💊 Number Needed to Treat Calculator
Calculate absolute risk reduction, relative risk reduction, and number needed to treat or harm.
📊 Statistics📐 Formula included🧠 Practice questions✓ Free
Please enter valid values.
Formula and Explanation
Calculate absolute risk reduction, relative risk reduction, and number needed to treat or harm.
| Concept | Formula or rule |
|---|---|
| Number Needed to Treat Calculator | NNT = 1 / |CER − EER| |
How to Use This Calculator
- Enter the sample, counts, probabilities, or summary statistics requested above.
- Keep paired lists in the same order and separate values with commas.
- Select the correct test direction or sample/population option when available.
- Press Calculate and interpret the result together with the supporting statistics.
Worked Example
Example: Control risk 20% and treatment risk 12% gives ARR=8%.
✓ NNT = 1/0.08 = 12.5, conventionally rounded up to 13
Where This Is Used
School & coursework
Check homework, understand formulas, and verify step-by-step statistics exercises.
Research
Explore estimates, uncertainty, distributions, and relationships before using full statistical software.
Business & data analysis
Summarize variation, compare groups, and communicate data-driven findings clearly.
Common Mistakes to Avoid
⚠️
Rounding down
NNT is usually rounded up to the next whole person.
NNT is usually rounded up to the next whole person.
⚠️
Ignoring time horizon
Risks must refer to the same follow-up period.
Risks must refer to the same follow-up period.
⚠️
Using NNT without uncertainty
Confidence intervals may be wide or cross no effect.
Confidence intervals may be wide or cross no effect.
Practice Questions
1. CER=10%, EER=5%. Find NNT.
Answer: 20
2. CER=20%, EER=20%. Is NNT finite?
Answer: No; there is no absolute effect.
3. Should NNT be rounded up or down?
Answer: Up.
Frequently Asked Questions
What is a better NNT?▾
A smaller positive NNT indicates a larger absolute benefit, but context and harms matter.
What if treatment risk is higher?▾
The result is number needed to harm (NNH).
Why can NNT differ across populations?▾
Baseline risk changes absolute benefit.