The 80/20 Rule for River Value Bets

The working rule for river value: if your hand is good about 80% of the time against your opponent's full arriving range, it is strong enough to bet pot. The cleanest way to apply it is inverted. Count how often you are beat, starting from the best hand class and working down, and check the total against 20%.

The pure theory is looser than that. Against a pot-sized bet your opponent defends about half their range, so on paper you profit whenever you beat more than half of the calling half, which means being beat anything under 25% would do. Practice tightens it to roughly 20% for two reasons. Blockers let good opponents call and raise with better selection than the raw math assumes. And you can get raised, sometimes by hands worse than yours that fold out your better one. The gap between 25 and 20 is the price of those two facts.

Clearing the bar to pot does not mean pot is best. As you approach the 20% line, smaller bets overtake the big one, because the largest sizing keeps running into the top of the range while a smaller bet drags in calls from hands a pot bet folds out. Roughly: pot is clearly best somewhere around 15% beat and better, half pot carries you into the mid-to-high 20s, and third pot stays profitable up into the low 30s before checking takes over. One important exception. If the line you took only ever bets pot, bet pot anyway. A rare small bet in a pot-only line is read with near-clairvoyance and check-raised, and balancing that small size properly costs your normal hands more than the thin bet earns.

The whole calculation runs on knowing how often each class shows up in a range that has called down, which is a memorizable skill rather than a talent. The hand distribution page gives exact class frequencies per board, and the bet sizing reference covers which sizes the solves actually use street by street. Two streets of value is its own question with its own threshold, and that one is covered in the two-street rule.