Rule of 2 and 4: Estimate Your Odds Fast, and Know Its Limits
The rule of 2 and 4 turns your outs into a percentage without a calculator: multiply them by 4 when you will see two more cards, by 2 when you will see only one. A flush draw has 9 outs, so about 36% from the flop to the river and 18% for a single card. The rule stays within 1 point of the exact odds up to 8 outs; above that, ×4 overestimates more and more.
Try it on a flop draw
The button bets a quarter of the pot, 25%, on K♥ 7♣ 2♣; you hold 9♣8♣ in the big blind. Use the rule: ×4 or ×2, and is the call worth it? Fold, call or raise?
See the answer
Which multiplier. You have 9 outs. The button can bet again on the turn, so the price you pay now buys one card, not two: 9 × 2 = 18%. The exact chance for the turn card alone is 9 ÷ 47 = 19.1%.
The price. On a pot of 100, the call costs 25 for a pot that will hold 150 in total (125 before your call): a threshold of 16.7%.
The decision. 18% already beats 16.7%, so calling is the expected answer. Using ×4 (36%) here would credit you with a river card that this price does not guarantee.
How close is the rule to the exact odds?
| Outs | ×4 | Two cards | ×2 | One card |
|---|---|---|---|---|
| 4 | 16% | 16.5% | 8% | 8.5% |
| 8 | 32% | 31.5% | 16% | 17% |
| 9 | 36% | 35% | 18% | 19.1% |
| 12 | 48% | 45% | 24% | 25.5% |
| 15 | 60% | 54.1% | 30% | 31.9% |
"Two cards" is the exact chance from the flop to the river; "one card" is the exact chance on the turn, out of 47 unseen cards. Two patterns stand out:
- ×4 overestimates big draws. Above 8 outs, the gap passes 1 point; subtract the outs above 8: with 12 outs, 48 − 4 = 44 against 45% exactly; with 15 outs, 60 − 7 = 53 against 54.1%.
- ×2 slightly underestimates. Each unseen card is 1 in 46 or 47, a little more than 2%: add a point when the decision is close.
×4 or ×2: the question that matters
×4 assumes you will see both the turn and the river for the price you are paying now. That is true when you are all‑in on the flop, or when your opponent will not bet again. Facing a flop bet with a turn bet still possible, you are paying for one card: use ×2, as in the spot above.
From the percentage to the decision
The rule only estimates your chance to hit. To decide, compare it with the price of the call, the pot odds; and to count the outs it starts from without mistakes, see poker outs. When hitting also wins chips later, the implied odds allow some calls below the price.
Keep going
- Practice with real prices: the pot odds quiz.
- One spot every day: the daily poker puzzle.
- When hitting costs more than it pays: reverse implied odds.
- Exact numbers for a common case: flush draw vs top pair.
- The straight version: open-ended straight draw vs overpair.
- What a draw that bets is worth: fold equity.
- When the "4" only counts if you see the river: equity realization.
- Draws that need the turn and the river: backdoor draws.
All of these reference numbers fit on one page in our poker cheat sheet.
Sources
- Every exact percentage on this page is computed by counting the unseen cards, checked on October 10, 2026.
- The answer to the spot follows rules written by the app's author; it does not come from a solver.