How Long Would A Zombie Apocalypse Actually Last?

There are plenty of questions that come up when considering the inevitable zombie apocalypse that's undoubtedly on its way. Which Walmart are you going to loot first? When your significant other gets turned, do you put them out of their misery immediately or keep them alive long enough to find out if you'll still get gifts from their family over the holidays? Will the Cranberries keep playing that song, or will that seem distasteful? And, for the sake of preparedness, how long is this thing going to last?

Bad news for your longevity but good news for your doomsday prepping grocery budget: a zombie outbreak would last a little over three months before wiping out effectively everyone. This news comes to us via a 2015 study published by the British Medical Journal... maybe this is what they study on their slow days.

The timeline of a zombie apocalypse

The report, titled "Zombie infections: epidemiology, treatment, and prevention," made use of the SIR compartmental epidemiology model, which is something you can parrot back to your friends if you ever think they're starting to suspect that you're not very smart. SIR makes use of three potential categories of living beings in a rhetorical outbreak scenario: the Susceptible, the Infected, and the Recovered. Dividing people into these categories and assuming a 90% successful infection rate for each individual shambling corpse, the study showed that the planet would be down to just about 300 uninfected humans by day 100.

A couple of things to keep in mind. Number one, the initial report didn't take into account the possibility that humans would fight back, spitting in the face of decades of Romero movies. When they factored in a 10 percent chance that each survivor would kill a zombie every day, the outlook remained grim, but the undead were all un-undead by about three years in, with the population of the planet slowly kicking back into gear in the years that (hypothetically) followed. 

Number two: the whole thing was sort of a goof perpetrated in the name of raising awareness of disaster preparedness, so keep your chin up, killer.