Stand only against a dealer 4, 5 or 6. Hit everywhere else.
That includes hitting against a dealer 2 and 3 — the cell most players get wrong.
Twelve only wins when the dealer breaks
Stand on 12 and any dealer total from 17 to 21 beats you. In other words, 12 wins only when the dealer busts. There is no path to winning on your own cards.
So the decision reduces to one comparison: how often the dealer busts against how often drawing keeps you alive.
Hitting busts you 31% of the time
Any card of six or more busts a 12. Sixteen of 52 cards are ten-value, so that is roughly 31%. The other 69% leave you somewhere between 13 and 21, and many of those give you another decision to make.
The difference between a 2 and a 4
This is the whole argument.
| Upcard | Busts | Survives | Play 12 |
|---|---|---|---|
| 2 | about 35% | about 65% | H Hit |
| 3 | about 37% | about 63% | H Hit |
| 4 | about 40% | about 60% | S Stand |
| 5 | about 43% | about 57% | S Stand |
| 6 | about 42% | about 58% | S Stand |
| 7 and up | 26% or less | 74% or more | H Hit |
A dealer 2 is weak, but it still survives 65% of the time. Writing off all of that to wait on a 35% bust is worse than accepting a 31% risk to build a hand that can win on its own.
Once the dealer shows 4, 5 or 6, bust probability passes 40% and the arithmetic reverses. Waiting now wins.
The margin is thin
The gap between hitting and standing on 12 against a 2 is very small. That is why instinct says stand, and why so many players do. Over a single hand you cannot tell the difference — over a few thousand hands you can.
From 13 up, you stand against a 2 as well
On 13 the busting range widens to any five or higher, so the bust probability climbs. That is why 13, 14, 15 and 16 all stand against the full 2–6 range.
Twelve is the single exception that hits against 2 and 3, because its busting range — six or more — is the narrowest.
A soft 12 is a different hand
Ace plus ace is soft 12, but the answer there is split. A pair of aces is always split whatever the dealer shows; see the splitting section of Why the Chart Works.
Soft hands built from an ace and another card also play nothing like hard hands. They cannot bust, so they play far more aggressively.