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Probability calculator

Compute the probability of an event from favorable and total outcomes.

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The Probability calculator turns Favorable outcomes, Total outcomes into Probability, Probability (%), instantly and for free. For instance, with Favorable outcomes = 1 and Total outcomes = 6 it returns Probability = 0.167 and Probability (%) = 16.67%.

How to use it

  1. Enter your values: Favorable outcomes, Total outcomes.
  2. Read the result instantly: Probability, Probability (%).

Frequently asked questions

How does the Probability calculator work?

It takes Favorable outcomes and Total outcomes and derives Probability and Probability (%) from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

2 values: Favorable outcomes and Total outcomes. Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Favorable outcomes = 1 and Total outcomes = 6, the calculator returns Probability = 0.167 and Probability (%) = 16.67%. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What does it give for smaller values?

Scaled down to Favorable outcomes = 1 and Total outcomes = 3, Probability comes out at 0.333. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Summarising a dataset before drawing conclusions from it, checking whether a difference between two groups is real, and putting an interval around an estimate.

What is the most common mistake?

Reading a p-value as the probability that the hypothesis is wrong. It is the probability of seeing data at least this extreme if the null were true — a different statement, and a much weaker one.

What is the difference between the Probability calculator and the Odds to probability converter?

This one returns Probability and Probability (%); the Odds to probability converter returns Implied probability and Decimal odds. That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Binomial Probability Calculator is the closest one after this: Get P(X=k) and every cumulative form at once for up to 1000 trials, with the mean, variance, mode and a chart of the whole distribution.

What else is worth having open alongside it?

Dice Roll Probability Calculator and Loot drop probability calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from, and how current are they?

Distributions and test statistics are computed from their standard definitions, not from a lookup table, so results carry more digits than a printed table would. The assumptions each test makes are stated with it.

Further reading

All guides →
ExplainerProbability Basics, With ExamplesProbability measures how likely something is, from 0 to 1. Here's the basic idea, how to combine events with AND and OR, and the complement.ExplainerA 1 % Drop Rate Does Not Mean One Hundred RunsAt 1 %, a hundred attempts give you 63.4 % — not certainty. Ninety per cent takes 230 attempts and ninety-nine takes 459, and more than a third of players are still empty-handed at a hundred.ExplainerMean, Median and Mode: What's the Difference?Mean, median and mode all describe the 'middle' of your data — but answer different questions. Here's what each means, with examples and when to use which.How-toHow to Calculate Standard Deviation (Step by Step)Standard deviation measures how spread out your data is. Here's the formula, a worked example, and the difference between population and sample.How-toPercentage Change: Increase and DecreaseSubtract old from new, divide by the old value, times 100. Here's the formula, why increases and decreases aren't symmetric, and where it's used.How-toLCM and GCD ExplainedThe GCD is the biggest shared divisor; the LCM is the smallest shared multiple. Here's what each means, how to find them with prime factors, and the shortcut linking them.