Probability Calculator
Calculate probability of events
Calculator
How to Use
Calculate probability and odds
Select scenario
Choose single event, combined, or conditional
Enter events
Input favorable and total outcomes
View probability
See probability as fraction and percent
Convert to odds
See equivalent odds representation
Probability Formulas
P(Event) = Favorable / Total P(A and B) = P(A) × P(B) [independent] P(A or B) = P(A) + P(B) - P(A and B)
Probability ranges from 0 (impossible) to 1 (certain). Convert to percentage by multiplying by 100.
Frequently Asked Questions
Probability = Favorable outcomes / Total outcomes. Rolling a 6 on a die: 1 favorable, 6 total = 1/6 ≈ 16.7%. Drawing a heart from a deck: 13 hearts / 52 cards = 25%.
For independent events, multiply probabilities. Probability of two heads in a row: 0.5 × 0.5 = 0.25 (25%). For dependent events, use conditional probability: P(A and B) = P(A) × P(B|A).
Add probabilities, subtract overlap. P(A or B) = P(A) + P(B) - P(A and B). Rolling 1 or even: P(1)=1/6, P(even)=3/6, no overlap, so 1/6 + 3/6 = 4/6 = 66.7%.
Probability is favorable/total (1/6 for rolling a 6). Odds are favorable:unfavorable (1:5 for rolling a 6). Convert: Odds a:b → Probability = a/(a+b). 1:5 → 1/(1+5) = 1/6.