EV = (Win Rate × Avg Win) − (Loss Rate × Avg Loss). Positive EV means the strategy is profitable long-term even with a sub-50% win rate.
Total gross wins divided by total gross losses. Above 1.5 is solid. Above 2.0 is excellent. Below 1.0 means you're losing money overall.
Full Kelly gives the mathematically maximum growth rate but causes extreme drawdowns. Half Kelly (÷2) is the practical standard — most professional traders cap risk at 1–2% regardless.