CNET: How long will your body allow you to survive on short sleep? And what about complete lack of sleep — can it really kill you? 

There’s no solid answer to the question of how long humans can survive without sleeping. Apparently, people can live a rather long time with zero sleep, as proved by Randy Gardner and other people who intentionally deprived themselves of sleep for record-breaking purposes. 

It’s clear that ill effects start to set in after just one day of total sleep deprivation and after a couple of nights of partial sleep deprivation, so it’s best to always strive to get as much sleep as possible.