Pot odds are the price of a call. If the pot is laying you better odds than your chance of winning, calling makes money over time — even when you miss most of the time.
To call X into a pot of P you need to win at least X ÷ (P + X) of the time. That fraction is your break-even equity.
Pot is $80. Villain bets $20. You must call $20 into $100 (the pot after their bet). Break-even = 20 ÷ 120 ≈ 16.7%. A nine-out flush draw on the turn is about 18% — a call. The same draw facing a pot-sized $80 bet needs 80 ÷ 240 ≈ 33% — a fold unless implied odds save it.
Pot odds only count money already in the middle. Implied odds add what you expect to win on later streets if you hit. Deep stacks and a calling station behind you make speculative hands cheaper. A nit who never pays off makes them more expensive (reverse implied odds).
On the flop, outs × 4 ≈ chance to hit by the river. On the turn, outs × 2 ≈ chance to hit the river. Compare that percent to the break-even number above. Full table: outs and drawing odds.
Divide the amount you must call by the pot after you call. Call 20 into 100 → 20 ÷ 120 ≈ 16.7% equity needed.
On the flop, multiply outs by 4 for a river estimate. On the turn, multiply by 2 for the next card.