Number Needed to Treat Calculator

About this calculator

The number needed to treat (NNT) is a clinical measure of treatment effect, calculated as NNT = 1/ARR, where ARR (absolute risk reduction) is the difference between the event rate in the control group and the event rate in the treatment group from a clinical trial. NNT tells you, on average, how many patients need to receive a treatment for one additional patient to benefit — an NNT of 5 means treating 5 people prevents one bad outcome that would otherwise have occurred.

Physicians and clinicians use NNT alongside relative risk to weigh a treatment's real-world benefit against its cost, side effects, or number needed to harm (NNH) when counseling patients, while epidemiologists and health-policy analysts use it to compare the cost-effectiveness of different drugs or interventions across a population. Medical students and pharmacists also use NNT as a standard evidence-based-medicine metric when interpreting clinical trial results.