R0 Reproduction Number Calculator
Enter transmission probability, average contacts per day, and infectious period to instantly compute R0 and see whether an epidemic will spread or die out.
Disease Parameters
R0 = transmission probability × contacts/day × infectious days
Chance a single contact with an infectious person leads to a new infection (0 to 1).
Number of people an infected individual has meaningful contact with each day.
Average number of days an infected person can transmit the disease.
Quick presets
Basic Reproduction Number
Derived Metrics
Herd Immunity Threshold
—
% population immune needed
Generation Time
—
≈ infectious period (days)
Cases after 5 generations
—
starting from 1 case
Sensitivity: R0 vs. Contact Rate
How R0 changes as contacts per day vary (other parameters fixed).
| Contacts/day | R0 | HIT | Verdict |
|---|
Summary
Enter transmission probability, average contacts per day, and infectious period to instantly compute R0 and see whether an epidemic will spread or die out.
How it works
- Enter the per-contact transmission probability (0–1) — the chance that one contact with an infected person leads to a new infection.
- Enter the average number of close contacts per day an infected individual has.
- Enter the infectious period in days — how long a person can transmit the disease.
- The tool computes R0 = transmission probability × contacts per day × infectious days.
- Read the epidemic threshold interpretation: R0 < 1 = declining, R0 = 1 = endemic equilibrium, R0 > 1 = exponential spread.
- The herd immunity threshold (1 − 1/R0) shows the vaccination coverage needed to halt spread.
Use cases
- Model outbreak dynamics during emerging infectious disease events.
- Compare transmissibility across different pathogens or variants.
- Estimate herd immunity thresholds for vaccination planning.
- Teach epidemiology students about the reproduction number concept.
- Evaluate the impact of interventions that reduce contacts or transmission probability.
- Quickly benchmark a pathogen against known R0 values (flu ~1.3, measles ~15).