Stock Position Size Calculator
Calculate how many shares fit your risk per trade using account size, entry price and stop-loss price. Review the planned dollar risk, position value and the constraint that limits the result.
Define the loss before the size
Advanced settings
Worked example
Work from risk per trade to the number of shares
For a $10,000 account and a 1% risk budget, planned risk is $100. A $50 entry and a $48 stop create $2 risk per share. Before fees and slippage, $100 ÷ $2 allows 50 shares, costing $2,500. If you cap capital allocation at 20% of the account, the $2,000 cap limits the position to 40 shares instead.
Continue with the related guides
Frequently asked questions
What is the stock position size formula?
Shares equal the risk budget divided by risk per share, rounded down when whole shares are required. A capital allocation limit can reduce that share count further.
What happens when the stop is wider?
With the same dollar risk budget, a wider stop means fewer shares. Doubling risk per share halves the risk-based share count before fees and allocation limits.
Does a 1% risk budget guarantee I lose no more than 1%?
No. It describes planned risk at the assumed execution price. Gaps, slippage and limited liquidity can produce a larger realized loss.
How to use
From inputs to a result you can review
- Choose long or short and enter the account size.
- Set risk as a percentage or fixed dollar amount.
- Enter the planned entry and stop-loss price.
- Add allocation limits, fees, slippage, or fractional shares when needed.
- Review the share count, position value, planned loss and binding constraint.
Known limitations
What this calculation does not know
- A stop price is not a guaranteed execution price.
- Gap, liquidity, borrow, tax, and leverage risks are not fully modeled.
- The result does not determine whether the trade is suitable.
- Whole and fractional shares are rounded down to avoid exceeding the risk limit.
Educational calculation only. This is not personalized investment, trading, or tax advice.
Read the guide
Position size vs stop-loss: which comes first?
Learn why the invalidation level usually comes first and how it controls share count.
Read the guide →Method version 1.0
Calculation logic reviewed against the published methodology and automated test cases. Last updated August 5, 2026.