Pack-Year Calculator (Smoking History)
By Santaji GadepatilinUpdated October 27, 2026
How to use this calculator
Enter the average cigarettes per day and the number of years you smoked at that level. If your habit changed over time, calculate each period separately and add the results.
The formula
Pack-years = (cigarettes per day ÷ 20) × years smoked
Worked examples
- 20 cigarettes a day for 20 years = 20 pack-years
- 30 a day for 20 years = 30 pack-years
- 10 a day for 15 years, then 20 a day for 10 years = 7.5 + 10 = 17.5 pack-years
It’s never too late to quit
Risk starts to fall soon after stopping and keeps falling for years. Free support is available in most countries through national quit lines and health services — ask your doctor or pharmacist.
This calculator does not provide medical advice.
Frequently asked questions
What is a pack-year?
Smoking one pack of 20 cigarettes a day for one year. 10 cigarettes a day for 20 years is also 10 pack-years.
Why do doctors use pack-years?
It summarises lifetime smoking exposure. Higher values mean higher risk of lung cancer, COPD and heart disease.
Who is eligible for lung cancer screening?
The US Preventive Services Task Force (2021) recommends yearly low-dose CT screening for adults aged 50–80 with a 20 pack-year history who currently smoke or quit within the past 15 years. Rules differ by country.