Number Needed to Treat (NNT) Calculator
Find how many people you need to treat for one to benefit. Enter the event rate in the control group and in the treatment group.
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What NNT tells you
The number needed to treat is how many people must receive a treatment for one additional person to benefit compared with the control condition. A smaller number means a more effective intervention. It is a plain-language way to express a difference in event rates that stakeholders find easier to act on than a percentage.
How it is calculated
First the absolute risk reduction is the control event rate minus the treatment event rate. The number needed to treat is 1 divided by that reduction, rounded up to a whole person. If the treatment increases the event rate instead, the same figure becomes a number needed to harm.
Frequently asked questions
What if the two rates are equal?
When the event rates are identical there is no risk reduction, so the number needed to treat is infinite: no amount of treating produces a difference.
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