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Calculation Machine

Stock Position Size Calculator

How many shares to buy based on your risk per trade.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Shares to buy
200
Position value
$8,400.00
Dollar risk if stopped out
$500.00
Position as % of account
16.8%

Quick answer

Position size is set so the dollar loss from your entry to your stop-loss equals your predetermined maximum risk per trade.

The formula

Shares = (account size x risk %) / (entry price - stop price)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Account size50000 $
  • Risk per trade1 %
  • Entry price42 $
  • Stop-loss price39.50 $

Result

  • Shares to buy200
  • Position value$8,400.00
  • Dollar risk if stopped out$500.00
  • Position as % of account16.8%

How to use the Stock Position Size Calculator

  1. 1Enter your total account size and the percentage you're willing to risk per trade (often 1-2%).
  2. 2Enter your planned entry price and stop-loss price.
  3. 3The calculator sizes the position so a stop-out only costs your chosen risk percentage.

Frequently asked questions

Why size positions this way?

It keeps any single losing trade from doing significant damage to your account, regardless of the stock's price.

What if the position value exceeds my buying power?

Reduce the risk percentage or widen your stop, since you can't buy more shares than your account allows.

About this calculator