Free tool · no sign-up

Position size calculator

Size is decided by the stop, not by how much you like the setup. Give this your account, the percentage you will risk, and the distance to your stop, and it returns the share count that keeps the loss where you said it would be.

Stop must be below entry for a long, above for a short. Nothing you type is sent anywhere; the maths runs in your browser.

How it works

Shares equal the dollars you are willing to lose divided by the distance from entry to stop. Risk 1% of a $25,000 account with a $1.50 stop and the answer is 166 shares, whatever the stock is.

Position value is a separate constraint. A tight stop can produce a share count worth more than the account, which is a margin question rather than a risk question, so the percentage of account is shown alongside.

Share counts round down. Rounding up puts more at stake than the rule you just set, which defeats the point of having one.

Common questions

What risk percentage should I use?

The arithmetic does not care, and nobody can tell you a correct number. What matters is that it is fixed in advance and the same on every trade, because a rule you move after a loss is not a rule.

Why does a tighter stop give a bigger position?

Because risk is the distance to the stop multiplied by the shares. Halve the distance and you can hold twice the shares for the same dollar loss. That also doubles what a gap through the stop costs you, which is the part the formula cannot price.

Does this work for options?

Not directly. A defined-risk options position already has a maximum loss, which is the debit paid or the width less the credit, so size it by contracts against that figure instead of a stop distance.

SES Technology Ventures LLC. These tools are for arithmetic, not advice.