Number Needed to Harm (NNH) Calculator / Clinical Epidemiology Calculation

NNH Calculator | Number Needed to Harm Tool (0-100% Input)

⚠️ Number Needed to Harm (NNH)

Calculate how many patients need to be exposed to a treatment to cause one additional adverse event.
Enter values as percentages (0% to 100%). NNH = 1 / Absolute Risk Increase (ARI).

CER %
Adverse event rate in control group (0% to 100%)
EER %
Adverse event rate in treatment group (0% to 100%)
πŸ’‘ NNH = 1 / ((EER% – CER%) / 100) when EER > CER. Lower NNH indicates greater harm risk.
πŸ“‹ Calculation & Results
Number Needed to Harm (NNH)
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πŸ“ Step‑by‑step derivation
Parameter / StepFormulaCalculation with values
Click "Calculate" to see detailed steps
βš•οΈ NNH interpretation: Lower NNH indicates higher risk of harm. NNH = ∞ when no harm difference.
Formula: ARI = (EER% – CER%) / 100, then NNH = 1 / ARI (when EER > CER).

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What is Number Needed to Harm (NNH)

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