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.

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.