How Smoking Affects Life Expectancy

Smoking is the single largest preventable cause of early death in the world. According to CDC mortality data and decades of cohort research, lifelong smokers lose roughly a decade of life on average compared to people who never smoked. This page summarises what the underlying studies actually say, how the cost scales with intensity and duration, what quitting recovers and on what timeline, and how Your Death Timer encodes the effect in its lifestyle adjustment.

The scale of the effect

The clearest evidence comes from the British Doctors Study, a 50-year cohort that followed nearly 35,000 male physicians. Richard Doll and Richard Peto's analysis showed that men who smoked throughout adult life died on average about ten years earlier than lifelong non-smokers. Subsequent work in the US Million Person Study and the UK Million Women Study confirmed the same order of magnitude in both sexes: heavy lifelong smokers lose 10–11 years, moderate smokers lose 6–8 years, and light smokers still lose around 4 years.

These are averages across large populations. Some heavy smokers reach their nineties; many die in their fifties from heart disease, lung cancer, COPD or stroke. Smoking shifts the entire distribution of lifespans to the left, not just the unlucky tail.

Dose-response: cigarettes per day and pack-years

The harm scales with both how much you smoke per day and how many years you have smoked for. Epidemiologists combine the two into a unit called the pack-year: one pack-year equals smoking 20 cigarettes per day for one year, so a 10-cigarette-per-day habit for 20 years is 10 pack-years.

• Heavy smoker (10+ cigarettes/day for decades): roughly 8 years lost on average.
• Light smoker (under 10/day): roughly 4 years lost.
• Occasional or social smoker: roughly 2 years lost.
• Ex-smoker who quit 5+ years ago: about 0.5 years lost — most of the risk recovered.
• Never smoked: baseline.

One persistent myth is that "social" smoking — a few cigarettes at parties or with drinks — is essentially harmless. The data disagree. Even one to four cigarettes per day raises all-cause mortality measurably, particularly cardiovascular mortality, because the inflammatory and endothelial damage from tobacco smoke does not have a clean lower threshold.

Quitting reverses most of the risk

The most encouraging finding in the smoking-mortality literature is how much benefit quitting delivers — and how quickly. Within weeks of stopping, blood pressure and circulation improve. Within a year, the excess risk of coronary heart disease is roughly halved. By five years, stroke risk approaches that of a never-smoker. At ten to fifteen years out, lung cancer risk has fallen to about half that of a continuing smoker, and overall mortality risk is close to baseline.

The single most powerful finding comes from a 2013 New England Journal of Medicine analysis: people who quit before age 40 avoid roughly 90% of the excess mortality risk from continued smoking. Quitting at 50 still recovers about two-thirds of the risk; quitting at 60 still adds meaningful years. There is no age at which quitting fails to improve the odds.

Secondhand smoke and vaping

Long-term exposure to secondhand smoke — for example, growing up in a smoking household or working in pre-ban bars and restaurants — raises lung cancer risk by 20–30% and coronary heart disease risk by a similar amount. The effect on life expectancy is smaller than for active smoking, but it is real.

E-cigarettes are too new for definitive life-expectancy data. The current scientific consensus is that vaping is substantially less harmful than combustible tobacco — there is no tar and no combustion byproducts — but it is not risk-free, particularly for adolescents and for cardiovascular health. The calculator currently treats vaping as equivalent to light smoking, which may prove conservative as long-term data accrues.

How Your Death Timer encodes smoking

The smoking adjustment in the calculator maps the categories above directly onto year deltas drawn from the cited literature: −8 years for heavy smokers, −4 for light smokers, −2 for occasional smokers, −0.5 for long-quit ex-smokers, and zero for never-smokers. The adjustment is applied after the age-conditional baseline, so a 70-year-old smoker is penalised against the conditional remaining years for a 70-year-old of their country and gender, not against the at-birth average.