Photo: Pavel Danilyuk / Pexels

Card Counting in Blackjack: How It Works and Is It Illegal?

How the Hi-Lo card counting system works, what edge it gives, why online blackjack defeats it, and where card counting is legal or a crime.

By the Gambling Hero editorial team · October 25, 2026 Industry

Card counting is a blackjack technique that tracks the balance of high and low cards left in the shoe and raises bets when the remaining cards favour players. Counting in your head is legal in the US and UK, but casinos may refuse play.

In short

The Hi-Lo count gives +1 to cards 2 to 6, 0 to cards 7 to 9 and −1 to tens and aces. Divide the running count by the decks left to get the true count, and bet more when it is high. Under current rules a realistic counter’s edge is 0.5% to 1.5%, according to the Wizard of Odds. No US or UK law bans counting with your brain, but Nevada makes counting devices a felony, and casinos can limit or bar players. In online RNG blackjack that reshuffles every round, counting has nothing to track.

How does card counting work in blackjack?

Card counting works because blackjack cards are dealt without replacement, so every card that leaves the shoe changes the odds of the next hand. When many low cards are gone, the shoe is rich in tens and aces, and that composition favours the player.

Tens and aces help the player for three reasons. They create more blackjacks, and a player blackjack usually pays 3:2 while a dealer blackjack only takes the original bet. They make the dealer bust more often, because the dealer must draw on 16 or less. They also make doubling on 10 or 11 pay off more often. A counter does not predict the next card; the count measures whether the remaining mix is good or bad.

Counting assumes perfect blackjack basic strategy; without it, playing errors outweigh the count.

How do you calculate the running count and the true count?

The running count is the sum of card values since the last shuffle; the true count divides it by the decks still to be dealt. Only the true count shows how rich the shoe is, because a running count weighs more when fewer decks remain.

The 3-step Hi-Lo method:

Tag each card. 2, 3, 4, 5, 6 = +1. 7, 8, 9 = 0. 10, J, Q, K, A = −1.
Keep a running count. Start at 0 after the shuffle; add every card seen.
Convert to a true count. Divide by the decks left, estimated from the discard tray.

Card seen	K	5	3	9	A	6	2
Hi-Lo value	−1	+1	+1	0	−1	+1	+1
Running count	−1	0	+1	+1	0	+1	+2

Worked example: in a 6-deck shoe, 2 decks have been dealt and the running count is +8. Four decks remain, so the true count is 8 ÷ 4 = +2. The same +8 with 2 decks left gives +4.

How much of an edge does card counting give?

Card counting gives a small edge. The Wizard of Odds puts a realistic advantage at only 0.5% to 1.5% under current rules, and notes that the bankroll goes “up and down like a roller coaster in the short run”.

In money terms, a counter who wagers $10,000 in total at a 1% edge expects to win $100, while short-term swings are far larger. The edge depends on the rules, deck penetration (how deep the dealer deals before shuffling) and bet spread. The Wizard of Odds warns that “more than doubling your last bet is a fast way to arouse ‘heat'”.

Editor’s insight

The 0.5% to 1.5% range is thin. One rule change can shrink or erase it: a table that pays 6:5 on blackjack instead of 3:2, a shoe cut at half its depth, or a cap on bet spreads. Before trusting any claim that counting “beats” a casino, check the blackjack payout and how deep the cards are dealt. Those two details decide whether a count has value.

Is card counting illegal?

Card counting with your own memory is not illegal in the US or the UK. Using a device to count is a felony in Nevada, and casinos may shuffle early, restrict bets or bar players they identify as counters.

Jurisdiction	Mental counting	Devices	Can casinos bar counters?
Nevada (US)	Legal	Felony under NRS 465.075	Yes, casinos may bar or restrict players
New Jersey (US)	Legal	Not covered here	Uston v. Resorts (1982): Atlantic City casinos could not bar counters without a valid Casino Control Commission regulation
United Kingdom	No statute names card counting	Cheating is an offence under s.42 Gambling Act 2005	No court ruling on counters found in the sources we read

Nevada Revised Statutes 465.075 bans devices or software that keep track of cards, analyse probability or analyse betting strategy in a licensed establishment. Under NRS 465.088, a first offence is a category C felony, and a repeat offence is a category B felony with 1 to 6 years in prison and a fine of up to $10,000 (as of October 2026). In the UK, the Supreme Court held in Ivey v Genting Casinos (2017) that edge-sorting at punto banco, worth just over £7.7 million to Phil Ivey, was cheating. The judgment does not mention card counting, and it says the label “advantage play” settles nothing.

Important

Mental counting is legal, but a device or app can make it a criminal offence; in Nevada a first offence is a felony. Check local rules in our US legal guide and UK legal guide, and remember that a 0.5% to 1.5% edge still produces long losing runs.

Can you count cards in online blackjack?

Card counting in online blackjack depends on the game type. RNG blackjack that reshuffles the virtual deck before every round leaves nothing to count. Live dealer blackjack uses real cards, but large shoes and early shuffles reduce the value of a count.

The 2-question online check:

RNG or live? An RNG game states its shuffle rule in the help screen. A shuffle every round means each hand starts from a full deck.
How many decks? A live blackjack rules sheet filed with the Nevada Gaming Control Board specifies eight pre-shuffled decks. More decks mean each card moves the true count less.

Counting software is no shortcut: Nevada’s device ban also covers games offered by a licensee or its affiliate, not only the casino floor. Our live casino section explains studio tables.

What do casinos do to stop card counters?

Casinos stop card counters with game conditions rather than laws: more decks, shallower penetration, continuous shuffling machines, limits on bet spreads and, finally, refusing to deal. The Wizard of Odds notes that casinos may go as far as barring a player.

Each countermeasure attacks one input of the edge. Earlier shuffles keep the true count low. A continuous shuffler returns cards after each round, so the shoe composition barely changes. Flat-bet requests remove the bet spread, which is how a counter turns information into money. Our responsible gambling page covers limits and help if play stops being fun.

Our take

Card counting is a real, legal technique, and that is rare in casino gambling. Our editorial view is that it is also widely oversold. The documented edge is 0.5% to 1.5%, and it needs perfect basic strategy, a 3:2 table, deep penetration and a bet spread that draws attention. For most players, the value of learning Hi-Lo is understanding why blackjack odds move during a shoe. Learn it for that reason, play basic strategy, and do not treat it as an income source. Never use a device: in Nevada that is a felony.

Key takeaways

Hi-Lo: +1 for 2–6, 0 for 7–9, −1 for tens and aces.
True count = running count ÷ decks remaining; +8 with 4 decks left = +2.
A realistic counting edge is 0.5% to 1.5% (Wizard of Odds).
Devices that track cards are a felony in Nevada; a repeat offence carries 1 to 6 years.
Ivey v Genting (2017): edge-sorting worth £7.7 million was held to be cheating.

FAQ

Is card counting illegal in Las Vegas?

No. Mental counting is legal in Nevada; using a device is a felony under NRS 465.075.

Is card counting illegal in the UK?

No statute bans it. The 2017 Ivey judgment concerned edge-sorting, which the Supreme Court held to be cheating; card counting was not addressed.

How hard is card counting?

Hi-Lo uses three values, but counting, converting and playing perfect basic strategy at speed takes long practice.

Can you count cards at baccarat?

The shoe changes, but baccarat has no drawing decisions to adjust, so the practical value is small.