Exact binomial test calculator
Test a success probability without using the normal approximation.
How do I use this page?
- Enter successes and trials.
- Provide p₀ and the pre-specified test direction.
- Read the p-value together with p̂ and both tails.
What this page does not do: Trials must be independent with constant success probability. The test does not measure practical effect size and does not replace a confidence interval.
Further reading
Theory — what is the exact binomial test?
The exact binomial test compares an observed number of successes with a binomial distribution built from an assumed success probability. The one sided version sums the relevant tail of that distribution, while the two sided version adds up every outcome that under the baseline hypothesis is at least as unlikely as the observed one. Because the binomial distribution is discrete, the two sided p value does not need to equal exactly twice the one sided value.
Frequently asked questions
Why is the two-sided p-value not always twice the one-sided value?
Can x be 0 or n?
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.