Position Size Calculator
How many shares or units to buy so that, if the stop-loss is hit, you lose no more than a chosen percentage of the account.
Results
Units to buy (whole)
40
Amount you are willing to lose
100.00
Risk per unit
2.5000
Position value
2000.00
Position as a share of the account
20.00
%
What this tool does
The question is not how much to invest but how much you are prepared to lose: risk a fixed share of the account — 1 % is a common rule of thumb — and let the distance to the stop decide the size. A tight stop allows a bigger position, a wide stop a smaller one, for the same loss. The result is rounded down to whole units, and it ignores gaps, slippage and fees, which can make the real loss larger than planned.
Formula
units = (balance × risk % ÷ 100) ÷ |entry − stop|
Variables
| Symbol | Meaning | Unit |
|---|---|---|
ba | Account balance | — |
rp | Risk per trade | % |
ep | Entry price | — |
sp | Stop-loss price | — |
UN | Units to buy (whole) | — |
RA | Amount you are willing to lose | — |
PU | Risk per unit | — |
PV | Position value | — |
PS | Position as a share of the account | % |
Worked example
- Account balance10,000
- Risk per trade1 %
- Entry price50
- Stop-loss price47.5
- Units to buy (whole)40
- Amount you are willing to lose100.00
- Risk per unit2.5000
- Position value2000.00
- Position as a share of the account20.00 %
Limitations
- This is an informational calculator, not personalised financial advice. Rates, fees, taxes and contract conditions vary between institutions and countries.
- The tool works with whatever currency you use for the inputs; it does not convert between currencies.