Advantage Play & Game Integrity
Blackjack card counting
Blackjack card counting is a technique where a player tracks the ratio of high to low cards already dealt to estimate whether the remaining deck favours the player or the dealer.
Key points
- Card counting tracks exposed cards to estimate when the remaining deck is rich in tens and aces, which favours the player.3
- A positive running count means more small cards have been played; the true count adjusts for the number of decks left.4
- Counters vary bet size and sometimes playing decisions based on the true count to gain an edge of up to about 2%.2
- Card counting is not illegal under UK or US law unless an external device or another person assists the player.1
How to count cards with the Hi-Lo system
- Assign +1 to cards 2 through 6, 0 to 7–9, and −1 to 10, jack, queen, king and ace.3
- Keep a running count by adding or subtracting the value of each card as it is dealt.
- Divide the running count by the number of decks remaining to get the true count.4
- When the true count is positive, increase your bet; when negative or zero, bet the minimum.
- Use basic strategy adjusted for the true count to make playing decisions.
Example with one deck
In a single-deck game, you see the first hand: 5 (+1), 3 (+1), 10 (−1), 7 (0), ace (−1). Your running count is 0. With 0.75 decks left, the true count is 0 ÷ 0.75 = 0, so no bet change. Later, after seeing many small cards, the running count is +6 with half a deck left: true count = +6 ÷ 0.5 = +12, a strong signal to raise your bet.
Common questions
How does blackjack card counting work?
The player keeps a running count of high and low cards dealt, converts it to a true count by dividing by decks remaining, and uses that number to decide when to bet more (positive count) or less (negative count).3
How to count cards in blackjack?
Assign +1 to 2–6, 0 to 7–9, and −1 to 10–A. Keep a running total as each card appears. Divide by the number of decks left to get the true count. Bet more when the true count is positive.3
How to count cards in blackjack with 6 decks?
Use the same Hi-Lo values. After each round, divide your running count by the estimated number of full decks remaining. For example, a running count of +12 with 3 decks left gives a true count of +4.4
How do you count cards in blackjack with one deck?
With one deck, the running count and true count are the same until cards are dealt. Track each card's value (+1, 0, −1). A running count of +6 with half a deck left means a true count of +12.3
Where this term is used
Not the same as
- Blackjack odds with card counting — the outcome or effect of counting on expected value, not the counting method itself
- Card counting machine blackjack — a device or table that may assist counting, whereas card counting is a player strategy
Related terms
Sources
- Card counting en.wikipedia.org Provides the core definition, legal status, and distinction from illegal assistance.
- Blackjack en.wikipedia.org Supports the house edge range and the player edge from counting.
- Card Counting in Blackjack - Introduction & Basics wizardofodds.com Explains the Hi-Lo system values and the running count method.
- Introduction to the High-Low Card Counting Strategy wizardofodds.com Describes the true count formula and its use in betting decisions.
Sources are drawn from regulators, universities and published research, and each one is labelled with what it actually is — a preprint is not called a paper. Bookmaker and affiliate pages are never cited here, because a page that sells betting is not a neutral authority on it.