Risk Ratio Calculator

Calculate relative risk between an exposed and unexposed group.

About Risk Ratio Calculator

Risk ratio compares probabilities directly and is the most intuitive measure. The odds ratio approximates it only when the outcome is rare, diverging substantially for common outcomes. Reporting an odds ratio as though it were a risk ratio overstates the effect whenever the baseline risk is above about 10 per cent.

Formula

Risk Ratio

RR = risk in exposed ÷ risk in unexposed

risk ratio: Ratio of probabilities, interpretable directly as relative likelihood
odds ratio: Ratio of odds, which exceeds RR when the outcome is common

Worked example

With the default values below, Risk Ratio Calculator returns Risk Ratio of 1.80000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Events in the exposed groupminimum 0: 45
Total in the exposed groupminimum 1: 300
Events in the unexposed groupminimum 0: 25
Total in the unexposed groupminimum 1: 300

Results

Risk Ratio: 1.80000
Risk in the Exposed Group: 15.0000%
Risk in the Unexposed Group: 8.3333%
Odds Ratio for Comparison: 1.94118
Interpretation: Exposure is associated with increased risk

Step by step

1Values used
2Risk Ratio
3Risk Ratio= 1.80000
4Risk in the Exposed Group= 15.0000
5Risk in the Unexposed Group= 8.3333
6Odds Ratio for Comparison= 1.94118
7Interpretation= Exposure is associated with increased risk

Assumptions and limits

The result is derived only from the 4 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 Risk Ratio calculated?

RR = risk in exposed ÷ risk in unexposed Risk ratio compares probabilities directly and is the most intuitive measure. The odds ratio approximates it only when the outcome is rare, diverging substantially for common outcomes.

Why does Risk Ratio matter?

Reporting an odds ratio as though it were a risk ratio overstates the effect whenever the baseline risk is above about 10 per cent.

What values do I need to enter?

This calculator takes 4 inputs: Events in the exposed group, Total in the exposed group, Events in the unexposed group, Total in the unexposed 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.