Probability Calculator

Calculate single event, compound, conditional, and Bayes theorem probabilities with formula display.

Favorable Outcomes

Total Outcomes

Favorable outcomes must be a non-negative integer less than or equal to total outcomes (total must be > 0).

Result

Enter values above to calculate the probability.

P(A) = favorable outcomes / total outcomes

P(A AND B) = P(A) × P(B) (independent)

P(A OR B) = P(A) + P(B) − P(A AND B)

P(A|B) = P(A∩B) / P(B)

Bayes: P(A|B) = P(B|A) × P(A) / P(B)

1

Choose a probability type

Select Single Event, Compound, Conditional, or Bayes from the tabs.
2

Enter values

Fill in the required fields for your chosen probability type.
3

Read the result

The probability is shown as a fraction, decimal, and percentage.

What is conditional probability?

P(A|B) is the probability of A given that B has occurred. It equals P(A and B) / P(B).

What is Bayes theorem?

Bayes theorem calculates P(A|B) from P(B|A), P(A), and P(B): P(A|B) = P(B|A) x P(A) / P(B).

What is the difference between AND and OR probability?

P(A AND B) = P(A) x P(B) for independent events. P(A OR B) = P(A) + P(B) - P(A AND B).

Is my data sent anywhere?

No. All calculations run in your browser.

Solve probability problems with multiple modes. Calculate single-event

probability from favorable and total outcomes, compound event

probabilities (AND, OR), conditional probability P(A|B), and Bayes

theorem. Each mode shows the formula used and displays results as

fractions, decimals, and percentages. All processing runs in your

browser.

Calculate mean, median, mode, standard deviation, variance, quartiles, and more from a data set. Includes histogram.

Calculate percentages instantly — find X% of Y, what percentage X is of Y, or the percentage change between two values.