How to count cards in blackjack
Quick answer: card counting means keeping a running tally of the cards dealt so you know when the remaining deck is rich in high cards, which favor the player. In Hi-Lo, 2–6 count +1 and tens and aces count −1. It’s legal, but the edge is small, it demands real discipline, and it doesn’t work online.
Why counting works
Unlike roulette, blackjack has memory: dealt cards don’t go back into the shoe until the next shuffle, so what’s left changes from hand to hand.
When the remaining cards are rich in tens and aces, the player gains: more blackjacks (paid 3 to 2), better doubles, and a dealer forced to hit 16 busts more often. When they’re rich in small cards, the opposite happens. Counting simply tracks that balance.
The Hi-Lo system step by step
Hi-Lo is the most popular system because it’s simple and almost as effective as complex ones. Every card you see gets a value:
| Cards | Hi-Lo value |
|---|---|
| 2, 3, 4, 5, 6 | +1 |
| 7, 8, 9 | 0 |
| 10, J, Q, K, A | −1 |
Start at 0 after the shuffle and add the value of every card you see — yours, other players’ and the dealer’s. That number is the running count. A positive count means more low cards have gone, so more high cards remain.
Example: 5, K, 3, 9, 2, A → +1 −1 +1 0 +1 −1 = +1.
Pro tip: cancel pairs. A 5 and a king together are 0, so you can skip them and count faster.
Try it: count these cards
2–6 count +1, 7–9 count 0, tens, faces and aces count −1.
The true count
A running count of +6 means something very different with one deck left than with five. So you convert it into the true count: running count divided by decks remaining.
- Running count +6, three decks left → true count +2.
- Running count +6, one deck left → true count +6.
You estimate decks remaining by eyeballing the discard tray. Rounding to the nearest half deck is plenty.
What to do with the count
- Size your bets. This is where almost all the edge comes from. At a true count of +1 or less, bet the minimum; from +2 up, raise your bet progressively. As a rule of thumb, each point of true count moves the edge about half a percent in your favor.
- Deviate from basic strategy. At very high or low counts a few plays change. The best-known one is insurance, which becomes correct at a true count of +3 or higher. These deviations are called index plays; the 18 most valuable are the “Illustrious 18”.
Reality check: what it’s worth
This is where most guides oversell. The honest version:
- The edge is small. With good rules and deep penetration, a skilled counter might get roughly 0.5–1% on money wagered.
- The swings are huge. With that edge you can lose for weeks. You need a large bankroll to survive it.
- Casinos fight back. They shuffle early, cap your bet spread or ask you to leave.
- It doesn’t work online. RNG blackjack reshuffles every hand, and live-dealer shoes are cut too early to matter.
- Continuous shuffling machines put cards back after each hand — counting is useless against them.
Counting is a fascinating mental skill and the best way to truly understand the game. It is not an easy way to make money, and anyone saying otherwise is selling something.
Is it legal?
Counting in your head is legal — nobody can ban you from thinking. Using help is not: phones, notes, devices or signals with accomplices.
Casinos don’t have to like it, though. In most jurisdictions they can refuse service: ask you to stop playing blackjack or to leave. (New Jersey is a notable exception, where casinos can’t bar counters but can still shuffle early or limit bets.) In practice, shuffling up or limiting your bets is what usually happens first.
Before counting, master basic strategy — every strategy error costs more than the count gives back.
Frequently asked questions
Is card counting illegal?
Counting cards in your head is not illegal — you’re just paying attention. What is illegal is using devices, notes or signals with partners. Casinos, however, are private businesses: in many places (including Nevada) they can ask you to stop playing blackjack or leave.
Does card counting work online?
Not in standard online blackjack: the software reshuffles after every hand, so there is nothing to count. Live-dealer tables use a real shoe, but it’s usually reshuffled with half or more still undealt, which leaves almost no edge.
How much can you make counting cards?
Less than people think. A disciplined counter with good rules might have an edge of roughly 0.5–1% on money wagered, with huge swings — you can lose for weeks before the edge shows. That’s why very few people make it pay.
What is the true count?
The running count divided by the number of decks left to be dealt. A running count of +6 with three decks left is a true count of +2. The true count is what tells you whether the remaining cards favor you.
Do I need to know basic strategy first?
Yes. Counting without solid basic strategy is pointless: strategy mistakes cost more than the count gains. Chart first, counting second.