Health

Pack Year Calculator

Calculate your smoking pack-years from cigarettes per day and years smoked. A key measure of cumulative tobacco exposure used in health screening.

Pack Year Calculator

Cigarettes per day

Years smoked

Method

How this calculator works

Pack-years = (cigarettes per day ÷ 20) × years smoked. One pack is defined as 20 cigarettes, so smoking one pack daily for one year equals one pack-year.

Enter the average number of cigarettes you smoke (or smoked) per day.
Enter the total number of years you have smoked.
The tool divides cigarettes per day by 20 to get packs per day, then multiplies by years smoked.
Read your total pack-years and the risk-context note below the result.

Examples

Worked examples

Real numbers, end-to-end results.

20 cigarettes/day for 15 years

= 15.0 pack-years

One full pack a day for 15 years equals exactly 15 pack-years.

10 cigarettes/day for 30 years

= 15.0 pack-years

Half a pack a day over a longer period gives the same cumulative exposure.

40 cigarettes/day for 25 years

= 50.0 pack-years

Two packs a day for 25 years is a substantial smoking history.

Use cases

When to use it

Estimating cumulative tobacco exposure for a health check-up
Checking eligibility criteria for lung cancer screening discussions
Tracking your smoking history before and after quitting
Providing an accurate history to your doctor or clinician

Disclaimer: This calculator provides estimates for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for decisions affecting your health. Results depend on the accuracy of inputs provided.

FAQ

Frequently asked questions

What is a pack-year?

A pack-year is a standardized measure of how much someone has smoked over time. One pack-year equals smoking one pack (20 cigarettes) per day for one year.

How are pack-years calculated?

Pack-years = (cigarettes per day ÷ 20) × number of years smoked. For example, 10 cigarettes a day for 20 years is (10/20) × 20 = 10 pack-years.

Why do pack-years matter?

Pack-years estimate cumulative tobacco exposure and help clinicians assess risk for lung cancer, COPD, and other smoking-related diseases. Lung cancer screening guidelines often use a 20-pack-year threshold.

What counts as a heavy smoking history?

Many guidelines consider a history of 20 or more pack-years significant, and 30 or more pack-years is often used as a threshold for recommending low-dose CT lung cancer screening in eligible adults.

Does quitting reduce my pack-years?

No. Pack-years measure past cumulative exposure, so the number does not decrease after you quit. However, quitting immediately begins to lower your ongoing risk of many smoking-related diseases.