Position Size Calculator with Commission & Spread
A $100 stop actually costs you $100 plus commissions, spread and slippage. This calculator gives the position size implied by the inputs you choose, fees included, rounded down.
How the calculator works
A classic position size calculator divides your risk budget by the distance to your stop. This one also counts what you pay to get in and out: commission on both orders (with minimums), spread and expected slippage at the stop. It then shows the largest size that keeps the total loss at the stop within your budget, rounded down so rounding never pushes you over it.
Worked example (hypothetical): $25,000 account
Risk 0.75% = $187.50. Entry $52.40, stop $51.80, commission $0.005 per share per order ($1 minimum), slippage allowance $0.02 per share at the stop.
| Simple division | Fees included | |
|---|---|---|
| Calculation | 187.50 / 0.60 | loss per share 0.60 + 0.02 + 0.01 commission |
| Position size | 312 shares | 297 shares |
| Loss at the stop, after fees | $196.56 (0.79%) | $187.11 (0.75%) |
The simple division looks right but breaks the risk rule by about 5% once costs are counted. With a tight stop or a high commission, the gap gets much larger.
Forex, futures and crypto
- Forex: size is shown in units and lots (standard 100,000, mini 10,000, micro 1,000). If the quote currency differs from your account currency (USDJPY with a USD account), enter the conversion rate.
- Futures: enter the tick size and tick value of your contract (e.g. 0.25 and $12.50); commissions are per contract, round turn.
- Crypto: maker/taker fees as a % per order; use a size step matching your exchange (e.g. 0.001).
All formulas and limits are on the methodology page.
Apply this calculation to your whole history
This calculation covers one trade. TrueLedger applies it to every trade in Excel or Google Sheets and shows which markets, hours, setups and behaviours really cost you money.
View the journal on Etsy →