Pack-year smoking history

Calculate cumulative tobacco exposure in pack-years, the standard measure used for lung cancer screening eligibility and risk assessment.

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What is this for?

A pack-year is one pack of twenty cigarettes smoked daily for one year. It is the standard way of expressing cumulative exposure, and it determines eligibility for low-dose CT lung cancer screening under current US recommendations.

How to use it

Select whether the patient reports cigarettes or packs per day, then enter the amount.
Enter the total number of years smoked. If intake varied substantially, calculate each period separately and add the pack-years together.
Add age and years since quitting to check eligibility for lung cancer screening.

Worked example

A 62-year-old patient has smoked one pack (20 cigarettes) a day for 30 years and still smokes. Calculate the pack-year history and check screening eligibility.

Answer: 20 ÷ 20 = 1 pack/day; 1 × 30 = 30 pack-years. Age 62 is within 50–80, exposure exceeds 20 pack-years, and they currently smoke — all three USPSTF criteria are met, so annual low-dose CT screening is recommended.

Clinical pearls & pitfalls

A pack is twenty cigarettes. Patients who report "half a pack" and those who report "ten a day" are describing the same exposure — confirm which they mean.
When intake changed over time, split the history into periods and sum the pack-years. Ten years at half a pack plus twenty years at two packs is 5 + 40 = 45 pack-years, not an average.
The 2021 USPSTF update lowered the threshold from 30 to 20 pack-years and the starting age from 55 to 50, substantially widening eligibility — particularly for Black patients and women, who develop lung cancer at lower cumulative exposures.
Pack-years capture cigarettes only. Cigars, pipes, waterpipe, and smokeless tobacco carry risk that this measure does not represent, and e-cigarette exposure has no equivalent metric.
Risk falls after quitting but does not return to that of a never-smoker. The 15-year window in the screening criteria reflects where the absolute benefit of screening becomes small.

Assumptions & limitations

Relies on self-report, which is subject to substantial recall error and systematic under-reporting.
Treats all cigarettes as equivalent, ignoring differences in tar yield, inhalation depth, and filter use.
Applies only to cigarettes. It cannot be extended to other tobacco or nicotine products.
The screening criteria shown are the USPSTF recommendation. Insurance coverage criteria and other national guidelines differ.

References

US Preventive Services Task Force. Screening for lung cancer: US Preventive Services Task Force recommendation statement. JAMA. 2021;325(10):962-970. link
National Lung Screening Trial Research Team. Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med. 2011;365(5):395-409.
Aldrich MC, et al. Evaluation of USPSTF lung cancer screening guidelines among African American adult smokers. JAMA Oncol. 2019;5(9):1318-1324.