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🦠 Outbreak Spread Simulator Calculator

Enter a starting case count, a basic reproduction number, and a number of generations to see a simplified illustration of exponential case growth.

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cases
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gens
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days

What this calculator does

This is a simplified educational model that shows how case counts can grow generation by generation when each infected case, on average, produces a fixed number of new cases.

How the calculation works

Cases after N generations equal the initial case count multiplied by the reproduction number raised to the power of N: Cases = Initial × R0N. Elapsed time multiplies the number of generations by the average generation interval. Doubling time uses the standard exponential-growth relationship, log(2) ÷ log(R0), scaled by the generation interval.

This is a basic illustrative branching model for general educational use, not a real epidemiological forecasting tool — actual outbreaks are shaped by immunity, interventions, population limits, and many other factors this simple formula ignores.

Last reviewed August 2026