About the Pack Year Calculator
A pack-year is the standard way doctors summarise lifetime tobacco exposure: one pack-year equals smoking 20 cigarettes (one pack) a day for one year. Someone who smoked half a pack a day for 20 years and someone who smoked a pack a day for 10 years both have 10 pack-years.
Enter your average packs (or cigarettes) per day and the number of years you smoked. The calculator returns your pack-years and the approximate number of cigarettes smoked, and — using your age and smoking status — checks the 2021 US Preventive Services Task Force criteria for yearly low-dose CT lung cancer screening: age 50 to 80, at least 20 pack-years, and currently smoking or quit within the past 15 years.
If your smoking varied over time, calculate each period separately and add the pack-years together, or enter a realistic long-run average. Screening decisions should always be made with a clinician, who will also consider your overall health. Quitting at any age lowers risk.
With the default inputs, the pack-years is 20. Change any value above to recalculate instantly.
How to use the pack year calculator
- 1Choose whether to enter packs or cigarettes per day.
- 2Enter your average daily amount and the total years you smoked.
- 3Enter your age and whether you still smoke (and when you quit if not).
- 4Read your pack-years and the screening eligibility result.
Formula and method
One pack contains 20 cigarettes, so cigarettes per day are divided by 20 to get packs per day. Multiplying by the number of years smoked gives pack-years. The approximate number of cigarettes is packs per day × 20 × 365 × years.
Screening eligibility follows the USPSTF 2021 recommendation: adults aged 50 to 80 with at least a 20 pack-year history who currently smoke or quit within the past 15 years. Other organisations, such as the American Cancer Society, have since dropped the years-since-quitting limit, so talk to your clinician even if you narrowly miss these criteria.
- packs per day
- Average packs (20 cigarettes) smoked daily
- years smoked
- Total years of smoking, excluding smoke-free periods
Worked examples
One pack a day for 20 years, age 55
1 pack × 20 years = 20 pack-years, about 146,000 cigarettes. At 55 and still smoking, this meets all three USPSTF criteria.
15 cigarettes a day for 30 years
15 cigarettes is 0.75 of a pack, and 0.75 × 30 years = 22.5 pack-years, or about 164,250 cigarettes.
Former smoker who quit 18 years ago
1.5 packs × 20 years = 30 pack-years, well above 20, but quitting 18 years ago falls outside the USPSTF 15-year window.
Half a pack a day for 30 years
0.5 × 30 = 15 pack-years, below the 20 pack-year threshold for USPSTF screening.
Frequently asked questions
What is a pack-year?+
A pack-year is a unit of smoking exposure equal to smoking one pack of 20 cigarettes a day for one year. Two packs a day for 10 years and one pack a day for 20 years both equal 20 pack-years.
Who should get lung cancer screening?+
The USPSTF recommends yearly low-dose CT screening for adults aged 50 to 80 who have a 20 pack-year smoking history and currently smoke or have quit within the past 15 years.
How do I count pack-years if my smoking changed over time?+
Calculate each period separately — for example 0.5 packs for 10 years (5 pack-years) plus 1 pack for 15 years (15 pack-years) — and add them for a total of 20 pack-years.
Do cigars, pipes or vaping count?+
Pack-years are defined for cigarettes. Cigars, pipes and e-cigarettes carry their own risks but are not converted to pack-years for screening criteria; mention them to your clinician.
Does lung cancer risk fall after quitting?+
Yes. Risk declines steadily after quitting, although it stays higher than for people who never smoked for many years. Quitting also quickly benefits heart and lung health.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.