Simple Probability Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
The probability of a simple event is calculated with (favorable outcomes ÷ possible outcomes) × 100. For example, the probability of rolling a 6 on a 6-sided die is 1 ÷ 6 × 100, or about 16.67%.
Explanation
This formula applies to situations where every possible outcome has an equal chance of occurring (a fair die, drawing a card from a well-shuffled deck, a ball drawn at random from an urn). The number of "favorable outcomes" counts the results that match the event you're looking for, and the number of "possible outcomes" counts all conceivable results. The result is always between 0% (impossible event) and 100% (certain event). This approach, known as classical or Laplace probability, doesn't directly apply to events with non-equally-likely outcomes (like tomorrow's weather), which require other statistical methods. For a more general percentage calculation, see our percentage calculator.
Example: rolling a 6 on a die
Inputs
Favorable outcomes: 1 (the 6). Possible outcomes: 6 (the faces of the die).
Calculation
Probability = (1 ÷ 6) × 100 ≈ 16.67%.
Result
The probability of rolling a 6 is about 16.67%.
Frequently asked questions
Why is probability always between 0% and 100%?
Because the number of favorable outcomes can never be negative, nor exceed the total number of possible outcomes. A probability of 0% means the event can never happen, and 100% means it's certain to happen.
Does this formula work for two combined events (for example, two dice)?
Not directly for a complex combined calculation: you first need to determine the total number of possible combinations (36 for two 6-sided dice) and the number of combinations favorable to the event you're looking for, then apply the same formula with those two numbers.
What's the difference between probability and statistics?
Probability predicts the chance an event will occur before it happens (e.g., the chance of getting heads on a coin flip). Statistics, on the other hand, analyzes data that has already been observed (e.g., the number of times heads actually came up over 100 past flips). The two fields are related but answer different questions.