About this calculator
The second mode combines two independent events: both happening, at least one, exactly one or neither.
How to use it
- Choose one event or two events.
- Enter the outcomes or probabilities.
- Read the probability, odds and complement.
The formula
P(E) = favourable ÷ total; P(A and B) = P(A) × P(B); P(A or B) = P(A) + P(B) − P(A and B)
- P(E)
- probability of event E
Worked example
Drawing an ace from a deck of 52 cards
- There are 4 aces, so P = 4/52 = 1/13 ≈ 0.0769.
- The odds in favour are 1 : 12.
What the result means
Probability and odds are different: a probability of 1/4 means odds of 1 : 3.
Assumptions
- All outcomes are equally likely in the single-event mode.
- Events are independent in the two-event mode.
Limitations
- For dependent events, use the conditional probability calculator.
Frequently asked questions
What is the probability of getting a head?
1/2, since a coin has two equally likely outcomes.
What are odds?
The ratio of favourable to unfavourable outcomes.
Can probability be more than 1?
No. It is always between 0 and 1, or 0% and 100%.
Last reviewed on 6 October 2026. Found a mistake? Tell us.