How much does smoking shorten your life?
At age 40, the difference between the best and worst answer here is about 12.0 years of life expectancy — 12.5 for men and 11.5 for women. That is the gap between “never smoked” and “over a pack a day”, holding everything else constant.
Smoking is the largest single number in this entire model, and it is not close. It is also the one where the evidence is strongest: the relationship has been followed in the same people for more than fifty years, which almost nothing else in lifestyle epidemiology can claim.
What each answer costs, at 40
| Answer | Hazard ratio | Years vs. best |
|---|---|---|
| Never smoked | 0.88 | best |
| Quit over 10 years ago | 1.00 | −1.3 |
| Vape only(evidence still thin) | 1.20 | −3.2 |
| Quit within 10 years | 1.22 | −3.3 |
| Under 10 a day | 1.75 | −7.1 |
| 10–20 a day | 2.30 | −9.9 |
| Over a pack a day | 2.85 | −12.1 |
Computed from the SSA 2023 period life table with this factor’s hazard ratio applied and every other factor held neutral. Source: Jha et al., NEJM 2013; Doll et al., BMJ 2004.
Does it matter less as you get older?
Yes, and by a lot. A hazard ratio applies to the years you have left, so the same answer costs less in absolute terms the later you are asked it. That is an argument for changing it early, not for concluding it no longer matters.
| If you are now | Men | Women |
|---|---|---|
| 30 years old | 13.7 yrs | 12.3 yrs |
| 40 years old | 12.5 yrs | 11.5 yrs |
| 50 years old | 11.1 yrs | 10.6 yrs |
| 60 years old | 9.3 yrs | 9.2 yrs |
| 70 years old | 7.1 yrs | 7.4 yrs |
What the evidence actually shows
The landmark figure comes from Jha and colleagues in the New England Journal of Medicine, who followed more than 200,000 American adults and found that lifelong smokers lose roughly ten years of life compared with people who never smoked. Doll's fifty-year follow-up of British doctors reached the same conclusion from an entirely separate cohort. Crucially, both found that quitting works, and that it works better the earlier it happens — stopping before 40 avoids around 90% of the excess risk, and stopping before 35 returns almost all of it.
What to do about it
Quitting is the single largest lever on this page. Ten years smoke-free returns most of the excess risk; quitting before 40 avoids about 90% of it.
Where this number is weak
The model treats vaping as carrying about a quarter of the excess risk of light smoking, but that figure is the shakiest number on this page. Nicotine vapour has not existed long enough for anyone to have followed a cohort to death, so any confident claim about its long-term mortality effect — in either direction — is currently unsupported.
More generally: these are observational cohorts, which show association rather than proof of cause. The full methodology sets out every simplification the model makes.
What is it costing you?
The calculator weighs this against your other nine factors and ranks them.
Then make it count. The Extension Plan turns your result into a 12-week plan, starting with the habit worth the most years to you · $9. See what is in it →