Statistics
Probability Calculator
Use this probability calculator for basic event chances, complements, odds, and independent repeated trials.
Event probability
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- Complement
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- All trials succeed
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Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the probability calculator solves
Use this probability calculator for basic event chances, complements, odds, and independent repeated trials.
Formula
How to use it
- Enter favorable outcomes.
- Enter total possible outcomes.
- Enter independent trials if needed.
How to read the answer
Probability ranges from 0% to 100%. Complement probability is the chance the event does not happen, and repeated-trial probability assumes each trial starts with the same chance.
Common mistakes and edge cases
- Outcomes must be equally likely for this simple formula.
- Independent trials must not affect each other.
- Favorable outcomes cannot exceed total outcomes.
Worked examples
Simple event
Event probability
30.00%
Coin-style event
Event probability
50.00%
Frequently asked questions
What does independent mean?+
One trial does not change the probability of another trial.
What are odds?+
Odds compare favorable to unfavorable outcomes, while probability compares favorable to total outcomes. For example, 3 favorable and 7 unfavorable outcomes are 3:7 odds and 30% probability.
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Last updated: May 8, 2026