Pack-Years Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026A standard way to compare smoking histories
One pack-year represents smoking one pack (20 cigarettes) per day for one full year - this standardized measure lets clinicians compare very different smoking patterns (fewer cigarettes over many years, or more cigarettes over fewer years) using a single comparable figure.
Worked example
For someone smoking 20 cigarettes per day for 15 years:
Pack-Years = (20 / 20) x 15 = 15.0 pack-years
Frequently asked questions
Why does pack-year history matter clinically? Pack-year history is commonly used to help determine eligibility for lung cancer screening programs (which often use specific pack-year thresholds) and to assess cardiovascular and respiratory disease risk more broadly.
How should someone with a variable smoking history calculate this? For smoking histories that changed significantly over time (increasing or decreasing cigarettes per day), calculate pack-years separately for each distinct period and add the results together for the most accurate total.
This is an informational tool only, not a substitute for professional medical assessment - discuss your specific smoking history and screening eligibility with a qualified healthcare provider.