Trading costs: from gross P/L to a usable net estimate
How spread, commission, overnight financing and slippage change gross P/L and strategy break-even.
Separate gross P/L from net P/L
A calculation based only on chart entry and exit prices may be a gross result. Net trading results are affected by spread, commission, overnight swap/financing and, in some cases, currency conversion.
Spread
If one lot has a pip value of 10 and the effective spread cost is 1.2 pips, the simple cash impact is about 12. The smaller the target and stop, the larger this fixed friction becomes relative to the trade's intended payoff.
Commission
Check whether a quote such as “3.5 per lot” is per side or round turn. If it is charged once at entry and once at exit, the full round-trip cost is twice the per-side number.
Swap and holding period
Overnight financing can differ for long and short positions and can include a triple-swap day. On multi-day strategies, accumulated financing can become more important than the entry spread.
Put costs into expectancy
When estimating break-even win rate, use net average wins and losses when possible. The trading cost calculator and break-even win rate calculator help show how friction changes the strategy structure.
Last reviewed: 2026-08-31