Does Card Counting Work Online?

Against most online blackjack, no: the computer reshuffles the deck before every hand, so there is nothing to count. It can work in games that deal from a shoe for many rounds before reshuffling, like live-dealer tables and some multiplayer games. Even then the gain is small. In our 20 million simulated hands, a Hi-Lo counter betting 1 unit normally and up to 8 units when the count is high turned a 0.51% house edge into a 0.38% player edge.

Why counting works at all

Blackjack is dealt without replacement. Once a card is out, it's out until the next shuffle. Tens and aces are good for you: they make blackjacks, which pay 3 to 2, and they bust the dealer's stiff hands. Low cards help the dealer, who has to hit 12 to 16. So a shoe with more high cards left than usual is, briefly, a shoe that favors the player.

The idea was published by mathematician Edward Thorp in Beat the Dealer (1962), building on the basic strategy calculated by Roger Baldwin and three colleagues in 1956. Our short history of blackjack covers the story.

How the Hi-Lo count works

Hi-Lo is the most widely taught system, because it's simple:

Start at 0 after a shuffle and add the value of every card you see. That's the running count. Divide it by the number of decks left in the shoe and you have the true count. A true count of +2 means about two extra high cards per remaining deck.

What the count is worth

We sorted 20 million simulated hands, played with perfect basic strategy in a 6-deck shoe dealt until 52 cards remain, by the true count at the start of each hand.

Roughly, each point of true count moves your expectation by half a percent. The player has the edge in only about 28% of hands. The rest of the time the house is ahead.

Turning a count into an edge

Knowing the count isn't enough; you have to bet more when it's good. Our results with three betting plans:

That's the whole prize: well under 1% of what you bet, after hours of perfect counting and perfect strategy. It also comes with huge swings, because your biggest bets land in a small share of hands. Professional counters in casinos also adjust their playing decisions by count, which adds a little more, and they have to hide what they're doing, because casinos can refuse their bets.

Where counting can't work

• Standard online blackjack. The deck is effectively reshuffled before every hand. The count is always 0.
• Continuous shuffling machines in land casinos, which return cards to the shoe after every round.
• Shoes shuffled early. If half the shoe is cut off, high counts rarely happen.

Where it can

• Live-dealer and multiplayer games that deal a physical or virtual shoe deep before reshuffling.
• Any game where you can see every card dealt from the shoe, including other players' cards.

If you want to know whether a game reshuffles every hand, its rules page should say. If it doesn't say, assume it does.

Is counting cheating?

No. Counting is just remembering cards that were shown face up. In land casinos it isn't illegal, though casinos can ask a counter to stop playing blackjack. Using a device or software to count for you is a different matter and is banned in casinos in many places.

Common questions

Does counting help with insurance? Yes, it's the one time insurance is worth taking: at a true count of about +3 or more. See Should you take insurance?

Do I need a great memory? No. You keep one number, not a list of cards. The hard part is doing it fast while playing perfect basic strategy.

Is it worth learning? As a puzzle, absolutely. As a way to make money, the edge is small, the swings are large, and most online games make it impossible.

You can practice keeping a running count while you play at a free table in the lobby.