Zombie Invasion Calculator

What Is the Zombie Invasion Model?

This epidemic simulator models a zombie outbreak in a closed population. Each day, zombies encounter humans at a rate proportional to both group sizes. Successful bites convert humans into zombies, so the horde grows while survivors shrink. The result is accelerating spread and a race toward human extinction.

How the Simulation Works

Each simulation day follows three steps. First, estimate daily bites as the infection rate multiplied by the current zombie count and human count, capped by humans still alive. Second, subtract those bites from the human population. Third, add the same number to the zombie population because every infected human joins the horde.

The daily bite formula is:

\(\text{bites} = \min(H,\lfloor r \times Z \times H \rfloor)\)

where \(H\) is humans, \(Z\) is zombies, and \(r\) is the infection rate coefficient. If humans reach zero before the selected number of days, the tool reports the extinction day. Otherwise it shows how many humans remain after the chosen time window. For a related predator-prey style model, try the Humans vs Vampires Calculator or the Among Us Impostor Odds Calculator.

Why Infection Rate Matters

A higher infection rate means more encounters turn into bites each day. Because bites depend on both zombies and humans, the outbreak accelerates once zombie numbers climb. Even a single starting zombie can overwhelm a large city when the rate is high enough. Lower rates buy survivors more time, but zombie numbers still compound quickly after the horde gains momentum.