One pack year equals smoking 20 cigarettes a day for one year. U.S. guidelines recommend yearly low-dose CT screening for adults aged 50–80 with 20 or more pack years.
How to use the Pack Year Calculator
- Cigarettes per day
- Years smoked
Results update as you type, and every field accepts the units shown in its menu.
How it works
Convert cigarettes per day into packs and multiply by the number of years.
Inputs explained
| Field | What to enter |
|---|---|
| Cigarettes per day | A number |
| Years smoked | A number |
Example values
How the main result changes when Cigarettes per day changes and everything else stays at the example values above:
| Cigarettes per day | Pack years |
|---|---|
| 7.5 | 9.4 |
| 11.25 | 14.1 |
| 15 | 18.8 |
| 18.75 | 23.4 |
| 22.5 | 28.1 |
| 30 | 37.5 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Pack years = (cigarettes per day ÷ 20) × years smokedWorked example
Inputs — Cigarettes per day: 15; Years smoked: 25.
Results — Pack years = 18.8.
Frequently asked questions
Does quitting reset pack years?
No, pack years record past exposure, but risk falls over time after quitting.
Where can I get help to quit?
Your doctor or a national quitline can help.
What formula does the Pack Year Calculator use?
Pack years = (cigarettes per day ÷ 20) × years smoked.