Probability Calculator

Calculate the probability of events, including single events, multiple events, c...

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Probability Calculator Features

Calculate any probability

5 calculation types
Combinations (nCr)
Permutations (nPr)
Binomial probability
AND/OR/NOT logic
Formula display
No signup required
Free unlimited use
Mobile-friendly
100% private
Instant results
Educational tool

Why Use Probability Calculator?

All Probability Types

Calculate single event, multiple event, combinations, permutations, and binomial probability all in one tool.

Common Scenarios

Built-in support for coin flips, dice rolls, card draws, and custom probability scenarios with easy inputs.

Multiple Formats

Results displayed as fraction, decimal, and percentage. Choose the format that works best for your needs.

Formula Reference

See the formulas used and understand how probability calculations work. Learn while you calculate.

Common Use Cases

Probability for every scenario

Statistics & Math Class

Check homework problems and understand probability concepts. Great for learning combinations, permutations, and probability theory.

Games & Gambling

Calculate odds for board games, card games, dice games, and other games of chance. Understand your true chances of winning.

Scientific Research

Calculate statistical probabilities for experiments and research. Determine likelihood of outcomes in controlled trials.

Risk Assessment

Evaluate probability of multiple events occurring for business decisions, insurance calculations, or project planning.

How It Works

1

Select Calculation Type

Choose what type of probability you want to calculate - single event, multiple events, combinations, permutations, or binomial.

2

Enter Your Values

Input the relevant numbers - favorable outcomes, total outcomes, or individual event probabilities depending on calculation type.

3

For Multiple Events

Choose AND (both happen), OR (either happens), or NOT (complement) to combine event probabilities.

4

Get Results

See probability as fraction, decimal, and percentage. Review the formula used to understand the calculation.

Pro Tips for Probability

Remember the Basics

Probability always ranges from 0 (impossible) to 1 (certain). If your result is outside this range, double-check your inputs.

Independent vs Dependent

Use simple multiplication only for independent events. For dependent events (like drawing cards without replacement), calculations are more complex.

The Complement Trick

Sometimes it's easier to calculate P(not A) and subtract from 1. Example: P(at least one head in 3 flips) = 1 - P(no heads) = 1 - 0.125 = 0.875.

Check with Fractions

When possible, verify your answer makes sense. The probability of rolling a 6 should be 1/6, not 1/36. Context helps catch errors.

Frequently Asked Questions

For a fair coin, the probability of heads is 1/2 = 0.5 = 50%. Enter 1 favorable outcome (heads) and 2 total outcomes (heads or tails).
For a fair die, P(6) = 1/6 ≈ 0.167 ≈ 16.67%. There's 1 favorable outcome (rolling 6) out of 6 total possible outcomes.
For independent events A AND B, multiply the probabilities: P(A and B) = P(A) × P(B). For example, flipping heads twice: 0.5 × 0.5 = 0.25 = 25%.
For mutually exclusive events: P(A or B) = P(A) + P(B). For non-exclusive: P(A or B) = P(A) + P(B) - P(A and B).
Combinations (nCr) don't care about order - selecting 3 items from 10. Permutations (nPr) care about order - arranging 3 items from 10 in sequence.
Binomial probability calculates the chance of exactly k successes in n trials, each with probability p. Example: probability of getting exactly 3 heads in 5 coin flips.
For drawing a specific card from a 52-card deck: 1/52 ≈ 1.92%. For drawing any ace: 4/52 = 1/13 ≈ 7.69% (4 aces out of 52 cards).
The complement is the probability of an event NOT happening. P(not A) = 1 - P(A). If P(rain) = 30%, then P(no rain) = 70%.
Yes! Enter '50%' or '0.5' or '1/2' - the calculator accepts all formats and converts between them.
Yes. All calculations happen in your browser. Nothing is uploaded to any server.

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