Probability Calculator
Use this probability calculator for common classroom probability questions and quick event comparisons.
It supports a simple favorable-over-total setup as well as two-event modes for independent events and the chance of at least one event occurring.
This makes it useful for math classes, games of chance, and everyday reasoning.
Results are displayed as both probability and complement.
Assumptions
- Basic mode assumes equally likely outcomes.
- Independent-event mode assumes the two events do not affect each other.
- At least one event mode uses the complement rule for two events.
How this calculator works
Formula used
Basic probability uses favorable outcomes divided by total outcomes. Independent events multiply probabilities, while at least one event uses 1 - (1 - P(A))(1 - P(B)).
Example calculation
If the chance of rain is 30% and the chance of traffic delay is 20%, the chance of at least one happening is 44%.
Probability Calculator FAQ
Is this probability calculator exact?
It is designed as a practical estimate or classroom calculator for probability calculator. Results can differ if your teacher, textbook, software, or engineering workflow uses different assumptions, notation, or precision.
Who should use this probability calculator?
Students, parents, teachers, and everyday users can use it for homework checks, class review, exam prep, and quick planning calculations on a desktop or phone.
Does this replace official coursework, lab software, or professional tools?
No. These pages are educational calculators for learning and general use. For graded work, lab reports, engineering decisions, or research, verify the result with your course method or professional software.