Probability Calculator
Calculate probability of events.
Runs locally in your browser
Your inputs are processed locally in your browser and are not uploaded or stored by us.
Calculate the simple probability of an event occurring based on favorable and equally likely total outcomes.
How to calculate simple probability
- Enter the number of favorable outcomes.
- Enter the total number of equally likely outcomes.
- Click "Calculate" to see the probability, percentage, and complement.
Probability Formula
P(event) = favorable outcomes / total equally likely outcomes
This calculator divides the favorable outcomes by the total outcomes to find the probability. It then multiplies by 100 to determine the percentage. The complement (the probability of the event not happening) is calculated as 1 − probability.
Rolling a fair six-sided die
Favorable outcomes (rolling a specific number)1
Total equally likely outcomes6
P(event) = 1 / 6 ≈ 0.166666...
Percentage ≈ 16.666...
Complement = 5 / 6 ≈ 83.333...
Result: Probability: 0.166667 (16.67%)
Notes
- Favorable outcomes must be a non-negative integer. Total outcomes must be a positive integer.
- Favorable outcomes cannot exceed total outcomes (e.g., 10 / 10 produces 100%, and 0 / 10 produces 0%).
- This version assumes every outcome in the total count is equally likely.
- This calculator does not model conditional probability, dependent events, Bayes’ theorem, or probability distributions.
- Calculations use JavaScript floating-point numbers, so some decimal results (like 1/6) may be approximate.
- Your calculator inputs are processed locally in your browser and are not uploaded or stored by us.