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Roulette Probability Calculator

Calculate the probability of finishing ahead, ending losses and a range of final results for fixed red/black roulette bets over a chosen number of spins.

A fixed colour-bet example

Display currency

Currency labels the amounts you enter. No exchange-rate conversion is performed.

Wheel

All selected rounds are completed. The threshold does not stop play. Red/black pays 1:1; all zeros lose. No partial refunds, side bets, fees or changing stakes.

Many possible endings

Modelled mean net result

-£5.41
35.53%Probability of finishing above £0.00
5.11%Probability ending loss is at least £40.00
-£40.005th percentile of ending net result
£28.0095th percentile of ending net result
-£200.00£200.00
Gold: negative endings. Teal: zero or positive endings. Each bar represents a possible net result under the finite binomial model; this is not observed player data.
Show numerical outcome table
Net resultProbability
-£200.00<0.01%
-£196.00<0.01%
-£192.00<0.01%
-£188.00<0.01%
-£184.00<0.01%
-£180.00<0.01%
-£176.00<0.01%
-£172.00<0.01%
-£168.00<0.01%
-£164.00<0.01%
-£160.00<0.01%
-£156.00<0.01%
-£152.00<0.01%
-£148.00<0.01%
-£144.00<0.01%
-£140.00<0.01%
-£136.00<0.01%
-£132.00<0.01%
-£128.00<0.01%
-£124.00<0.01%
-£120.00<0.01%
-£116.00<0.01%
-£112.00<0.01%
-£108.00<0.01%
-£104.00<0.01%
-£100.00<0.01%
-£96.00<0.01%
-£92.00<0.01%
-£88.00<0.01%
-£84.00<0.01%
-£80.00<0.01%
-£76.000.01%
-£72.000.03%
-£68.000.06%
-£64.000.1%
-£60.000.19%
-£56.000.32%
-£52.000.53%
-£48.000.83%
-£44.001.24%
-£40.001.8%
-£36.002.49%
-£32.003.31%
-£28.004.23%
-£24.005.19%
-£20.006.12%
-£16.006.94%
-£12.007.55%
-£8.007.9%
-£4.007.94%
£0.007.67%
£4.007.13%
£8.006.36%
£12.005.46%
£16.004.5%
£20.003.57%
£24.002.72%
£28.001.99%
£32.001.39%
£36.000.94%
£40.000.61%
£44.000.38%
£48.000.23%
£52.000.13%
£56.000.07%
£60.000.04%
£64.000.02%
£68.00<0.01%
£72.00<0.01%
£76.00<0.01%
£80.00<0.01%
£84.00<0.01%
£88.00<0.01%
£92.00<0.01%
£96.00<0.01%
£100.00<0.01%
£104.00<0.01%
£108.00<0.01%
£112.00<0.01%
£116.00<0.01%
£120.00<0.01%
£124.00<0.01%
£128.00<0.01%
£132.00<0.01%
£136.00<0.01%
£140.00<0.01%
£144.00<0.01%
£148.00<0.01%
£152.00<0.01%
£156.00<0.01%
£160.00<0.01%
£164.00<0.01%
£168.00<0.01%
£172.00<0.01%
£176.00<0.01%
£180.00<0.01%
£184.00<0.01%
£188.00<0.01%
£192.00<0.01%
£196.00<0.01%
£200.00<0.01%

The percentile band contains at least 90% of modelled outcomes. Results outside it remain possible. Ending loss is different from reaching a loss limit during play.

A finite probability model

Let K be the number of winning rounds among n independent completed rounds. K follows a binomial distribution with win probability 18/37 for the single-zero example or 18/38 for the double-zero example. The probability of k wins is C(n,k) × pk × (1 − p)n−k.

The ending net result is stake × (2K − n). The model evaluates each possible number of wins, rather than generating a random sample. The calculations use floating-point arithmetic.

Read the results correctly

Finishing positive means strictly above zero. Breaking even does not count. The 5th and 95th percentiles are the first possible outcomes whose cumulative probability reaches those thresholds, so the inclusive band contains at least 90% of outcomes.

The ending-loss threshold is not a stop-loss or ruin calculation. All n rounds are completed regardless of the intermediate balance. Reaching a loss during play and ending with that loss are different events. A zero threshold includes a break-even ending.

What this excludes

No changing stakes, bankroll constraints, la partage, en prison, multiplier payouts or side bets are included. The wheel is assumed fair and rounds independent. An actual table requires its own rules. A run of past colours does not change this model's next-round probability.

Sources & scope

Sources checked 30 September 2026. Published features and rules may change. Check the exact service, table and jurisdiction before relying on a detail.

  1. Gambling Commission: theoretical and actual RTP
  2. SciPy: binomial distribution and probability functions

Worked example

Consider one £2 colour bet on a single-zero wheel. There are only two net results in this model: +£2 with probability 18/37, and -£2 with probability 19/37. The mean is -£2/37, roughly -5.4p. You cannot actually finish that one bet down 5.4p: the mean summarises the two possible outcomes.

For more spins, the distribution includes more possible endings. The 5th and 95th percentiles describe its spread. They are not loss limits or promises. Read the roulette rules guide if you need to check which bets the model describes.

Calculator questions

What is the chance of winning one red or black bet?

In this model it is 18/37 on a single-zero wheel, about 48.65%, or 18/38 on a double-zero wheel, about 47.37%. Zero and double zero are losing outcomes for the modelled colour bet.

Does a run of red make black more likely?

No. The model assumes independent spins on a fair wheel. Earlier results do not change the probability assigned to the next spin.

Does the calculator stop when my loss limit is reached?

No. Every selected round is completed. The threshold measures the chance of ending at or below a chosen loss, not the chance of hitting a stop-loss during the session.

Does it cover Lightning Roulette, la partage or betting systems?

No. It models fixed-stake red/black bets at 1:1 with all zeros losing. It excludes changing stakes, limited bankrolls, partial refunds and multiplier payouts.