Equity
Your percentage chance of winning the hand at showdown
Definition
Equity is the percentage of times a hand wins against an opponent's range if all remaining cards were dealt out right now, over a large number of simulations. It's computed with an equity calculator (Monte Carlo algorithm or full enumeration). Equity is dynamic: it evolves with each new community card based on the possible combinations. Knowing your approximate equity is fundamental to making good calling and raising decisions — particularly to compare your equity to the pot odds and determine whether a call is profitable. Equity is calculated not hand vs hand (one specific hand against another) but above all hand vs range (one hand against the full set of hands your opponent can have in this spot). That distinction is crucial: your real equity depends on the range you assign your opponent, not on a hypothetical single hand.
AA vs KK preflop: AA has ~82% equity. 87s vs AKo preflop: 87s has about 41% equity despite facing two overcards. KQs (top pair) on a K72r board has equity that depends heavily on the opponent's range: high (~80%) against a wide range of draws and weaker pairs, but much lower against a range concentrated in sets and two pairs.