Stock Position Size Calculator
How many shares to buy based on your risk per trade.
Enter your values
Enter the account size in $.
Enter the risk per trade in %.
Enter the entry price in $.
Enter the stop-loss price in $.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Shares to buy
- 200
- Position value
- $8,400.00
- Dollar risk if stopped out
- $500.00
- Position as % of account
- 16.8%
Quick answer
Position size is set so the dollar loss from your entry to your stop-loss equals your predetermined maximum risk per trade.
Shares = (account size x risk %) / (entry price - stop price)
At a glance
| What it does | How many shares to buy based on your risk per trade. |
|---|---|
| Category | Investing |
| Inputs needed | Account size, Risk per trade, Entry price, Stop-loss price |
| Main output | Shares to buy |
| Formula | Shares = (account size x risk %) / (entry price - stop price) |
| Cost | Free — no sign-up, no download |
How to use the Stock Position Size Calculator
- 1Enter your total account size and the percentage you're willing to risk per trade (often 1-2%).
- 2Enter your planned entry price and stop-loss price.
- 3The calculator sizes the position so a stop-out only costs your chosen risk percentage.
Inputs explained
- Account size($)
- Enter the account size in $.
- Risk per trade(%)
- Enter the risk per trade in %.
- Entry price($)
- Enter the entry price in $.
- Stop-loss price($)
- Enter the stop-loss price in $.
Worked example
Using the values the calculator loads with:
Inputs
- Account size50000 $
- Risk per trade1 %
- Entry price42 $
- Stop-loss price39.50 $
Results
- Shares to buy200
- Position value$8,400.00
- Dollar risk if stopped out$500.00
- Position as % of account16.8%
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.
What do I need to enter into the Stock Position Size Calculator?
Just 4 values: account size, risk per trade, entry price, stop-loss price. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Stock Position Size Calculator work out the answer?
Position size is set so the dollar loss from your entry to your stop-loss equals your predetermined maximum risk per trade. It applies the formula Shares = (account size x risk %) / (entry price - stop price) and shows the working so you can check each step by hand.
Is the Stock Position Size Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.