Fisher exact test calculator
Enter the four counts of a 2 by 2 table. The calculator keeps margins fixed and sums probabilities of the relevant tables.
Tables with the same margins
| a | b | c | d | Probability |
|---|---|---|---|---|
| Fill in the fields above — the result is computed on this page. | ||||
How do I use this page?
- Enter four non-negative counts.
- Choose the alternative direction.
- Read the exact p-value and odds ratio.
What this page does not do: With zero cells the raw odds ratio may be infinite or undefined. This calculator does not compute an odds-ratio confidence interval.
Further reading
Theory — what is Fisher's exact test?
Fisher's exact test checks whether two binary variables are related within a 2 by 2 table. The probability of each possible arrangement of counts comes from the hypergeometric distribution, with row and column sums fixed at the observed values. The two-sided p-value is the sum of probabilities of tables as extreme or more extreme than the one observed. The test is especially useful with small expected counts, where the chi-square test can be unreliable.
Frequently asked questions
When should I use Fisher rather than chi-square?
Is the result exact?
See also
A/B test calculator
Compare two proportions in an A/B test. Calculate conversion rates, difference, uplift, z score, p value and c
A/B test planning — sample size, MDE and duration
Plan a two-proportion experiment, estimate detectable effect and traffic duration.
ACF and PACF autocorrelation calculator
Calculate ACF and PACF across time-series lags. Review the chart, reference bounds and coefficient table.