Expectancy math: why win rate alone means nothing

Most beginners obsess over win rate, thinking a 70% win rate guarantees success. It doesn't. If you don't account for the size of your wins versus your losses, you are flying blind. Expectancy is the only metric that tells you if a strategy has a mathematical edge. The formula is simple: (Win Rate Average Win) - (Loss Rate Average Loss).

Consider two hypothetical systems. System A has a 40% win rate. When it wins, it gains $300, but when it loses, it only loses $100. The math is (0.40 300) - (0.60 100), which equals an expectancy of +$60 per trade. Even with a sub-50% win rate, this is a profitable system.

Now look at System B. It hits a 70% win rate, which feels great. However, its average win is only $50, while its average loss is $200. The math here is (0.70 50) - (0.30 200), resulting in an expectancy of -$25 per trade. Despite winning the majority of the time, this system bleeds capital.

This is why risk-to-reward ratios are just as critical as your hit rate. You can survive with a very low win rate if your winners are large enough, but you will eventually go broke if your losses consistently outweigh your gains, no matter how often you are right. Are you tracking your average win-to-loss ratio alongside your win percentage?