La Partage & En Prison Roulette
How French zero rules reduce the cost of even-money roulette bets.
La Partage returns half of an eligible even-money wager when zero lands, reducing the single-zero edge from 1/37 to 0.5/37, or about 1.35%. En Prison can produce equivalent long-run economics when the imprisoned-bet rule is implemented in the standard way.
La Partage
On zero, half of an eligible even-money bet is returned and half is lost. The expected loss attributable to zero is therefore halved.
The arithmetic
0.5 ÷ 37 = 0.0135135, or about 1.3514%. That compares with 1 ÷ 37 = 2.7027% on ordinary single-zero bets.
En Prison
Instead of immediately losing the wager on zero, the bet can remain “in prison” for a subsequent spin under the table rules. Exact handling should be checked because implementations can differ.
Eligible bets
Typically the rule is relevant to even-money wagers: red/black, odd/even and high/low. Do not assume it applies to dozens, columns or inside bets.