or broker-dealer. You are solely responsible for your own trading decisions. Never risk money you cannot afford to lose.