Probability Calculator
Enter the number of successful outcomes versus the total pool space to calculate probability and exact statistical odds.
Probability of an Event
How many times the event can occur.
The size of the entire pool of possibilities.
Probability of Event P(A)
33.33%
0.333333
Inverse Probability P(A')
66.67%
Chance of NOT occurring
Odds For Event
2 : 4
Successes vs Failures
Understanding Probability and Odds
Probability is the mathematical measurement of how likely an event is to occur out of a defined set of total possibilities. It ranges on a scale from 0 (impossible) to 1 (absolute certainty).
How to Calculate Probability
The fundamental equation for probability, often denoted as P(A), compares the number of favorable outcomes against the total number of all possible outcomes.
- Probability Equation:
P(A) = Expected Outcomes / Total Possible Outcomes - Example: Rolling a die and landing on a "4". The expected outcome is 1 (there is only one "4" on the die) and the total possible outcomes are 6.
P(4) = 1/6 ≈ 16.67%.
Inverse Probability
The inverse probability, also known as the complement P(A'), is the exact likelihood that an event will not happen. Because the sum of all probabilities must equal 100% (or 1), finding the inverse is as simple as subtracting your first probability from 100%. If you have a 25% chance of winning, you have a 75% chance of losing.
Probability vs. Odds
While they are often used interchangeably in casual conversation, "Probability" and "Odds" are mathematically different concepts:
- Probability measures Successes vs Total Pool. (e.g. 1 in 6)
- Odds measures Successes vs Failures explicitly. (e.g. 1 : 5)