Why Red/Black in Roulette Isn’t 50/50: A Mathematical Breakdown

At first glance, betting on red or black in roulette feels as fair as tossing a coin. There are many red pockets, many black pockets, and the payout is 1:1. That’s exactly why the bet is so popular: it looks simple, balanced, and “safe” compared with single-number wagers. But roulette is not a coin toss, and the numbers prove it. The key reason is that roulette includes at least one green pocket that is neither red nor black. That single design choice changes the probability in a measurable way, and it doesn’t matter whether you’re playing in a physical casino, on a live dealer table, or using a standard RNG wheel. As of 2026, the two most common wheels remain the European wheel (single zero) and the American wheel (double zero), and both produce odds that are not 50/50.

What “50/50” Would Actually Mean

To call a bet “50/50”, the probability of winning must be exactly 0.5 (50%), and the probability of losing must also be 0.5 (50%). If a roulette wheel had only red and black pockets in equal numbers, then a 1:1 payout would be mathematically fair over the long run. For example, imagine a wheel with 18 red and 18 black pockets, and nothing else: you would win 18 times out of 36 on average, and lose 18 times out of 36.

However, real roulette wheels are not built that way. The European wheel has 37 pockets: numbers 1–36 plus a single green 0. The American wheel has 38 pockets: numbers 1–36 plus 0 and 00. Those extra green pockets are the reason the odds are not balanced, even though the colours are.

So the question becomes simple: how often does red (or black) appear out of the total pockets? On the wheel, there are still 18 red and 18 black, but the total is no longer 36. That difference is small in appearance, but powerful in maths.

European vs American Wheels: The Exact Probabilities

On a European (single-zero) wheel, there are 18 red pockets out of 37 total pockets. That means the probability of landing on red is 18/37, which equals about 48.65%. The probability of losing a red bet (landing on black or 0) is 19/37, about 51.35%. Black has the same numbers, so the maths is identical.

On an American (double-zero) wheel, the probability changes further. You still have 18 red pockets, but now out of 38 total pockets. The probability of red is 18/38, which is about 47.37%. Losing (black, 0, or 00) is 20/38, about 52.63%. That gap is larger than most players realise when they first look at the table.

These percentages are not theoretical curiosities; they are the real odds built into the equipment. No betting system can change that underlying ratio because every spin is independent and the wheel layout stays the same from spin to spin.

Why the Payout Makes the Bet Unfair

The next piece of the puzzle is the payout. A red/black bet pays 1:1. In other words, if you stake £10 and win, you profit £10. If you lose, you lose £10. On a true 50/50 event, that payout would be fair. But roulette is slightly worse than 50/50, so the payout is mathematically short of what would be needed for a neutral expectation.

To see the imbalance clearly, it helps to use expected value (EV). Expected value is the average profit or loss you would expect per bet if you repeated the same wager many times. In roulette, EV for red/black is negative, meaning the game is designed so the casino has an advantage in the long run.

This is also why roulette is often described as a game of “small edge, long time.” The house advantage on even-money bets looks tiny per spin, but it compounds over hundreds or thousands of spins because the probability disadvantage is always present.

Expected Value: How Much You Lose on Average

Let’s calculate EV for a £1 red bet on a European wheel. Your chance to win is 18/37, and your chance to lose is 19/37. If you win, you profit £1. If you lose, you lose £1. The EV is: (18/37 × £1) + (19/37 × -£1) = (18/37 – 19/37) = -1/37. That equals approximately -£0.027 per £1 bet, or -2.70%.

On an American wheel, the same logic gives: (18/38 × £1) + (20/38 × -£1) = (18/38 – 20/38) = -2/38 = -1/19. That equals approximately -£0.0526 per £1 bet, or -5.26%. This is why American roulette is generally considered tougher on even-money bets.

These percentages are not arbitrary. They match the house edge for roulette because the green zero pockets are the mechanism that produces it. Even though the payout “feels” symmetrical, the probability isn’t, and EV is where that reality shows up clearly.

Why Streaks Don’t “Fix” the Odds (And Why It Feels Like They Do)

Many players notice runs of red or black and feel that the wheel is “due” to switch. Others feel the opposite: that a streak means the same colour is “hot.” Both reactions are understandable, because the human brain is tuned to detect patterns, even when the process is random. But roulette spins are independent events under normal conditions.

Independence means that the probability on the next spin does not change because of what happened before. On a European wheel, red remains 18/37 every spin. It doesn’t become more likely after five blacks in a row, and it doesn’t become less likely after five reds in a row. The wheel has no memory.

The house edge is particularly effective here because it doesn’t need to do anything dramatic. The game doesn’t require the casino to “beat you” on a single session. The edge simply needs to exist consistently, and over enough spins, the average result trends toward that negative EV.

Variance, Session Results, and the Long Run

Short-term results can easily mislead. You can win five red bets in a row and feel that red is a strong choice, or lose several in a row and feel unlucky. That swing is variance: the natural fluctuation around the average. Variance is exactly why roulette can feel exciting or frustrating in a single sitting, even though the long-term maths is stable.

In practical terms, a player might have a profitable session on red/black because randomness allows it. But the expected value doesn’t disappear; it simply hasn’t had enough spins to “show” itself. Over a large number of bets, the percentage loss becomes clearer. That’s why casinos are comfortable offering even-money bets: the edge is smaller per spin, but it is reliable.

The most useful way to think about it is this: roulette doesn’t guarantee a loss every night, but it does guarantee that the average outcome is negative for the player if the bet is repeated enough times. Red/black is closer to even than many roulette bets, yet it is still mathematically tilted away from 50/50 by the presence of zero (and sometimes double zero).