Blackjack › Questions › Card counting
How does card counting work in blackjack?
You keep a running tally of the cards you see. With Hi-Lo, every 2 to 6 adds one, every ten and ace subtracts one, and 7 to 9 count nothing. A high count means the cards left are rich in tens and aces, which favor the player, so you bet more; a low count favors the dealer, so you bet the minimum.
Hi-Lo per deck: 20 cards count +1, 12 count 0 and 20 count −1, so a whole deck ends at exactly 0.
The Hi-Lo tags
Every card gets a tag. You add them as the cards come out and keep the total in your head: that total is the running count.
| Card | Tag |
|---|---|
| 2 | +1 |
| 3 | +1 |
| 4 | +1 |
| 5 | +1 |
| 6 | +1 |
| 7 | 0 |
| 8 | 0 |
| 9 | 0 |
| 10 J Q K | −1 |
| A | −1 |
Why
Cards dealt from a shoe do not come back until the shuffle, so what is left changes as the shoe goes. Tens and aces help the player: a blackjack pays 3 to 2, doubles on 10 and 11 hit big, and a dealer who must hit 12 to 16 busts more often. Low cards help the dealer, who makes hands out of stiff totals with them. The count tracks which way the shoe has drifted, and the player raises the bet only when it has drifted in their favor. It does not predict the next card; it only says what the deck is made of now.
From running count to true count
In a shoe the running count has to be divided by the decks still to be dealt, because +6 with one deck left says much more than +6 with five decks left. That per-deck figure is the true count, and it is what the betting and the strategy changes are keyed to.
Betting with the count
Counters bet the table minimum at a true count of +1 or lower and raise the bet as the true count climbs, typically to 8 or 12 times the minimum at +5 or more. Most of the edge comes from the bets, not from the strategy changes. A handful of plays also change with the count, the best known being insurance, which becomes worth taking at a Hi-Lo true count of +3.