Position Size Calculator
Size a trade so that if the stop-loss is hit you lose only the amount you planned. Enter your account size, the percentage you are willing to risk, your entry and stop prices, and get the number of shares or units to buy or sell short. For education and planning only.
Caps the position value, e.g. 100 for no leverage.
How to use the Position Size Calculator
- Enter your account size and how much you are willing to lose on this trade, as a percentage (1% is a common rule) or a fixed amount.
- Enter the entry price and your stop-loss price. A stop below the entry means a long trade, above it means a short.
- Pick the rounding: whole shares, lots of 100, or decimals for crypto and fractional shares.
- Optionally add a target price to see the reward-to-risk ratio, and a maximum position size as a percentage of the account.
- Read the position size, the money at risk and the position value, and compare other risk levels in the table.
Position sizing formula
Risk amount = account size × risk % (or a fixed amount you choose)
Risk per share = |entry price − stop-loss price|
Position size = risk amount ÷ risk per share, rounded down to a whole share or lot
Example: a $25,000 account risking 1% = $250. Entry $50, stop $47.50, so each share risks $2.50. Position size = 250 ÷ 2.50 = 100 shares, a $5,000 position (20% of the account). If the stop is hit you lose $250; at a $57.50 target you make $750, a 3:1 reward-to-risk.
The stop distance, not the share price, decides how many shares you can hold. A wider stop means a smaller position for the same risk.
Reward-to-risk and the win rate you need
| Reward-to-risk | Break-even win rate | Result of 10 trades at 40% wins (1R = $250) |
|---|---|---|
| 1 : 1 | 50% | 4 × $250 − 6 × $250 = −$500 |
| 1.5 : 1 | 40% | 4 × $375 − 6 × $250 = $0 |
| 2 : 1 | 33.3% | 4 × $500 − 6 × $250 = +$500 |
| 3 : 1 | 25% | 4 × $750 − 6 × $250 = +$1,500 |
Break-even win rate = 1 ÷ (1 + reward-to-risk), before commissions and slippage. This table illustrates the arithmetic only; it says nothing about how likely any trade is to reach its target. This page is for education and planning, not financial advice.
Frequently asked questions
How do you calculate position size?
Position size = amount you are willing to risk ÷ risk per share, where risk per share = |entry price − stop-loss price|. With a $25,000 account, 1% risk ($250), entry $50 and stop $47.50, the risk per share is $2.50, so the position size is 250 ÷ 2.50 = 100 shares.
What is the 1% rule?
The 1% rule is a common risk-management guideline: never risk more than 1% of your trading account on a single trade. It means a string of ten losing trades costs roughly 10% of the account, not half of it. Some traders use 0.5% or 2% instead; the right number depends on your strategy and tolerance.
Does the position size include fees and slippage?
No. The calculation assumes your stop fills exactly at the stop price. Gaps, slippage and commissions can make the actual loss larger, so many traders leave a margin by risking slightly less than their limit.
Why is my position value bigger than my risk amount?
The risk amount is only what you lose if the stop is hit, not the size of the position. A tight stop means a small loss per share, so you can hold many shares; the full position value can be many times the risk amount and may even exceed your account, which would require margin or leverage.
What is reward-to-risk ratio?
Reward-to-risk compares the distance to your target with the distance to your stop. A $50 entry, $47.50 stop and $57.50 target has $7.50 of reward for $2.50 of risk, a ratio of 3:1. At 3:1 you only need to win more than 25% of trades to break even, before costs.
Can I use this for crypto or forex?
Yes for crypto: choose decimal rounding and enter prices in your quote currency. For forex, pip values depend on the pair and lot size, so this share-based calculator works only if you enter prices and size in units of the base currency.
Is this financial advice?
No. The calculator is an informational tool for working out the math of a trade plan. Trading involves risk of loss, and a stop-loss does not guarantee the exit price.