How the Probability Calculator works.
P(A) = favorable ÷ total; P(not A) = 1−P(A); P(A∩B) = P(A)P(B)Simple mode uses counts; complement and independent modes use probabilities from 0 through 1.
Worked example for the Probability Calculator.
Drawing one red card from 4 red cards among 10 equally likely cards gives probability 0.4, or 40%.
How to read this result.
The result is a model-based proportion or chance under the stated sample-space and independence assumptions, not a promise about one trial.
How the calculation works
Simple probability is favorable outcomes divided by total outcomes; complements are 1−P(A), and independent conjunctions multiply P(A) by P(B). Formula or rule: P(A) = favorable ÷ total; P(not A) = 1−P(A); P(A∩B) = P(A)P(B). Simple mode uses counts; complement and independent modes use probabilities from 0 through 1.
What this calculator does not prove
Probability depends on how outcomes are defined and whether trials are independent and equally likely. The calculator does not estimate a distribution from data or predict certainty. Use the result for the mathematical question shown here; a correct calculation does not by itself establish that the source data, sample, or real-world assumption is appropriate.
Inputs and edge cases to check.
Probabilities must be between 0 and 1, favorable outcomes cannot exceed total outcomes, and a total outcome count must be positive.
What this tool does not include.
Probability depends on how outcomes are defined and whether trials are independent and equally likely. The calculator does not estimate a distribution from data or predict certainty.
Reference guidance and methodology.
Probability Calculator questions.
What does the Probability Calculator calculate?
Calculate simple, complementary, or independent-event probability with explicit sample-space assumptions.
Which formula or algorithm does it use?
P(A) = favorable ÷ total; P(not A) = 1−P(A); P(A∩B) = P(A)P(B). Simple mode uses counts; complement and independent modes use probabilities from 0 through 1.
What limitations or edge cases matter?
Probabilities must be between 0 and 1, favorable outcomes cannot exceed total outcomes, and a total outcome count must be positive. Probability depends on how outcomes are defined and whether trials are independent and equally likely. The calculator does not estimate a distribution from data or predict certainty.