Probability Calculator: Single Event, A and B, A or B, Not A
Use “one event” to turn favourable ÷ total outcomes into a probability, fraction, percentage and odds. Use “two events” for independent events A and B.
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P(A)
1/13
- Decimal
- 0.076923
- Percentage
- 7.6923%
- P(not A)
- 12/13
- Odds in favour
- 1 : 12
Show working
- P(A) = favourable / total = 4/52
- = 1/13 = 0.076923 = 7.6923%
- P(A′) = 1 − P(A) = 12/13
How to use
- Choose one event or two independent events.
- Enter the counts, or the two probabilities between 0 and 1.
- Read the probability and the other results.
Good to know
One event: P(A) = favourable outcomes ÷ total equally likely outcomes. Drawing an ace from 52 cards: 4/52 = 1/13 ≈ 7.69%. P(not A) = 1 − P(A).
Two independent events: P(A and B) = P(A) × P(B); P(A or B) = P(A) + P(B) − P(A and B); P(neither) = (1 − P(A))(1 − P(B)). Independence means one does not change the chance of the other, like two coin tosses.
Odds are not the same as probability: odds of 1 : 12 mean 1 favourable outcome for every 12 unfavourable ones, which is a probability of 1/13.
Questions
What is the probability of getting a 6 on a die?
1/6 ≈ 16.67%. One favourable outcome out of six.
How do I find P(A or B)?
Add the two probabilities and subtract the overlap: P(A) + P(B) − P(A and B).
What if the events are not independent?
Then P(A and B) = P(A) × P(B given A). This calculator assumes independence in two-event mode.
Can a probability be more than 1?
No. It is always between 0 (impossible) and 1 (certain).
Is my data stored or sent anywhere?
No. The calculation runs entirely in your browser; nothing you type leaves your device.