Math Friday · Outs & River Odds
The Rule of 4 and 2
A fast shortcut for draws. Not the exact answer.
The shortcut
on the flop, by the river
≈ outs × 4%
on the turn, on the river
≈ outs × 2%
An approximation. Good enough at the table.
Shortcut vs maths
Flop → river
| Draw | Outs | Rule | Exact |
|---|---|---|---|
| Gutshot | 4 | 16% | 16.5% |
| Open-ended | 8 | 32% | 31.5% |
| Flush draw | 9 | 36% | 35% |
| Flush + open-ended | 15 | 60% | 54.1% |
Exact assumes you see both cards and every out wins.
Where it breaks
With 15 outs the rule says 60%. The real number:
54.1%
The more outs you have, the more the shortcut overshoots.
Takeaway
Shortcut at the table. Maths at home.
Educational content. 18+. Play responsibly.