What this calculator does
Roulette odds are fixed, published mathematics: every bet type has an exact win probability and payout that never changes from spin to spin, since each spin is an independent, equally-likely event across every pocket on the wheel. This calculator shows the win probability, payout odds and resulting house edge for the two simplest and most common bet types, on either wheel variant.
The house edge comes from the payout being set slightly below what a truly fair bet would pay. A fair straight-up bet on a 37-pocket wheel would pay 36:1 to exactly break even over time; casinos pay 35:1 instead, and that single unit of difference is where the house edge comes from.
The formula
Win probability for a straight-up bet is 1 divided by the number of pockets on the wheel. For an even-money bet (red/black, odd/even, high/low) it is 18 divided by the number of pockets, since 18 of the non-zero pockets fall on each side of those bets. House edge is calculated as 1 minus the win probability multiplied by (payout + 1), which captures how far the actual payout falls short of a mathematically fair one.
| Term | Meaning |
|---|---|
| European wheel | A roulette wheel with 37 pockets: numbers 1-36 plus a single zero. |
| American wheel | A roulette wheel with 38 pockets: numbers 1-36 plus both a single zero and a double zero. |
| House edge | The built-in percentage advantage the casino holds on a bet, representing the average proportion of each bet lost over many repeated bets. |
The inputs explained
| Field | What to enter |
|---|---|
| Wheel | Choose European (single zero, 37 pockets) or American (single and double zero, 38 pockets). |
| Bet type | Choose a straight-up bet on a single number, or an even-money bet such as red/black. |
When to use it
Comparing European and American wheels
The extra double-zero pocket on an American wheel doesn't change the payout odds, but it does lower win probability and roughly double the house edge, since there are more losing pockets for the same fixed payout.
Understanding why house edge exists at all
Seeing the exact win probability against the exact payout shows precisely where the house's advantage comes from: the payout is set slightly below what true, fair odds for that probability would require.
Checking a bet before playing
Knowing the house edge on a specific bet type and wheel variant beforehand is a factual, mathematical reference point, independent of any particular session's results.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does house edge compare between European and American wheels?
The house edge for each combination of wheel and bet type.
Questions
Why is the house edge the same for every simple bet on a European wheel?
Because every straight-up and even-money bet on a European wheel pays out at exactly the rate that produces the same 2.70% house edge; only certain unusual bets (like the "five number" bet, only available on American wheels) have a different edge.
Is a European wheel always better for the player?
For the same simple bet types, yes: fewer total pockets for the same payout gives a lower house edge, which is why a European (single-zero) wheel is generally more favourable to players than an American (double-zero) wheel.
Does house edge guarantee a specific result on any one spin?
No. House edge is a long-run average across many repeated bets; any single spin is still entirely random, and short-term results can and do vary widely from the mathematical average in either direction.
What does "35:1" payout actually mean?
It means a winning bet returns 35 times the amount staked, plus the original stake back, for a total return of 36 times the bet. A truly fair payout for a 1-in-37 chance would need to return 36 times the stake in winnings alone (37 times total) to break even over time.
For a different kind of odds-from-probability calculation, see the implied probability calculator.