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Number Needed to Treat (NNT) from Absolute Risk Reduction Calculator

NNT = 1 / ARR.

Compute the number needed to treat from the absolute risk reduction (ARR = control event rate − treatment event rate). NNT = 1 / ARR, rounded up. NNT is the number of patients you must treat for one to benefit. NNT < 10 is usually a clinically strong therapy. Also reports relative risk reduction RRR = ARR / CER.

Daniel Oh By Daniel Oh
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

NNT = 1 / (CER − EER).

In depth

Compute the number needed to treat from the absolute risk reduction (ARR = control event rate − treatment event rate). NNT = 1 / ARR, rounded up. NNT is the number of patients you must treat for one to benefit. NNT < 10 is usually a clinically strong therapy. Also reports relative risk reduction RRR = ARR / CER.