Probability Calculator
Calculate the combined probability of two independent events: both, either, neither, and one but not the other, from each event probability.
Calculator by Toolsloft ↗- Both (A and B)
- 0.25
- Either (A or B)
- 0.75
- Neither
- 0.25
- A but not B
- 0.25
- Not A
- 0.5
- Not B
- 0.5
Work out the combined probability of two independent events. Enter the probability of event A and event B, each from 0 to 1, and the tool returns the chance of both happening, either happening, neither happening, and one happening without the other. Handy for coin flips, dice, and simple risk estimates.
How this is calculated
The tool treats A and B as independent events. The probability of both (A and B) is the product of the two, and the probability of either (A or B) is P(A) plus P(B) minus P(A and B). Neither is the product of the complements, following the standard rules of probability for independent events.
How to use
- Enter the probability of event A as a value from 0 to 1.
- Enter the probability of event B the same way.
- Read the chance of both, either, neither, and one without the other.
Examples
- Two coin flips:
P(A) 0.5 and P(B) 0.5 gives both = 0.25 - Either event:
P(A) 0.3 and P(B) 0.4 gives either = 0.58 - Neither:
P(A) 0.3 and P(B) 0.4 gives neither = 0.42
FAQ
- What does independent mean here?
- Two events are independent when one happening does not change the chance of the other. Coin flips and separate dice rolls are independent, so the probability of both is simply the two probabilities multiplied together.
- How do I enter a probability?
- Enter each probability as a decimal from 0 to 1. A 25 percent chance is 0.25, a coin flip is 0.5, and a certainty is 1.