About this tool
Pack-years is a standardized way doctors and researchers quantify a person's cumulative smoking exposure, so that a history of two very different smoking patterns can be compared on the same scale. The formula is simple: divide the average number of cigarettes smoked per day by 20 (the number of cigarettes in one standard pack), then multiply by the number of years that pattern was smoked — packYears = (cigarettesPerDay / 20) × yearsSmoked. Someone who smoked a pack a day (20 cigarettes) for 10 years has a 10 pack-year history; someone who smoked half a pack a day for 20 years also reaches 10 pack-years, even though the daily habit looked very different.
Few smoking histories are perfectly constant, though — habits often change: fewer cigarettes during one stretch, more during another, a period of quitting and restarting. This calculator lets you enter each distinct period separately and adds up the pack-years across all of them, which is both more accurate and closer to how clinicians actually ask about smoking history in a medical visit. Keep in mind that pack-years is a quantification of exposure, not a diagnostic score or a risk prediction on its own — clinicians weigh it alongside age, family history, other exposures and many other factors. This tool runs entirely in your browser; nothing you enter is uploaded or stored anywhere but your own device.
Frequently asked questions
What is pack-years actually used for?
Clinicians commonly record pack-years as part of a standard medical history, since it gives a single, comparable number to quantify cumulative smoking exposure regardless of whether someone smoked heavily for a short time or lightly for a long time. It has been used in various research contexts as one factor (among many others) that correlates with smoking-related health risks, and it's a common threshold criterion in some lung-cancer screening guidelines. It does NOT diagnose anything by itself — it's a standardized way to document a piece of medical history, similar to how "blood pressure reading" documents one measurement without being a diagnosis on its own.
How do I count a period where I switched between cigarette brands or types?
The standard pack-years formula counts CIGARETTES per day, not brands or specific product types (it doesn't distinguish between light/regular/menthol cigarettes, for example — this is one of the known simplifications of the metric). If your daily cigarette count stayed roughly the same across a brand switch, you can treat it as one continuous period; if the switch coincided with a real change in how much you smoked per day, split it into separate periods using this tool's "add another period" feature, using your best honest estimate of average daily cigarettes for each distinct period.