Find the chance of an event when every basic outcome in the sample space is equally likely.
A fair die has 3 even results among 6 possible results, so P(even) = 3/6 = 1/2 = 50%.
3 favorable outcomes out of 6 equally likely outcomes.
How to Use the Probability Calculator
Count the outcomes that satisfy your event and the outcomes in the full sample space. Enter those counts, then calculate. The favorable count cannot exceed the total. The calculator shows the probability as a reduced fraction, decimal, and percentage, plus its complement and odds in favor.
Probability From Equally Likely Outcomes
For a finite sample space whose individual outcomes are equally likely, divide the favorable count by the total count. An impossible event has probability 0; a certain event has probability 1. When outcomes have different weights, this count-only formula does not apply.
Worked Example: Even Number on a Fair Die
The sample space is {1, 2, 3, 4, 5, 6}. The favorable outcomes are {2, 4, 6}, so P(even) = 3/6 = 1/2 = 0.5 = 50%. The complementary event is an odd result, also 50%.
How Probability Differs From Odds
Probability compares favorable outcomes with all outcomes. Odds in favor compare favorable with unfavorable outcomes. For 3 favorable and 6 total, the unfavorable count is 3, so odds in favor are 3:3, or 1:1. An impossible event has 0:1 odds; a certain event has 1:0 odds.
When Not to Use the Count Formula
Do not use favorable/total counts without checking that the basic outcomes are equally likely. A spinner with unequal sectors, a loaded die, and events assembled from differently weighted outcomes require their actual probabilities. The calculator does not model dependent draws or conditional probability.
Probability Calculator FAQs
What does a probability of 0.5 mean?
The event has a 50% chance under the stated model.
Can favorable outcomes exceed total outcomes?
No. The favorable event is a subset of the sample space.
Are probability and odds the same?
No. Probability compares favorable to total; odds compare favorable to unfavorable.
Editorial review
SolverCalc names Prof. Dr. Khalil Mudassar as its educational reviewer. The formulas and examples on this page follow the references below.
Sources
Disclaimer
For educational use. Check your class or textbook convention when the problem defines a different range, sequence index, or notation.