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Probability Calculator
Probability Nebula
Bayesian Logic & Likelihood Determinism
About the Probability Calculator
Calculate the probability of an event as the number of favourable outcomes divided by the total number of possible outcomes.
How to use the Probability Calculator
- Enter the number of Favorable outcomes for Event A.
- Enter the total number of possible outcomes under Universe (Total Outcomes).
- Press Calculate to see the probability as a fraction, decimal and percentage.
Formula and method
P(A) = favourable outcomes ÷ total outcomes. The probability that A does not happen is 1 − P(A).
Worked example
Drawing an ace from a 52-card deck: 4 ÷ 52 = 1/13 ≈ 7.69%.
Two dice. The chance that two dice add up to 7 is 6 out of 36 outcomes, which is 1/6 (about 16.7%). The chance of at least one head in two coin flips is 1 − (1/2 × 1/2) = 3/4.
When to use the Probability Calculator
- Working out chances in games, cards and dice.
- Solving probability questions for school or exams.
- Estimating the chance of two events happening together or at least once.
Common mistakes to avoid
- Adding probabilities for events that are not mutually exclusive.
- Believing in the gambler's fallacy: past results do not change independent events.
Tips
- Probability is always between 0 (impossible) and 1 (certain).
- For independent events, multiply probabilities: two heads in a row is 0.5 × 0.5 = 0.25.
Frequently Asked Questions
Probability compares favourable outcomes to all outcomes. Odds compare favourable to unfavourable outcomes.
From 0 (impossible) to 1 (certain), or 0% to 100%.
Events where the result of one does not affect the other, such as two separate coin flips.