Pack Years Calculator
Calculate pack-years from cigarettes or packs per day and years smoked.
Pack-years = packs smoked per day × years smoked, where one pack is 20 cigarettes. Smoking 1 pack a day for 30 years, or 2 packs a day for 15 years, is 30 pack-years.
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How to use it
- Enter how much you smoked per day, in cigarettes or packs.
- Enter the number of years you smoked at that level.
- Read your pack-years and screening guidance.
What you enter
- Cigarettes or packs per day
- Years smoked
What you get
- Pack-years
- Screening guidance
Formula
Pack-years = (cigarettes per day ÷ 20) × years smoked
Worked example
Input: 20 cigarettes a day for 30 years
Result: 30 pack-years
Meets the 20 pack-year threshold for yearly lung cancer screening if aged 50–80.
Questions
How do you calculate pack-years?
Multiply packs per day by years smoked. Ten cigarettes a day (half a pack) for 20 years is 10 pack-years.
Who should get lung cancer screening?
The USPSTF recommends a yearly low-dose CT scan for adults aged 50–80 with 20 or more pack-years who smoke now or quit within the past 15 years.
Does quitting reset pack-years?
No, pack-years are a lifetime total. But risk falls steadily after quitting, and the screening rule stops applying 15 years after you quit.
How do I count periods when I smoked different amounts?
Calculate pack-years for each period and add them together.
Limitations
- Screening decisions also depend on health status and shared decision-making with a clinician.
References
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