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Probability calculator

Compute single-event odds, the chance of at least one success in repeated trials, and full binomial probabilities.

Probability

Probability of rolling a 6 on one die.

Result

Result appears here.

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Three probability questions

Single event covers the basics: how likely is one outcome out of all possibilities, like drawing an ace from a deck. Repeated trials answers at least once questions, such as the chance of winning at least one raffle with ten tickets.

Binomial mode handles exactly k successes in n independent trials, the classic coin-flip math behind A/B tests, quality control, and game odds.

Reading the answer

Every result shows the percentage, the raw decimal probability, and the friendlier 1 in N odds format. The binomial view also reports how many combinations produce that outcome.

All modes assume independent trials with a constant chance per trial, which fits dice, coins, and draws with replacement.

Probability Calc FAQs

What is the difference between probability and odds?
Probability is successes divided by total outcomes. Odds of 1 in N is just another way to say the same thing; this tool shows both.
When do I use the binomial mode?
When you repeat the same yes/no trial a fixed number of times and want the chance of an exact success count, like 3 heads in 10 flips.
Does it assume each trial is independent?
Yes. The formulas assume the chance stays the same every trial, as with dice or coin flips. Card draws without replacement need different math.
Why is at-least-once not just p times n?
Because trials can overlap. The correct formula is 1 minus the chance of failing every trial, which this tool computes for you.
Can n be very large?
Up to 1000 trials. Beyond that the numbers underflow or the combinations become astronomically large.
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