Incidence Rate Calculator

Work out incidence rate instantly with clear inputs, formula shown and shareable results.

About Incidence Rate Calculator

Divides new cases by the person-time at risk to give a true incidence rate, then scales it to the chosen population multiplier.

Formula

Incidence rate

Incidence rate = new cases / person-time at risk, expressed per 1,000, 10,000 or 100,000 person-years

Worked example

With the default values below, Incidence Rate Calculator returns Incidence rate of 24.000. Change any input above and every figure here is recalculated in your browser.

Inputs used

New cases observedaccepts 0–1,000,000: 120
Person-time at riskaccepts 0.1–100,000,000 person-years: 5,000 person-years
Express perone of Per 1,000 person-years, Per 10,000, Per 100,000: Per 1,000 person-years

Results

Incidence rate: 24.000
Rate per person-year: 0.024000
Rate per 100,000 person-years: 2,400.00
Person-time denominator: 5,000.0

Step by step

1Values used
2Incidence rate
3Incidence rate= 24.000
4Rate per person-year= 0.024000
5Rate per 100,000 person-years= 2,400.00
6Person-time denominator= 5,000.0

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 6 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 does this differ from cumulative incidence?

Cumulative incidence divides cases by the number of people at the start; an incidence rate uses person-time and handles varying follow-up.

Who contributes person-time?

Only people still at risk. Time after diagnosis, death or loss to follow-up is excluded.