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Basic Reproduction Number Calculator

Work out basic reproduction number instantly with clear inputs, formula shown and shareable results.

About Basic Reproduction Number Calculator

Multiplies transmission probability per contact, contact rate and infectious duration, the classic decomposition of the basic reproduction number.

Formula

R0 decomposition

R0 = transmission probability per contact x contacts per unit time x duration of infectiousness; herd immunity threshold = 1 - 1/R0

Worked example

With the default values below, Basic Reproduction Number Calculator returns Basic reproduction number of 3.600. Change any input above and every figure here is recalculated in your browser.

Inputs used

Transmission probability per contactaccepts 0.001–1
0.05
Contacts per dayaccepts 0.1–200
12
Infectious periodaccepts 0.1–60 days
6 days

Results

Basic reproduction number
3.600
Herd immunity threshold
72.22%
Epidemic potential
Above 1 — sustained transmission expected
Contacts per transmission event
20.0

Step by step

  1. 1Values used
  2. 2R0 decomposition
  3. 3Basic reproduction number= 3.600
  4. 4Herd immunity threshold= 72.22
  5. 5Epidemic potential= Above 1 — sustained transmission expected
  6. 6Contacts per transmission event= 20.0

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 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

Is R0 a property of the pathogen?

No. It depends on contact patterns and behaviour, so the same pathogen has different R0 values in different populations.

What if R0 is below 1?

Each infection produces less than one further infection on average, so transmission chains die out.

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