How-to · Smoking history · Educational · Updated October 2, 2026
How do you calculate pack-years?
Direct answer
Pack-years = (cigarettes per day ÷ 20) × years smoked. One pack a day for one year is 1 pack-year, about 7,300 cigarettes. One pack a day for 30 years is 30 pack-years.
Common histories
| History | Packs/day | Pack-years |
|---|---|---|
| 1 pack a day for 20 years | 1 | 20 |
| 1 pack a day for 30 years | 1 | 30 |
| Half a pack (10) a day for 40 years | 0.5 | 20 |
| 10 cigarettes a day for 20 years | 0.5 | 10 |
| 15 cigarettes a day for 8 years | 0.75 | 6 |
| 2 packs a day for 25 years | 2 | 50 |
The Brinkman index is cigarettes per day × years, without dividing by 20. Thirty pack-years is a Brinkman index of 600.
When the amount changed
Add the periods. One pack a day for 10 years is 10 pack-years. Then 10 cigarettes a day for 15 years is 7.5. The total is 17.5 pack-years, not an average of the two daily amounts across 25 years.
Cigars are not one-for-one
Screening cutoffs use cigarette pack-years. Other tobacco is converted only as an exposure estimate: a large cigar is about 4 cigarettes, a cigarillo about 2, and a pipe bowl about 2.5. Two large cigars a day for 15 years is about 6 pack-year equivalents, shown separately from cigarettes. Vaping has no accepted pack-year conversion.
Limits
- Pack-years do not fall after you quit. They are a record of what you already smoked.
- There is no safe level. A total under a screening cutoff is not a clean bill of health.
- This page is education, not a lung-cancer diagnosis or a scan order.
Use the calculator
Screening cutoffs: how many pack-years for lung cancer screening? Enter each period in the pack-year calculator. Free quit help: 1-800-QUIT-NOW.