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Pack-Years Smoking History

Pack-years = packs smoked per day × years smoked (1 pack = 20 cigarettes). USPSTF 2021 recommends annual low-dose CT lung cancer screening for adults 50–80 with ≥20 pack-years who smoke now or quit within 15 years.

  • Packs per day (packs/day or cigarettes/day)
  • Years smoked (years)
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Interpretation

ResultMeaning
< 20Below USPSTF screening threshold
≥ 20Meets pack-year criterion for LDCT screening (age 50–80, current or quit <15 y)

Formula

Pack-years = (cigarettes per day ÷ 20) × years smoked

Clinical pearls

  • For variable smoking, sum each period separately (e.g. 1 ppd × 10 y + 0.5 ppd × 20 y = 20 pack-years).
  • Pack-years understate risk from long duration at low intensity; duration matters more than intensity for lung cancer.

Examples

pack years 1.5 ppd for 20 years20 cigarettes a day for 30 years pack yearssmoking history half a pack a day for 35 years

FAQ

How do you calculate pack-years?

Multiply the number of packs smoked per day by the number of years smoked. 20 cigarettes a day for 30 years is 30 pack-years.

How many pack-years for lung cancer screening?

USPSTF 2021: 20 pack-years or more, age 50–80, currently smoking or quit within the past 15 years.

Evidence

  1. US Preventive Services Task Force. Screening for lung cancer: USPSTF recommendation statement. JAMA 2021;325:962–70.

General & Anthropometrics · Reviewed 2026-10-14 · Methodology