On average, a single cigarette takes 20 minutes off a person’s life, according to a new study published at University College London. To put that into perspective, a pack of 20 cigarettes can shorten a person’s life expectancy by seven hours.

A team of behavioral scientists at University College London has found that for long-term smokers, just one cigarette reduces lifespan by approximately 20 minutes. They have published an editorial in the journal Addiction outlining their study that examined the lifespans of smokers in the U.

The estimated shortened life expectancy is more than what researchers first predicted in 2000, when they found that a cigarette can shorten a smoker's life expectancy by an average of 11 minutes. The data published in Addiction follow up on the 2000 study published in BMJ.

Research shows each cigarette smoked can reduce life expectancy by up to 22 minutes, highlighting the dangers of smoking.