● Toolkit
Position size, from the risk you chose.
Size is not a feeling. Once you have fixed how much of the account one trade may lose and where the stop goes, the size is arithmetic — and so is the fee it drags along.
How this is worked out
- Risk amount = equity × risk%. It is the money you accept losing if the
stop fills, and it is the only input that decides size.
- Stop distance = |entry − stop|, in price. As a percentage it is that
distance divided by the entry.
- Position size = risk amount ÷ stop distance, in units of the asset.
Notional = size × entry. Leverage = notional ÷ equity.
- Round-trip fee = notional × fee% × 2, because you pay to get in
and again to get out.
The last line is the one worth staring at. A stop placed close to the entry buys you a
large position, and a large position pays a large fee — so a tight stop can hand a
surprising share of your intended risk straight to the exchange before the trade has
done anything. The calculator states that share outright.
Two things it deliberately does not model: slippage beyond the fee, and the funding you
pay or receive while the position is open. Both widen the real cost. A figure that
flatters you is worse than no figure.
Costs like these belong in every backtest you are shown, not just this calculator. Our
guide on verifying a trading bot backtest
walks through how to check they are actually in there.