Where the roulette house edge comes from
Roulette payouts are set as if the wheel had 36 pockets, but a single-zero wheel has 37 and a double-zero wheel has 38. That gap is the edge: 1/37 (about 2.70%) on a single-zero wheel and 2/38 (about 5.26%) on a double-zero wheel, on almost every bet. No pattern of bets changes it.
The wheel has one pocket too many
A single-zero wheel carries the numbers 1 to 36 plus a green 0, so 37 pockets in all. A double-zero wheel adds a 00 and has 38. Every pocket is equally likely on a sound wheel or a tested generator.
The payouts ignore the green pockets. A bet on one number pays 35 to 1, which would be exactly fair if there were 36 pockets. With 37, the true odds against you are 36 to 1, and the difference is kept by the house. This is the simplest working example of house edge and RTP.
The calculation for a single number
Stake one unit on a single number on a single-zero wheel. One pocket in 37 wins 35 units; the other 36 lose the unit.
(1/37 × 35) − (36/37 × 1) = −1/37 ≈ −2.70%
The result is the bet's expected value: on average, each unit staked loses 1/37 of itself. On a double-zero wheel the same sum gives (1/38 × 35) − (37/38 × 1) = −2/38, about −5.26%.
Every standard bet has the same edge
All the regular bets follow one pattern. A bet covering n numbers pays (36/n) − 1 to 1, so the return including the stake is always 36/37 of the amount wagered on a single-zero wheel.
| Bet | Numbers covered | Pays | Chance of winning (single zero) | House edge (single zero) | House edge (double zero) |
|---|---|---|---|---|---|
| Straight up | 1 | 35 to 1 | 2.70% | 2.70% | 5.26% |
| Split | 2 | 17 to 1 | 5.41% | 2.70% | 5.26% |
| Street | 3 | 11 to 1 | 8.11% | 2.70% | 5.26% |
| Corner | 4 | 8 to 1 | 10.81% | 2.70% | 5.26% |
| Six line | 6 | 5 to 1 | 16.22% | 2.70% | 5.26% |
| Dozen or column | 12 | 2 to 1 | 32.43% | 2.70% | 5.26% |
| Red/black, odd/even, high/low | 18 | 1 to 1 | 48.65% | 2.70% | 5.26% |
The table shows why "covering the board" does not help. Spreading chips over many numbers raises the chance that something wins and lowers what the win is worth, in exact proportion. A combination of bets is a sum of bets, and each part carries the same margin.
Two exceptions worth knowing
The five-number bet on a double-zero wheel. A bet on 0, 00, 1, 2 and 3 pays 6 to 1. Five winning pockets returning 7 units each gives 35/38, so the edge is 3/38, about 7.89%. It is the most expensive regular bet on that wheel.
Half back on zero. Some single-zero tables return half of an even-money stake when the ball lands on 0. On those bets the loss on zero is half a unit, and the edge becomes 1/74, about 1.35%. The rule applies only if the table's displayed rules say so.
Why doubling up fails
The Martingale system says: bet on an even-money chance, double the stake after every loss, and the first win recovers everything plus the base stake. The flaw is the size of the stake a losing run demands.
Base stake KES 20 on red, single-zero wheel, doubling for up to ten spins. The tenth stake is KES 10,240 and the total at risk is KES 20,460.
Ten losses in a row have a probability of (19/37) multiplied by itself ten times, about 0.13%, or roughly once in 784 sequences. The sequence wins KES 20 the rest of the time. Averaged out: (99.87% × 20) − (0.13% × 20,460) ≈ −KES 6.11 per sequence.
That KES 6.11 is exactly 1/37 of the average total staked in the sequence. The system rearranges the losses into one rare large one; it does not remove them. Other progressions do the same thing in a different shape, as the guide to the gambler's fallacy and session limits explains.
Hot numbers, cold numbers and the results board
Tables and game screens often show recent results and "hot" or "cold" numbers. The board is accurate history and useless forecasting. A fair wheel has no memory, so each pocket has a 1 in 37 chance on every spin whatever came before.
In any short list of spins some numbers will appear several times and others not at all. That unevenness is what randomness looks like in a small sample. Seeing a pattern in it is a habit of the human eye, not a property of the wheel.
What an hour costs
The price of roulette is the edge multiplied by the total staked. More spins and bigger stakes mean a higher average cost, win or lose on the night.
Forty spins at KES 100 a spin is KES 4,000 staked. On a single-zero wheel the expected loss is 4,000/37, about KES 108. On a double-zero wheel it is 4,000 × 2/38, about KES 211.
Software roulette can run many more rounds per hour than a physical wheel, and the cost scales with the count. The results of a software wheel come from a random number generator rather than a ball.
What the rules in Kenya require a table to show
Regulation 20(2) of the Gambling Control (Conduct of Gambling Operations) Regulations, 2026 requires a licensee to "display clearly rules of games, odds, house edge and average return to the player". Regulation 20(1) says casino games "must be authorized by the Authority", and regulation 19 requires closed circuit television in the areas where gaming takes place.
For a player this means the number of zeros, the payouts and any half-back rule should be readable before a stake is placed. If the edge shown differs from 1/37 or 2/38, the rules will say which variant is in use. Roulette is compared with a game where decisions matter in the guide to the blackjack house edge.
Questions and answers
Which roulette bet has the lowest house edge?
On a single-zero wheel every standard bet has the same edge, 1/37 or about 2.70%. The exception is a table that returns half of an even-money stake when zero lands: on those bets the edge falls to 1/74, about 1.35%. Check the rules displayed at the table.
Why is double-zero roulette worse for the player?
The payouts are the same as on a single-zero wheel, but there is one more losing pocket. The edge rises from 1/37 to 2/38, from about 2.70% to about 5.26%, so the same stakes cost almost twice as much on average.
Does the Martingale system work on roulette?
No. Doubling after each loss produces frequent small gains and a rare loss large enough to cancel them and more. The expected loss stays at the house edge multiplied by the total amount staked, and table limits and balances stop the doubling sooner or later.
Are numbers that have not come up for a while more likely to land?
No. Each spin is independent. A number absent for a hundred spins has the same chance on the next spin as any other pocket: 1 in 37 on a single-zero wheel.
Is online roulette different from a live wheel in its maths?
The payout table and the number of pockets decide the edge, so the arithmetic is the same. What differs is how the result is produced: a physical wheel in a live game, a random number generator in a software game.