Math & science
Probability Calculator
Calculate basic probability or conditional probability with decimal, percentage, and complement outputs.
Interactive calculator
Solve simple and conditional probability
Switch between basic probability and conditional probability to calculate decimal odds, percentage chance, and complement.
Results
Probability
0.3
Percent chance
30%
Complement
0.7
How to use it
- 01Choose whether you are solving a basic probability or a conditional probability problem.
- 02Enter the two event counts required for that mode.
- 03Review the probability as a decimal, percentage, and complement.
Result guide
- The event count in the numerator cannot be larger than the total or given-event count.
- Complement shows the probability that the selected event does not occur.
- This launch version covers direct event-count probability rather than full distributions.
About this calculator
Probability pages are useful because users often need a clean conversion from event counts into decimal odds and percentage chance.
A single page that handles both simple and conditional probability is more practical than separating closely related event-probability questions into several tiny tools.
Frequently asked questions
What is the difference between simple and conditional probability?
Simple probability uses all possible outcomes as the denominator, while conditional probability limits the denominator to the outcomes where another event is already known to have happened.
Why show complement too?
Because many questions ask for the chance of an event not happening, and the complement gives that immediately.
Can the event count exceed the total count?
No. If it does, the setup is invalid and the calculator returns no result.
Method and limitations
This calculator uses the formula and assumptions described on this page. We do not claim independent professional review. Direct references will be listed here when they support a specific rule or data source used by this calculator.
Results are estimates for general information. Verify current rules and assumptions before making financial, tax, or health decisions.
Read our Editorial and Verification Policy →Related calculators
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