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How to count cards in blackjack

Card counting is simple maths: you keep a running tally of the cards you've seen so you know when the cards left in the shoe favour you. This guide teaches the Hi-Lo system, the most widely used count, and gives you a plan to practise it.

Why counting works

Blackjack is unusual among casino games because the cards aren't replaced after each hand. When lots of low cards have been dealt, the remaining shoe is rich in tens and aces. That helps the player: blackjacks (which pay 3:2) come more often, doubles on 10 and 11 land more often, and the dealer, who must hit stiff hands like 12 to 16, busts more. When the remaining cards are mostly low, the dealer benefits instead. Counting tells you which situation you're in.

Step 1: learn the Hi-Lo values

There are 20 low cards, 12 neutral cards and 20 high cards in a deck, so a full deck always adds up to zero. That gives you a built-in check when you practise.

Step 2: keep a running count

Start at 0 after every shuffle and add or subtract for each card you see, including other players' cards and the dealer's. For example, if the cards 5, K, 3, 9 and 2 come out, the running count is +1 −1 +1 +0 +1 = +2.

The trick that speeds people up is cancelling pairs: a low card and a high card together are 0, so you can ignore them. Good counters look at a whole hand at once rather than card by card.

Step 3: convert to a true count

Casinos use shoes of 6 or 8 decks, so a running count of +6 means much more with 1 deck left than with 5. Divide the running count by the number of decks still to be dealt to get the true count:

Step 4: bet with the count

The advantage comes from betting more when the true count is high. A simple ramp is to bet your minimum at a true count of +1 or below, then 2 units at +2, 4 units at +3 and 8 units at +4 or higher. Each true count point is worth roughly half a percent of advantage, so at +1 you are only around break-even.

Step 5: adjust a few plays

Once betting is automatic, learn the Illustrious 18: a short list of hands where the count changes the correct play, such as standing on 16 against a 10 at a true count of 0 or higher.

A practice plan that works

1. Basic strategy first. Counting is worthless if you misplay hands. Use the basic strategy chart and the strategy quiz until you score 95% or more.
2. Count a single deck. Turn cards over one at a time and aim to get through a full deck in under 30 seconds with no mistakes. The trainer's count drill times you and can secretly remove cards so you can't just assume the answer is 0.
3. Practise true counts. Use the true count drill to get fast at dividing by decks remaining.
4. Put it together. Play full shoes in the Play mode with pretend chips, keeping the count while you play and size your bets.
5. Add deviations. Drill the Illustrious 18 in the drill library.

Be realistic

Even played perfectly, counting gives a small edge (often quoted as around 0.5% to 1.5%) with large swings, so you need a sizeable bankroll. It is useless against continuous shuffling machines, and tables that pay 6:5 for blackjack wipe out the edge. Counting in your head isn't illegal in most places, but casinos are private businesses and can limit your bets or ask you to leave. Using a device to help you count is illegal in many places.

Frequently asked questions

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