Enter the age smoking started, then either the age it stopped or the current age if smoking has not stopped yet. The main result is tied to the age of cessation rather than to a generic timeline shared by every visitor. For example, someone who started at 17 and quit at 40 is estimated to have avoided about 90 percent of the excess mortality risk linked to continued smoking; that quit age is associated with roughly 9 additional years of population-level life expectancy compared with continued smoking. This version uses quit age as the main calculation input because that is how the long-term findings behind the model report the benefit; smoking duration is displayed as context rather than used to create an unsupported adjustment.

The percentage shown is the share of excess risk avoided, meaning the extra risk that continued smoking adds on top of the baseline risk of a never-smoker – not the absolute risk of death from any cause.

The evidence strength label next to the main result shows how directly the estimate is supported at that particular age. Ages that land exactly on 30 or 40 draw on two large long-term cohort studies that reported closely similar figures, so those are marked strong. Ages in between are a straight-line estimate between two solid points, marked one step down, since no study reports a figure for those exact in-between ages. Ages past 60 rely on a smoothed estimate rather than a directly reported number and are marked as limited, model-based evidence.

Below the main numbers, a chart illustrates three lines across age: a flat baseline for someone who never smoked, a line for continued smoking, and a line for the entered scenario that follows continued smoking up to the quit age and then bends back toward the baseline. The two lines move closer together after the quit age but a visible gap remains – that gap is intentional. Quitting substantially narrows the gap from a never-smoker reference, but does not necessarily remove it completely. The chart is a simplified illustration of that gap, not a plotted measurement of risk at every age.

If the current age is entered because smoking has not stopped, a row below the chart shows what changes by waiting: the estimated benefit at quitting now, compared with quitting 3, 6, or 10 years later, along with how much of that benefit and how many life-years would be given up by waiting. If the age already entered is a quit age, that row is replaced by a short note on where that age sits relative to the main research milestones.

A separate, collapsed section lists the more familiar physical recovery milestones – circulation, lung function, and short-term heart risk – for anyone who wants that layer as well. It stays secondary because the age-based population estimate above is the main purpose of this tool.

This calculator provides population-level estimates and cannot predict any individual’s personal risk, lifespan, or health outcome. Genetics, overall health, and other exposures all affect individual results. It is not medical advice. The core figures come from two large long-term cohort studies that each reported closely similar benefit at quitting before age 30 and before age 40: Doll R, Peto R, Boreham J, Sutherland I, “Mortality in relation to smoking: 50 years’ observations on male British doctors,” BMJ 2004;328:1519, and Pirie K, Peto R, Reeves GK, Green J, Beral V, “The 21st century hazards of smoking and benefits of stopping,” Lancet 2013;381:133-141. The age-50 estimate is a single-source summary from the Clinical Trial Service Unit, Oxford. Physical recovery milestones follow CDC guidance on the benefits of quitting. Anyone planning to quit smoking should talk to a doctor or a smoking cessation service for personalized support.