Fees and slippage are quoted as a % of price. Your edge is measured in R, the size of a full loss. This converts one into the other, so the two can be compared.
Costs take the whole edge: +0.13R before costs becomes -0.01R per trade.
With the dollar risk per trade fixed, cost in R is the round-trip cost divided by the stop distance. 0.2% of fees and slippage is 0.07R on a 3% stop and 0.13R on a 1.5% stop. Tighten the stop and every trade pays more of R, and tighter stops usually mean more stop-outs to pay it on.
Before costs, break-even win rate = 1 ÷ (1 + payoff). With a cost of c R per trade it becomes (1 + c) ÷ (1 + payoff). At a payoff of 2 and a cost of 0.2R that moves break-even from 33.3% to 40%.
The last line of the calculator is check 3 on the checklist: the round-trip cost at which the edge disappears. If your real costs sit close to it, small changes in slippage decide whether the strategy works. For a book that rebalances every day, use the turnover-cost calculator instead.
The one-page checklist, free. Confirm the email and the PDF opens straight away; one worked check each Tuesday after that.
Arithmetic only; nothing here is a result of any strategy or investment advice.