Serial Interval Estimate Calculator

Work out serial interval estimate instantly with clear inputs, formula shown and shareable results.

About Serial Interval Estimate Calculator

Averages the observed intervals between symptom onset in infector-infectee pairs, the empirical estimate of the serial interval.

Formula

Serial interval

Mean serial interval = sum of onset-to-onset intervals / number of pairs; the standard deviation measures its spread

Worked example

With the default values below, Serial Interval Estimate Calculator returns Mean serial interval of 5.143. Change any input above and every figure here is recalculated in your browser.

Inputs used

Observed serial intervals: 4, 5, 6, 7, 3, 5, 6
Assumed incubation periodaccepts 0.5–30 days: 5 days

Results

Mean serial interval: 5.143 days
Standard deviation: 1.245 days
Transmission pairs observed: 7
Mean minus the assumed incubation period: 0.143 days

Step by step

1Values used
2Serial interval
3Mean serial interval= 5.143 days
4Standard deviation= 1.245 days
5Transmission pairs observed= 7
6Mean minus the assumed incubation period= 0.143 days

Assumptions and limits

The result is derived only from the 2 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 3 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 it differ from the generation interval?

The generation interval measures infection-to-infection times, which are unobservable; the serial interval uses symptom onset as a proxy.

Can a serial interval be negative?

Yes, when pre-symptomatic transmission means the infectee develops symptoms before the infector.