Understanding the Roulette House Edge

House edge is the expected loss as a fraction of the amount wagered, under stated rules. It is not the fraction of spins the casino wins, and it does not predict exactly what one player will lose. For a fair single-zero straight-up bet, one of thirty-seven outcomes wins. A winning one-unit wager returns thirty-six units including the stake. The expected return is thirty-six divided by thirty-seven; subtract one unit staked and the expected net result is minus one over thirty-seven. That is a house edge of about two point seven percent. Standard ordinary red or black, dozens and other bets have different win frequencies and payouts, but the same single-zero edge. A higher chance of a small win does not remove the expected loss. Ordinary double-zero bets generally have a two-over-thirty-eight edge, about five point two six percent. The five-number basket paying six to one is an exception, with three over thirty-eight, about seven point eight nine percent. Half-back zero rules can reduce the edge on eligible even-money wagers only. They are not guaranteed by a country or game label. Apply the edge to total turnover, including money wagered again. At a hypothetical one thousand dollars of single-zero turnover, the expected loss is about twenty-seven dollars and three cents. Actual results can differ greatly. Set a limit; do not treat an average as a promised session result.