Relative Risk Calculator
Relative risk, risk difference, ARR, RRR and NNT with confidence intervals.
Enter your values to see the result.
Relative risk needs a cohort or trial design where you know the number at risk in each group. For case-control data use the odds ratio instead. Results use standard large-sample formulas and are meant to support, not replace, a statistician's review. Check the assumptions behind each method before you report the numbers.
Continue your work
- Odds Ratio Calculator — Use odds ratios for case-control data.
- NNT / NNH Calculator — Get NNT with a confidence interval.
Share this tool
Found it useful? Send it to a friend or teammate.
Rate this tool
0.0
0 ratings
- 5 stars 0
- 4 stars 0
- 3 stars 0
- 2 stars 0
- 1 star 0
Clear instructions
Find steps, examples and limitations below.
Use online
Open the tool in a supported web browser.
Free to use
No sign-up required. Tool-specific limits may apply.
How to use the Relative Risk Calculator
Relative risk, risk difference, ARR, RRR and NNT with confidence intervals.
- 1 Enter the numbers with and without the outcome in the exposed and unexposed groups.
- 2 Choose the confidence level.
- 3 Read the relative risk, risk difference and number needed to treat or harm.
Example and practical tips
30 of 100 exposed people and 15 of 100 unexposed people develop the outcome: relative risk 2.0 (95% CI 1.15 to 3.48) and a risk difference of 15%.
Frequently asked questions
What does a relative risk of 2 mean?
The outcome is twice as likely in the exposed group. A value of 1 means no difference and below 1 means lower risk.
Why report the absolute difference too?
A large relative risk can hide a tiny absolute change when the outcome is rare. The risk difference and NNT show the real-world impact.
Report an issue
Something broken or not quite right? Tell us and we will look into it.