Why Win Rate Alone Says Almost Nothing About a Scalping Edge
Posted: Mon Oct 26, 2026 1:28 pm
A high win rate feels reassuring, yet it describes only how often trades close in profit, not how much is made or lost per trade. Expectancy combines both: average win multiplied by win probability, minus average loss multiplied by loss probability.
Consider a scalper winning 80 percent of trades with an average win of 3 pips and an average loss of 15 pips. Expectancy per trade is 0.8 times 3 minus 0.2 times 15, which equals negative 0.6 pips before costs. Another scalper winning only 40 percent with 10-pip wins and 5-pip losses earns 0.4 times 10 minus 0.6 times 5, or positive 1 pip. The lower win rate produced the better system.
Costs belong inside the calculation. Spread and commission reduce every win and enlarge every loss, which matters enormously when average wins are only a few pips. Expressing expectancy in R multiples, where one R equals the initial risk, makes results comparable across different stop sizes and position sizes.
Tracking expectancy over a meaningful batch of trades, not a single session, shows whether an edge actually exists or whether a pleasant win rate is masking a slow leak.
Consider a scalper winning 80 percent of trades with an average win of 3 pips and an average loss of 15 pips. Expectancy per trade is 0.8 times 3 minus 0.2 times 15, which equals negative 0.6 pips before costs. Another scalper winning only 40 percent with 10-pip wins and 5-pip losses earns 0.4 times 10 minus 0.6 times 5, or positive 1 pip. The lower win rate produced the better system.
Costs belong inside the calculation. Spread and commission reduce every win and enlarge every loss, which matters enormously when average wins are only a few pips. Expressing expectancy in R multiples, where one R equals the initial risk, makes results comparable across different stop sizes and position sizes.
Tracking expectancy over a meaningful batch of trades, not a single session, shows whether an edge actually exists or whether a pleasant win rate is masking a slow leak.