Probability Calculator

Convert favorable outcomes and total outcomes into a probability, percentage and odds.

Probability Calculator

Convert favorable outcomes and total outcomes into a probability, percentage and odds.

Favorable outcomes

Total possible outcomes

Enter values above and click Calculate — results will appear here with the formula explained.

P(event) = favorable outcomes ÷ total outcomes; P(not event) = 1 − P(event)

How does this work?

Classical probability assumes every outcome is equally likely. Count how many outcomes match your event, divide by how many outcomes exist in total, and the result lies between 0 (impossible) and 1 (certain).

Probabilities of complementary events always sum to exactly 1, so the chance something does not happen is one minus the chance it does. Odds restate the same idea as a ratio of success to failure rather than a fraction of the whole.

AdSense ready — add NEXT_PUBLIC_GOOGLE_ADSENSE_PUBLISHER_ID

728×90 — AdSense

Quick Answer

Probability Calculator computes convert favorable outcomes and total outcomes into a probability, percentage and odds. Formula: P(event) = favorable outcomes ÷ total outcomes. Example: Drawing an ace from a standard 52-card deck has 13 favorable outcomes if we count all spades: P = 13/52 = 1/4 = 25%.

How to Use This Calculator

1Count how many outcomes count as a success for your event.
2Count the total equally likely outcomes.
3Read the probability as a decimal and percentage, plus odds and the complement.

Formula Used

P(event) = favorable outcomes ÷ total outcomes; P(not event) = 1 − P(event)

AdSense ready — add NEXT_PUBLIC_GOOGLE_ADSENSE_PUBLISHER_ID

728×90 — AdSense

Worked Example

Drawing an ace from a standard 52-card deck has 13 favorable outcomes if we count all spades: P = 13/52 = 1/4 = 25%. The complement — not drawing a spade — is 75%, with odds 13:39, which simplifies to 1:3.

AdSense ready — add NEXT_PUBLIC_GOOGLE_ADSENSE_PUBLISHER_ID

728×90 — AdSense

Related Calculators

Random Number Generator

Generate truly even random numbers within any range, with optional uniqueness.

Standard Deviation Calculator

Compute sample and population standard deviation, variance and mean for a data set.

Average Calculator

Calculate the mean and median of any set of numbers, separated by spaces or commas.

Exponent Calculator

Raise any base to any power, including negative and fractional exponents.

Frequently Asked Questions

QWhat is the difference between odds and probability?

Probability divides successes by total outcomes; odds divide successes by failures. A 25% probability corresponds to 1:3 odds.

QDo probabilities of independent events multiply?

Yes. The chance of two heads in two fair coin flips is 1/2 × 1/2 = 1/4, because each flip is unaffected by the last.

QWhen is this formula wrong?

It assumes all outcomes are equally likely. Drawing a card works; 'will it rain tomorrow' needs frequency-based estimates instead of counting.

Quick Answer

Formula Used

P(event) = favorable outcomes ÷ total outcomes; P(not event) = 1 − P(event)

Frequently Asked Questions

QWhat is the difference between odds and probability?

Probability divides successes by total outcomes; odds divide successes by failures. A 25% probability corresponds to 1:3 odds.

QDo probabilities of independent events multiply?

Yes. The chance of two heads in two fair coin flips is 1/2 × 1/2 = 1/4, because each flip is unaffected by the last.

QWhen is this formula wrong?

It assumes all outcomes are equally likely. Drawing a card works; 'will it rain tomorrow' needs frequency-based estimates instead of counting.