If you’re thinking about making a New Year’s resolution to quit smoking, it might help to know that new research says it could extend your life expectancy.

Each cigarette someone smokes, on average, can take about 20 minutes off their life expectancy overall, according to new research based on British smokers.

After accounting for socioeconomic status and other factors, researchers at University College London estimated the loss of life expectancy per cigarette at about 17 minutes for men and 22 for women, they wrote in an editorial published Sunday in the journal Addiction.

That means if someone smokes a pack of 20 cigarettes per day, “20 cigarettes at 20 minutes per cigarette works out to be almost seven hours of life lost per pack,” said Dr. Sarah Jackson, a principal research fellow in the UCL Alcohol and Tobacco Research Group and lead author of the paper.

“The time they’re losing is time that they could be spending with their loved ones in fairly good health,” Jackson said.

“With smoking, it doesn’t eat into the later period of your life that tends to be lived in poorer health. Rather, it seems to erode some relatively healthier section in the middle of life,” she said. “So when we’re talking about loss of life expectancy, life expectancy would tend to be lived in relatively good health.”

The research, which was commissioned by the UK Department for Health and Social Care, includes mortality data on men from the British Doctors Study and data on women from the Million Women Study. These studies found that on average, people who smoked throughout their lives lost around 10 years of life compared with people who never smoked.

Similarly, in the United States, life expectancy for smokers is estimated to be at least 10 years shorter than for nonsmokers, according to the US Centers for Disease Control and Prevention.

Overall, the new data from the UK indicates that the harm caused by smoking appears to be cumulative. And the amount of life expectancy that can be recovered by quitting may depend on several factors, such as age and how long someone has smoked.

“In terms of regaining this life lost, it’s complicated,” Jackson said.

“These studies have shown that people who quit at a very young age – so by their 20s or early 30s – tend to have a similar life expectancy to people who have never smoked. But as you get older, you progressively lose a little bit more that you then can’t regain by quitting,” she said. “But no matter how old you are when you quit, you will always have a longer life expectancy than if you had continued to smoke. So, in effect, while you may not be reversing the life lost already, you’re preventing further loss of life expectancy.”

In their paper, Jackson and her colleagues wrote that a person smoking 10 cigarettes per day who quits smoking on January 1 could prevent the loss of a full day of life by January 8. They could prevent loss of a full week of life by February 20 and a full month by August 5. By the end of the year, they could have avoided losing 50 days of life expectancy.

“Stopping smoking is, without a doubt, the best thing you can do for your health,” Jackson said. “And the sooner you stop smoking, the longer you’ll live.”

Although smoking rates have been declining since the 1960s, cigarette smoking remains the leading cause of preventable disease and death in the United States, killing more than 480,000 Americans each year. But quitting before age 40 can reduce the risk of dying from smoking-related disease by about 90%, according to the CDC.

A separate study, published last year in the journal Nature, found that smoking can have both short-term and long-term effects on a person’s immune system, leaving them vulnerable to the risk of developing infections, cancers or autoimmune diseases. The study also found that the more someone smoked, the more it changed their immune response.

When smokers in the study quit, their immune response got better at one level, but it didn’t completely recover for years, according to study co-author Dr. Darragh Duffy, who leads the Translational Immunology unit at the Institut Pasteur.

“The good news is, it does begin to reset,” he said when the study was released. “It’s never a good time to start smoking, but if you’re a smoker, the best time to stop is now.”