Probability Calculator
Calculate the probability of an event and its odds from favorable and total outcomes.
Probability Calculator
Calculate the probability of an event and its odds from favorable and total outcomes.
Real-World Examples
Probability of rolling a 4 on a 6-sided die (1 favorable, 6 total).
16.67%
Probability of drawing a heart from 52 cards (13 favorable, 52 total).
25%
A bag has 3 red and 7 blue marbles. Probability of red?
30%
Common Mistakes to Avoid
Confusing probability with odds
Fix: Probability is favorable ÷ total, while odds compare favorable to unfavorable outcomes. 25% probability equals 1:3 odds, not 1:4.
Counting total outcomes incorrectly
Fix: The total must include all possible outcomes, not just the favorable ones. For a die, total is 6 even if you only want one face.
Adding probabilities of non-mutually-exclusive events
Fix: If events can happen at the same time, you must subtract their overlap. P(A or B) = P(A) + P(B) − P(A and B).