What this calculator does
Working out an exact poker win probability requires simulating every possible way the remaining cards could come out, weighed against every hand an opponent might hold, which is a genuinely complex calculation that depends on information a player at the table rarely has in full. What players actually use during a hand is a much simpler, well-known shortcut: the rule of 2 and 4.
The rule of 2 and 4 estimates win probability from your number of outs, the cards left in the deck that would improve your hand to a likely winner. After the flop, with two cards still to come, multiply your outs by 4. After the turn, with one card left, multiply by 2. It is a genuine, published approximation used at real poker tables, not an exact equity calculation, and this calculator is built around that specific, honestly-scoped heuristic rather than pretending to simulate full hand equity.
The formula
Count your outs: the cards remaining in the deck that would complete your hand into what you believe is likely to be the best hand. Multiply that count by 4 if two cards are still to come (after the flop), or by 2 if only one card is left (after the turn), to get an approximate percentage chance of winning.
| Term | Meaning |
|---|---|
| Outs | The number of remaining cards that would improve your hand to a likely winner. |
| Rule of 4 | Outs × 4, used after the flop when two community cards are still to come. |
| Rule of 2 | Outs × 2, used after the turn when one community card is still to come. |
The inputs explained
| Field | What to enter |
|---|---|
| Number of outs (cards that improve your hand) | The number of cards left in the deck that would give you a likely winning hand. |
| Stage | Whether you are calculating after the flop (two cards to come) or after the turn (one card to come). |
When to use it
Deciding whether to call a bet on the flop
Counting outs after the flop and applying the rule of 4 gives a quick estimate of your winning chances, which can then be weighed against the size of the bet you are being asked to call.
Reassessing on the turn
Once the turn card is revealed, only one card remains, so the same outs count is now multiplied by 2 rather than 4, roughly halving the earlier flop-stage estimate.
Learning the shortcut instead of memorising exact percentages
The rule of 2 and 4 is popular precisely because it is fast enough to use during a hand, trading a small amount of accuracy for a calculation that can be done in your head at the table.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Approximate win probability by number of outs, flop versus turn
A range of out counts, compared at the flop stage and the turn stage.
Questions
Is the rule of 2 and 4 exact?
No, it is a heuristic approximation, not an exact equity calculation. It is reasonably close for outs up to about 8, but becomes increasingly optimistic with more outs, which is why this calculator flags a lower-accuracy note above that threshold. A full equity calculation would need to simulate every remaining card combination against a range of opponent hands.
What counts as an out?
An out is any remaining card in the deck that would complete your hand into what you judge to be the likely winner. Counting outs accurately, and not double-counting cards that help an opponent just as much as you, is the main skill involved; the rule of 2 and 4 itself is just the multiplication step afterwards.
Why does the flop use 4 and the turn use 2?
Each out has roughly a 2% chance of appearing on any single remaining card. With two cards still to come after the flop, that is roughly outs × 2 × 2 = outs × 4; with only one card left after the turn, it is just outs × 2.
Why does this calculator warn about high out counts?
The rule of 2 and 4 is a linear approximation of what is actually a slightly curved relationship, and it overstates win probability once outs climb much past 8, particularly at the flop stage with two cards to come. Above that point, treat the result as a rough upper-end guide rather than a precise figure.
For the underlying probability concepts behind heuristics like this one, see the general probability calculator.