Number needed to treat calculator
Enter events and totals for the treatment and control groups.
Event table
| Group | Event | No event | Total | Risk |
|---|---|---|---|---|
| Fill in the fields above — the result is computed on this page. | ||||
How do I use this page?
- Enter event counts and totals for both groups.
- Inspect the risk-difference sign.
- Read NNT for benefit or NNH for harm.
What this page does not do: The calculator gives point estimates without confidence intervals and does not adjust for group differences. Equal risks imply an infinite NNT and are returned as no finite result. This tool does not replace clinical judgment.
Further reading
Theory — what are NNT and NNH?
NNT, the number needed to treat, is the inverse of the absolute risk reduction. It tells you how many people must receive the intervention to prevent one additional event over a given period. When risk in the intervention group is higher than in the control group, the same calculation describes NNH, the number needed to harm. The figure should be reported alongside a confidence interval rather than as a single rounded number.
Frequently asked questions
Should NNT be rounded?
Why does follow-up time matter?
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.