Calculating Probability: Formula, Odds, and Examples
Learn how to calculate probability with simple formulas, common examples, and the difference between probability and odds.
Searching calculating probability usually means you want to know the chance that an event will happen.
Probability Formula
Probability = Favorable outcomes / Total possible outcomes
The result can be written as a fraction, decimal, or percentage.
Example
What is the probability of rolling a 3 on a fair six-sided die?
- Favorable outcomes: 1
- Total outcomes: 6
Probability = 1 / 6 = 0.1667, or 16.67%
Probability vs Odds
Probability measures chance out of all possible outcomes. Odds compare favorable outcomes to unfavorable outcomes.
For the die example:
- Probability of rolling a 3 = 1/6
- Odds in favor = 1:5
More Examples
Drawing one ace from a standard 52-card deck:
4 / 52 = 1 / 13 = 7.69%
Flipping heads on a fair coin:
1 / 2 = 50%
The Bottom Line
To calculate probability, divide favorable outcomes by total outcomes. If you want to compare betting-style outcomes, our Odds Calculator can help.
How to Calculate: Step-by-Step Guide
Count favorable outcomes
Find the number of results you want.
Count total outcomes
Determine all possible equally likely results.
Divide favorable by total
That ratio gives the probability.