NNT Calculator
Calculate the Number Needed to Treat (NNT) from a study’s control and treatment event rates, along with the risk reduction it represents.
What is NNT
Number Needed to Treat (NNT) is a common way researchers and clinicians communicate how effective a treatment is in practical terms: it’s the number of people who would need to receive the treatment for one additional person to benefit (or avoid a bad outcome), compared with the control group.
How it’s calculated
NNT is the reciprocal of the Absolute Risk Reduction (ARR), where ARR is the control group’s event rate minus the treatment group’s event rate. This calculator also reports the Relative Risk Reduction (ARR divided by the control rate). If the treatment group actually has a higher event rate than the control group, the calculator instead reports the Number Needed to Harm (NNH), using the same logic in reverse.
Note: NNT is only as reliable as the study it comes from, and results are typically reported with a specific time frame and population in mind. This calculator is a general reference and educational tool, not a substitute for reading the full source study or professional clinical judgment.