Answer first
What this calculator tells you
Calculate how many shares to buy from account size, risk per trade and stop distance. Cap the loss on one trade at a set share of your account before you enter it. Formula: Shares = ⌊(account × risk %) ÷ (entry price − stop price)⌋; position value = shares × entry price. At the worked-example inputs, the shares to buy is 100. Holding every other input steady, moving account size from $20,000 to $30,000 moves the result from 80 to 120.
Transparent method
The formula
Cap the loss on one trade at a set share of your account before you enter it.
Worked example
Example inputs
How to interpret the result
Position sizing works backward from the loss you can accept. With a $25,000 account and a 1 percent risk rule, you can lose $250 on the trade. If the entry is $50 and the stop is $47.50, each share risks $2.50, so the position is 100 shares, worth $5,000. A wider stop means fewer shares for the same dollar risk, which is the point of doing it this way.
At the worked-example inputs the shares to buy is 100. It rises with entry price, risk per trade and account size and falls as stop-loss price increases.
Investment returns are uncertain; taxes, fees, volatility and cash-flow timing can materially change results.
Before you rely on it
What to check
Use a stop price that the chart or the plan justifies, not one picked to make the share count look big. The stop distance drives everything.
The common error
Where people go wrong with position size calculator
Sizing by the dollars you want to invest. That fixes the position and leaves the risk to chance, so a wide stop can cost far more than you meant to lose.
Sensitivity evidence
How account size changes the shares to buy
Holding every other input at the worked-example value, moving account size from $20,000 to $30,000 moves the shares to buy from 80 to 120: a spread of 40, or 40% of the worked-example result.
| Account size | Shares to buy | Position value | Dollars at risk |
|---|---|---|---|
| $20,000 | 80 | $4,000 | $200 |
| $22,500 | 90 | $4,500 | $225 |
| $25,000worked example | 100 | $5,000 | $250 |
| $27,500 | 110 | $5,500 | $275 |
| $30,000 | 120 | $6,000 | $300 |
Every input, tested
Which input moves the shares to buy most
Of the 4 inputs, entry price moves the shares to buy most (33 across the range tested) and account size moves it least (20).
| Input | Tested from | To | Shares to buy at each end | Swing |
|---|---|---|---|---|
| Entry price | $45 | $55 | 0 to 33 | 33 (33%) |
| Stop-loss price | $43 | $52 | 35 to 0 | 35 (35%) |
| Risk per trade | 0.750% | 1.3% | 75 to 125 | 50 (50%) |
| Account size | $22,500 | $27,500 | 90 to 110 | 20 (20%) |
Two variables at once
Shares to buy by account size and risk per trade
Across the grid the shares to buy runs from 40 to 180. Moving account size from $20,000 to $30,000 shifts it by 40 at the middle column, and moving risk per trade from 0.500% to 1.5% shifts it by 100 at the middle row, so risk per trade is the bigger lever here.
| Account size \ Risk per trade | 0.500% | 1.0% | 1.5% |
|---|---|---|---|
| $20,000 | 40 | 80 | 120 |
| $22,500 | 45 | 90 | 135 |
| $25,000 | 50 | 100 | 150 |
| $27,500 | 55 | 110 | 165 |
| $30,000 | 60 | 120 | 180 |
The highlighted cell is the worked example: 100.
Step by step
The worked example, input by input
| Input | Value used | What it means |
|---|---|---|
| Account size | $25,000 | Enter the account size used in this calculation. |
| Risk per trade | 1.0% | The share of the account you accept losing if the stop is hit. |
| Entry price | $50 | Enter the entry price used in this calculation. |
| Stop-loss price | $48 | Below the entry for a long position. |
| Shares to buy | 100 | |
| Position value | $5,000 | |
| Dollars at risk | $250 | |
Inputs, definitions and assumptions
Account size
Enter the account size used in this calculation. The prefilled worked-example value is $25,000.
Risk per trade
The share of the account you accept losing if the stop is hit. The prefilled worked-example value is 1.0%.
Entry price
Enter the entry price used in this calculation. The prefilled worked-example value is $50.
Stop-loss price
Below the entry for a long position. The prefilled worked-example value is $48.
How to use this calculator
- 1Verify the inputs. Gather account size, risk per trade, entry price and stop-loss price from your own documents; the prefilled values are examples.
- 2Save a baseline. The worked example puts the shares to buy at 100. Store your own version of it as Scenario A.
- 3Test one change. Start with entry price, the input with the biggest effect here: moving entry price from $45 to $55 takes the shares to buy from 0 to 33, a swing of 33% of the worked-example figure.
- 4Check the extremes. At half the example entry price ($25) the shares to buy is 0; at double ($100) it is 4.
People also ask
Frequently asked questions
How do you calculate position size?
Shares = ⌊(account × risk %) ÷ (entry price − stop price)⌋; position value = shares × entry price. Enter account size in dollars, risk per trade in percent, entry price in dollars and stop-loss price in dollars (1 means 1%). At the worked-example inputs the shares to buy is 100.
What does the position size result mean?
Cap the loss on one trade at a set share of your account before you enter it. At the worked-example inputs the shares to buy is 100. It rises with entry price, risk per trade and account size and falls as stop-loss price increases.
How much does account size change the shares to buy?
Holding every other input at the worked-example value, moving account size from $20,000 to $30,000 moves the shares to buy from 80 to 120, a spread of 40.
What are the limits of this position size calculator?
Investment returns are uncertain; taxes, fees, volatility and cash-flow timing can materially change results. The tables on this page test account size only from $20,000 to $30,000; a value outside that range is not tabulated here.
Which input moves the shares to buy most in the position size calculator?
Ranked by how far each moves the shares to buy across the range tested: entry price (33, 33%), stop-loss price (35, 35%), risk per trade (50, 50%) and account size (20, 20%).
If I double entry price in the position size calculator, does the shares to buy double?
Doubling it from $50 to $100 takes the shares to buy from 100 to 4, which is 0.04 times the worked-example figure. So it falls instead of rising. Halving it to $25 gives 0.
How much does risk per trade matter in the position size calculator?
The worked example uses 1.0%. Holding every other input at its worked-example value, moving risk per trade from 0.750% to 1.3% takes the shares to buy from 75 to 125, a swing of 50% of the worked-example figure.
How much does entry price matter in the position size calculator?
The worked example uses $50. Holding every other input at its worked-example value, moving entry price from $45 to $55 takes the shares to buy from 0 to 33, a swing of 33% of the worked-example figure.
How much does stop-loss price matter in the position size calculator?
The worked example uses $48. Holding every other input at its worked-example value, moving stop-loss price from $43 to $52 takes the shares to buy from 35 to 0, a swing of 35% of the worked-example figure.
Which inputs change the position value in the position size calculator?
At the worked-example inputs it is $5,000. Account size takes it from $4,500 to $5,500, risk per trade takes it from $3,750 to $6,250, entry price takes it from $0.00 to $1,815 and stop-loss price takes it from $1,750 to $0.00.
Which inputs change the dollars at risk in the position size calculator?
At the worked-example inputs it is $250. Account size takes it from $225 to $275, risk per trade takes it from $188 to $313, entry price takes it from $0.00 to $248 and stop-loss price takes it from $245 to $0.00.
Sources and evidence
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