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Relative Risk Reduction Calculator

Calculate relative risk reduction from control and treatment event rates.

About Relative Risk Reduction Calculator

Relative risk reduction is independent of baseline risk, so a 30 per cent reduction sounds identical whether the baseline is 20 per cent or 0.2 per cent. Absolute risk reduction and number needed to treat expose the difference. Reporting only relative reduction is the most common way trial results are made to sound more impressive than they are.

Formula

Relative Risk Reduction

RRR = (control rate − treatment rate) ÷ control rate; NNT = 100 ÷ absolute risk reduction

RRR
Proportional reduction, which sounds impressive regardless of baseline risk
ARR
Percentage-point reduction, which reflects real-world benefit

Worked example

With the default values below, Relative Risk Reduction Calculator returns Relative Risk Reduction of 30.000%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Event rate in the control groupaccepts 0–100 %
20 %
Event rate in the treatment groupaccepts 0–100 %
14 %
Patients per groupminimum 1
500

Results

Relative Risk Reduction
30.000%
Absolute Risk Reduction
6.000%
Number Needed to Treat
16.7
Risk Ratio
0.70000
Events Prevented per Group
30.0

Step by step

  1. 1Values used
  2. 2Relative Risk Reduction
  3. 3Relative Risk Reduction= 30.000
  4. 4Absolute Risk Reduction= 6.000
  5. 5Number Needed to Treat= 16.7
  6. 6Risk Ratio= 0.70000
  7. 7Events Prevented per Group= 30.0

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Relative Risk Reduction calculated?

RRR = (control rate − treatment rate) ÷ control rate; NNT = 100 ÷ absolute risk reduction Relative risk reduction is independent of baseline risk, so a 30 per cent reduction sounds identical whether the baseline is 20 per cent or 0.2 per cent. Absolute risk reduction and number needed to treat expose the difference.

Why does Relative Risk Reduction matter?

Reporting only relative reduction is the most common way trial results are made to sound more impressive than they are.

What values do I need to enter?

This calculator takes 3 inputs: Event rate in the control group, Event rate in the treatment group, Patients per group. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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