En prison rule in roulette

How the en prison rule works, spin by spin

"En prison" is French for "in prison", and the name describes the mechanism well. On a normal single-zero table, zero beats every even-money bet outright. Under en prison your bet on red, black, odd, even, 1–18 or 19–36 is not taken when zero lands; it is moved into a holding position, often shown on the line around the even-money box, and stays there for the next spin.

What happens next depends entirely on that following spin. The Wizard of Odds roulette basics page (opens in a new tab) puts it simply: if the imprisoned bet wins, the stake is released and returned, but without any winnings. If it loses, the house collects. The Wikipedia roulette article (opens in a new tab) describes the rule the same way.

So the best you can do with an imprisoned bet is break even. En prison is a second chance to get your money back, not a second chance to win.

Single or double imprisonment: when zero lands again

The awkward case is a second zero while your bet is already in prison. Casinos handle it in different ways, and Wizard of Odds notes both versions exist:

• Single imprisonment. A second zero loses the imprisoned bet. This is the simpler and slightly dearer version for the player.
• Double (repeated) imprisonment. A second zero sends the bet further into prison rather than losing it outright. The exact conditions for getting it back then vary by table, so read the rules screen.

Zero twice in a row happens about once in 1,369 spins (37 × 37), so this detail moves the price only a little. It is still worth checking, because it is the kind of rule that is easy to assume and hard to argue about after the fact.

En prison rule maths and house edge

To see where the edge comes from, value the imprisoned bet first and then fold it back into the whole bet. This uses a 1-unit stake and single imprisonment.

1. Once imprisoned, the next spin releases the stake on 18 of 37 numbers (worth 0, since you only get your unit back) and loses it on the other 19 (18 wrong-colour numbers plus zero). The imprisoned bet is worth 19/37 of a unit lost, about −0.514.
2. Now take the original spin. Your bet wins +1 on 18 numbers, loses −1 on 18 numbers, and becomes the imprisoned bet on zero.
3. Add it up over 37 spins: +18 − 18 − 19/37 = −19/37 of a unit.
4. Divide by 37 to get the average per spin: −19/1,369, which is −1.388%. That matches Wizard of Odds' figure of −1.387874% for single imprisonment.

With repeated imprisonment the same source gives −1.370117%. Both compare with −1.351351% under La Partage and −2.70% on a standard European roulette table. The reason en prison is a fraction worse than La Partage sits in step 1: an imprisoned unit is worth −0.514 on average, while La Partage simply fixes the zero loss at −0.5.

What en prison costs per spin and per hour

Turning the percentages into pounds shows how close en prison is to La Partage, and how far both are from a standard table. Expected loss is simply stake times edge.

Over 500 spins at £20, the difference between single imprisonment and La Partage is under £4 on £10,000 staked. The difference between either rule and a plain single-zero table is more than £130. If you want lower-cost roulette, the rule matters far more than which of the two French rules you get. These are averages; real results swing much more than these gaps in the short run.

How to play an en prison bet step by step

1. Before betting, open the table's rules screen and confirm it says "en prison" for even-money bets on zero, and how a second zero is treated.
2. Place your stake on red, black, odd, even, 1–18 or 19–36. Only these qualify.
3. If zero lands, leave the imprisoned chip where the game puts it. At some tables you may be offered a choice between imprisonment and taking half back; read the prompt carefully.
4. Watch the next spin. A win for your bet returns the stake to your balance with no winnings; a loss or (under single imprisonment) another zero removes it.
5. Keep in mind your money is committed for an extra round, so count it as still on the table when you check your budget.

Where a table offers the choice between losing half and imprisonment, Wizard of Odds says the expected value comes out the same under French rules. Otherwise, losing half straight away is slightly cheaper. Either way, the choice only arises on zero, about once every 37 spins.

Where the en prison rule turns up

En prison belongs to the French tradition and is associated with French roulette, alongside La Partage. Online, the rule you see named is often La Partage instead: Evolution's live roulette range (opens in a new tab), for example, lists its French Roulette with La Partage. We have not confirmed which UK online tables use en prison, so the only reliable check is the help screen of the specific game.

Neither rule appears on a standard American roulette table, and neither helps inside bets, dozens, columns or call bets. Those all keep the full single-zero edge of 2.70% on a French table.

Do not assume a table uses en prison because its layout carries French names such as rouge, noir, pair, impair, manque and passe. The labels are presentation; the zero rule is set in the game's rules screen.

En prison myths and misreadings

• "An imprisoned bet can win double." It cannot. The best result is getting your stake back.
• "Zero won't come up twice, so prison is a sure release." The next spin is a fresh 18 in 37 chance, under half. Your bet is more likely to be lost than released.
• "En prison is better than La Partage because you might get everything back." Averaged out, the half you keep under La Partage is worth slightly more than the 48.65% chance of a full release.
• "After zero, the other colour is due." Spins are independent events; the wheel has no memory, and the gambler's fallacy explains why that idea persists.
• "A lower edge means I will come out ahead over time." A 1.37–1.39% edge still makes losses the likely result over many spins.

En prison and UK online roulette rules

Whatever zero rule a table uses, UK design rules shape how it plays online. The Gambling Commission's responsible product design standard (opens in a new tab) requires at least 5 seconds between game cycles for casino games other than slots, bans autoplay (a re-bet button is allowed), stops you playing several games at once and requires net spend and time played to be shown on screen. The online slot stake limits do not cover roulette. Our page on UK game speed rules explains the timings.

A held stake can make your balance look lower than your real position for a spin, so keep an eye on the session total the game displays. If you want firm boundaries, a deposit limit is the simplest tool, and the National Gambling Helpline on 0808 8020 133 is available around the clock.

Where to play roulette with en prison rules

To find an en prison table, browse the French roulette games in a UK-licensed casino's lobby and confirm the rule in each game's help screen. We have not checked which tables our partners run, so check the casino's game lobby.

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