# Pack-year

Source: https://onco.cc/terms/pack-year/  
OnCo record `pack-year` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The unit used to measure how much someone has smoked over a lifetime: one pack-year is twenty cigarettes a day for one year. Twenty a day for thirty years, or forty a day for fifteen, are both thirty pack-years.

## Summary

A pack-year multiplies the number of packs smoked a day by the number of years of smoking, taking a pack as twenty cigarettes. It is the measure every lung cancer screening rule is written in. The National Lung Screening Trial enrolled people with at least 30 pack-years who smoked or had stopped within 15 years; the US Preventive Services Task Force set its 2013 threshold at 30 pack-years and ages 55 to 80, and lowered it in 2021 to 20 pack-years and ages 50 to 80, a change that widened eligibility substantially and was aimed in part at groups whose lung cancer arises at lower cumulative exposure. England's programme does not use a pack-year cut-off at all: it feeds smoking duration and intensity, with age, body mass index, education, family history and lung disease, into a risk model and screens above a predicted-risk threshold. The unit has a known weakness: it treats twenty a day for thirty years and sixty a day for ten as equivalent, when duration raises lung cancer risk more steeply than intensity does.

## Fields

- Kind: Term
- Last checked: 2026-09-25
- Also known as: pack years; pack-years; packyear; cigarette pack-year; smoking pack-year
- Tags: lung

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Pack-year
- US Preventive Services Task Force, JAMA 2021: screening for lung cancer, recommendation statement (annual low-dose CT at 50 to 80 with 20 pack-years, grade B): https://doi.org/10.1001/jama.2021.1117
- National Lung Screening Trial Research Team, N Engl J Med 2011: reduced lung-cancer mortality with low-dose computed tomographic screening (53,454 people): https://doi.org/10.1056/nejmoa1102873
- Cancer Epidemiol 2023: the value of blood-based measures of liver function and urate in lung cancer risk prediction (388,199 UK Biobank participants; the 1.51 percent six-year threshold): https://doi.org/10.1016/j.canep.2023.102354
- CRUK: lung cancer risk factors (attributable fractions for the UK): https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/lung-cancer/risk-factors

## Connected records

- cancers: [Lung cancer (all types)](https://onco.cc/cancers/lung-cancer/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Small-cell lung cancer](https://onco.cc/cancers/sclc/)
- technologies: [Low-dose CT lung screening](https://onco.cc/technologies/low-dose-ct-screening/), [NHS Targeted Lung Health Check (lung cancer screening programme)](https://onco.cc/technologies/nhs-targeted-lung-health-check/)
- terms: [Lung cancer in never-smokers](https://onco.cc/terms/never-smoker-lung-cancer/), [Lung-RADS and nodule reporting](https://onco.cc/terms/lung-rads/), [Pulmonary nodule](https://onco.cc/terms/pulmonary-nodule/), [Radon](https://onco.cc/terms/radon/), [Stopping smoking](https://onco.cc/terms/smoking-cessation/), [Targeted lung health check](https://onco.cc/terms/targeted-lung-health-check/)

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