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Probability Calculator

Enter the number of favorable outcomes and total equally likely outcomes to compute event probability and related measures.

Number of outcomes where the event occurs.

Total number of equally likely outcomes.

Probability

16.67%

P = favorable / total

Odds

0.200 : 1

Odds in favor

Complement

83.33%

Probability event does not occur

For every 6 equally likely outcomes, the event is expected to occur 1 time(s) on average.

How to Use This Calculator

  1. Specify how many outcomes satisfy the event of interest.
  2. Enter the total number of equally likely outcomes.
  3. Read the probability (percentage), odds, and complement.
  4. Apply these results to games of chance, statistics exercises, or risk assessments.

Formula

Probability = Favorable / Total

Odds = Probability / (1 − Probability)

Complement = 1 − Probability

These formulas assume each outcome is equally likely. For weighted scenarios, multiply probability by outcome weights instead of simple counts.

Full Description

Probability quantifies the chance an event occurs, while odds express the ratio of success to failure. This calculator provides both perspectives along with the complement, illuminating event likelihood from multiple angles. It is useful for classroom problems, tabletop games, or risk communication.

For compound events, break the scenario into favorable and total outcomes using combinatorics or tree diagrams, then enter the counts here.

Frequently Asked Questions

What if outcomes are not equally likely?

Replace counts with weighted counts or compute probability directly from weights (sum of weights for favorable outcomes divided by total weight).

Why do odds differ from probability?

Probability reflects success over all outcomes; odds compare success to failure. Both describe the same event but suit different contexts (e.g., betting uses odds).

Can probability exceed 1?

No. If favorable outcomes exceed total outcomes, adjust your counts; otherwise, the scenario is inconsistent.

How do I handle multiple events?

For independent events, multiply probabilities. For dependent events, apply conditional probability rules before entering counts.