This learning resource is linked to the ARR and NNT / NNH Calculator.
Use the ARR and NNT / NNH Calculator
What This Calculator Does
Use comparable adverse-event risks over the same follow-up period. NNT/NNH is rounded up; no confidence intervals or treatment recommendation.
Information Required
| Input | Field Type | Unit |
|---|---|---|
| Control adverse-event risk (%) | Number | As specified |
| Treatment adverse-event risk (%) | Number | As specified |
| Shared follow-up period (e.g. 12 months) | Text | As specified |
Step-by-Step Instructions
- Open the calculator using the button below.
- Collect the required source data and confirm that it is current and approved for use.
- Enter each value in the corresponding field.
- Use consistent units and perform conversions before calculation.
- Run the calculation and review the displayed output.
- Check the result for reasonableness and compare it with the relevant requirement.
- Document or independently verify the result when it supports GMP activity.
Formula Reference
ARR = control adverse-event risk − treatment risk; NNT = 1/ARR (fraction); NNH = 1/abs(ARR) when ARR < 0
Example
Input: control=20, treatment=10, followup=12 months
Output: ARR=10 percentage points; NNT=10 over 12 months
Good Practice
Use the calculator as a controlled aid, not as a replacement for an approved procedure, validated spreadsheet, qualified software, or professional judgement where those controls are required.