To call a bet of B into a pot of P you risk B to win P plus B, so you need to win at least B divided by (P + 2B) of the time. A pot-sized bet needs 33.3%; a half-pot bet needs 25%.
That single division decides most poker calls. Everything else is working out your equity accurately enough to compare against it.
The common error is using two-card equity to justify a flop call. A flush draw is 34.97% to complete by the river but only 19.57% on the next card, and the larger figure is correct only if you are all in or certain to see both cards free. Calling on the two-card number and then folding to a turn bet is how players talk themselves into losing calls.
Where the numbers come from
Related terms in poker
- Outs — The cards remaining that would improve your hand to a likely winner.
- Equity — Your share of the pot, meaning how often you win it if the hand plays to showdown.
- Implied odds — The money you expect to win later if your draw comes in, beyond what is in the pot now.
- Position — Where you act in the betting order, and the largest structural edge in poker.
- Button — The dealer position, which acts last on every postflop street.
- Cutoff — The seat immediately to the right of the button.
Where an entry quotes a number, that figure comes from the computed sections of this site rather than from another glossary, so the definition and the derivation cannot drift apart. Each entry links to the page where the number is worked out.