Epidemic Growth Rate Calculator

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

About Epidemic Growth Rate Calculator

Estimates the exponential growth rate from two case counts and converts it into a reproduction number using the mean serial interval.

Formula

Growth rate to Rt

r = ln(later cases / earlier cases) / days; Rt = 1 + r x mean serial interval (linear approximation)

Worked example

With the default values below, Epidemic Growth Rate Calculator returns Exponential growth rate of 0.09319. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cases in the earlier periodaccepts 1–100,000,000: 250
Cases in the later periodaccepts 1–100,000,000: 480
Days between the periodsaccepts 0.5–180: 7
Mean serial intervalaccepts 0.5–40 days: 5 days

Results

Exponential growth rate: 0.09319 per day
Growth per day: 9.767%
Reproduction number estimate: 1.466
Growth per week: 92.00%

Step by step

1Values used
2Growth rate to Rt
3Exponential growth rate= 0.09319 per day
4Growth per day= 9.767
5Reproduction number estimate= 1.466
6Growth per week= 92.00

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 or fees or charges 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

Is the linear approximation accurate?

It is good for slow growth; for fast growth the moment-generating function of the serial interval distribution should be used.

Can the growth rate be negative?

Yes. A negative rate means cases are declining and implies an Rt below 1.