Lung health
Pack-year calculator: your smoking history in pack-years
Enter how many cigarettes (or packs) you smoked per day and for how many years to get your smoking history in pack-years. One pack-year is 20 cigarettes a day for one year. Doctors use the number to decide who should be offered lung cancer screening: in the US, 20 pack-years is the threshold.
Enter your values above to see your result and what it means.
How to calculate pack-years
Pack-years = packs smoked per day × years smoked. A pack is 20 cigarettes, so 10 cigarettes a day is half a pack. Someone who smoked 15 cigarettes a day for 30 years has 0.75 × 30 = 22.5 pack-years. If your smoking changed over time, work out each period separately and add them up.
| Cigarettes per day | Years smoked | Pack-years |
|---|---|---|
| 10 | 20 | 10 |
| 20 | 10 | 10 |
| 20 | 20 | 20 |
| 15 | 30 | 22.5 |
| 40 | 15 | 30 |
| 30 | 25 | 37.5 |
Pack-years and lung cancer screening
In 2021 the US Preventive Services Task Force lowered its screening threshold from 30 to 20 pack-years and the starting age from 55 to 50. It recommends a yearly low-dose CT scan for adults aged 50 to 80 with at least 20 pack-years who currently smoke or quit within the past 15 years. Screening stops once a person has not smoked for 15 years or develops a health problem that substantially limits life expectancy or the ability to have lung surgery.
| Recommendation | Age | Smoking history | Quit within |
|---|---|---|---|
| USPSTF 2021 (current) | 50 to 80 | 20 pack-years or more | 15 years |
| USPSTF 2013 (replaced) | 55 to 80 | 30 pack-years or more | 15 years |
What pack-years do not capture
Pack-years multiply two numbers, so 40 cigarettes a day for 10 years and 20 a day for 20 years both come out at 20. The figure leaves out other things the USPSTF lists as lung cancer risk factors, such as age, the years since quitting, environmental exposures, earlier radiation therapy, other lung diseases and family history. It is a shorthand that lets doctors compare smoking histories quickly.
Frequently asked questions
How do you calculate pack-years?
Multiply the number of packs smoked per day by the number of years smoked. One pack is 20 cigarettes. For example, 1 pack a day for 20 years is 20 pack-years, and 10 cigarettes a day for 20 years is 10 pack-years.
What is 1 pack-year?
Smoking an average of 20 cigarettes, one pack, every day for one year.
How many pack-years qualify for lung cancer screening?
In the US, 20 pack-years or more, for adults aged 50 to 80 who still smoke or quit within the past 15 years (USPSTF 2021). The final decision is made with your doctor.
Do e-cigarettes or cigars count toward pack-years?
Pack-years are defined in cigarettes: one pack-year is 20 cigarettes a day for a year. Other tobacco products have no agreed conversion, so tell your doctor about them separately.
Do pack-years go down after I quit?
No. Pack-years count the total you smoked, so the number stays the same after you stop. What changes is the time since quitting, which screening rules also take into account.
Sources
- US Preventive Services Task Force. Lung Cancer: Screening. Final recommendation statement, March 9, 2021.
- US Preventive Services Task Force; Krist AH, Davidson KW, Mangione CM, et al. Screening for lung cancer: US Preventive Services Task Force recommendation statement. JAMA. 2021;325(10):962-970.
- Rozporządzenie Ministra Zdrowia z dnia 14 lipca 2026 r. zmieniające rozporządzenie w sprawie świadczeń gwarantowanych z zakresu programów zdrowotnych (Dz.U. 2026 poz. 976): Program badań przesiewowych raka płuca.