Position Size Calculator
Find the exact number of shares to buy so a losing trade costs you no more than you intend to risk. Enter your account size, risk per trade, entry price, and stop-loss — the math updates instantly.
Trade details
Total trading capital
Percent of account to risk
Price you plan to buy at
Price you will exit at a loss
Position size
- Total dollar risk
- $250.00Target: $250.00
- Risk per share
- $2.00
- Position value
- $6,250.00
- Position as % of account
- 25.00%
Shares are rounded down so your actual risk never exceeds the dollar amount you set. This tool does not account for commissions, slippage, or margin.
How position sizing works
Position sizing is the single biggest lever in risk management. Instead of guessing how many shares to buy, you let your maximum acceptable loss decide the size for you. The formula is simple:
- Dollar risk = account size × (risk % ÷ 100)
- Risk per share = | entry price − stop-loss price |
- Shares to buy = floor(dollar risk ÷ risk per share)
For example, on a $25,000 account risking 1% per trade, your dollar risk is $250. Buying at $50 with a stop at $48 puts $2 of risk on each share, so you can buy 125 shares — a $6,250 position, or 25% of the account, while still only risking $250 if the stop is hit.
Keeping risk constant across trades means no single loss can badly damage your account, and it lets you compare very different setups on equal footing.
Frequently asked questions
How do you calculate position size?+
First find your dollar risk: account size multiplied by your risk percentage (e.g. $25,000 × 1% = $250). Then find your risk per share: the absolute difference between entry and stop-loss price. Divide dollar risk by risk per share and round down to get the number of shares to buy.
What is a good risk per trade percentage?+
Most risk-management frameworks suggest risking 1% to 2% of your account on any single trade. Risking 1% means a string of losing trades has a far smaller impact on your capital than risking 5% or 10% per trade.
Why round the number of shares down?+
Rounding down guarantees your actual dollar risk stays at or below the amount you intended to risk. Rounding up would push your risk slightly above your limit.
Does this calculator account for commissions or slippage?+
No. It gives you the theoretical position size from your entry, stop, and risk inputs. Real fills, commissions, and slippage can shift your true risk slightly, so treat the output as a close starting point.