Number Needed to Treat (NNT) Calculator
Calculate the impact of a medical intervention by determining how many patients need to be treated to prevent one additional adverse outcome.
Event Rates
Enter the number of events and total patients for each group.
Control Group
Experimental Group
Definitions
- NNT (Number Needed to Treat)
- Number of patients you need to treat to prevent one additional bad outcome.
- ARR (Absolute Risk Reduction)
- The absolute difference in event rates between control and experimental groups.
- RRR (Relative Risk Reduction)
- The proportion of risk reduced by the intervention.
Results
Calculated risk metrics and NNT
Enter event data to view NNT statistics.
About NNT and Risk Reduction
The Number Needed to Treat (NNT) is an epidemiological measure used to communicate the effectiveness of a health-care intervention. It is defined as the number of patients who need to be treated for one of them to benefit compared with a control in a clinical trial.
Formulas
Control Event Rate (CER) = Control Events / Control Total
Experimental Event Rate (EER) = Experimental Events / Experimental Total
Absolute Risk Reduction (ARR) = | CER - EER |
Number Needed to Treat (NNT) = 1 / ARR
Note: NNT is always rounded up to the nearest whole number.
Interpretation
- NNT = 1: Every patient treated benefits (ideal).
- Lower NNT: More effective intervention.
- Higher NNT: Less effective intervention.
Number Needed to Harm (NNH)
If the Experimental Event Rate is higher than the Control Event Rate (e.g., side effects or adverse outcomes are more common in the treatment group), the calculation yields the Number Needed to Harm (NNH). This indicates how many patients need to be exposed to the risk factor to cause one additional person to be harmed.
Disclaimer: This tool is intended for educational and reference purposes only. It should not be used as a substitute for professional medical judgment or advice.