Medical & Clinical
Pack-Years Calculator
Two simple answers — how much, for how long — become the single number that decides lung-cancer screening eligibility.
Pack-years quantify lifetime smoking: packs per day × years smoked. One pack-year equals 20 cigarettes daily for a year. A history of 20 pack-years or more in a 50–80-year-old is the classic threshold for lung-cancer screening eligibility. Interpretation belongs to your clinician — use these numbers to ask better questions.
Pack-years = packs/day × years.
20 pack-years = screening threshold.
Quitting stops the counter — not the risk.
Calculate Your Pack-Years
Pack-Years
What Is Pack-Years?
Pack-years condense a smoking history into one number: one pack-year equals smoking a pack (20 cigarettes) daily for one year — or the equivalent, like half a pack for two years.
The measure matters because dose drives disease: lung cancer, COPD, and heart disease all scale with cumulative exposure. It also gates lung-cancer screening — USPSTF recommends annual low-dose CT for 50–80-year-olds with 20+ pack-years who smoke or quit within 15 years.
How It Is Calculated
Pack-years = (cigarettes per day ÷ 20) × years smoked
Example: Example: 20/day for 20 years → 20 pack-years (screening-eligible range)
Exposure bands
| Pack-years | Category |
|---|---|
| 0 | Never smoker |
| < 10 | Light |
| 10–20 | Moderate |
| 20–40 | Heavy |
| 40+ | Very heavy |
Limitations
- Self-reported history is approximate — people underestimate.
- Risk from quitting declines over years but never fully resets.
- Screening criteria also require age 50–80 and smoking within 15 years.
Sources & Review
References used for this calculator’s formulas and thresholds:
Pack-Years FAQ
How are pack-years calculated?
Multiply packs per day by years smoked — 20 cigarettes daily for 20 years is 20 pack-years.
What pack-years qualify for lung screening?
20 or more, combined with age 50–80 and smoking within the past 15 years, meets the classic USPSTF screening window.
Do pack-years reset after quitting?
The counter stops, but risk declines gradually — after 15 years smoke-free, risk is roughly halved, never zero.
Important disclaimer: Results are educational estimates, not a substitute for professional medical advice. Discuss your results with a qualified professional before making decisions.