Pack Year Calculator
Measure lifetime smoking exposure in pack-years, used to decide on lung cancer screening.
About the Pack Year Calculator
A pack-year is smoking 20 cigarettes (one pack) a day for one year. The US Preventive Services Task Force (2021) recommends yearly low-dose CT lung cancer screening for adults aged 50–80 with at least 20 pack-years who currently smoke or quit within the past 15 years.
The formula
Pack-years = (cigarettes per day ÷ 20) × years smoked
Worked example
Example: Pack-years = 18.7
- Inputs: Cigarettes per day: 22; Years smoked: 17 years.
- Formula: Pack-years = (cigarettes per day ÷ 20) × years smoked
- Result: Pack-years = 18.7
Things to keep in mind
- This is an estimate for general information, not medical advice. Talk to a doctor or other qualified professional about your health.
Questions people ask
Is it ever too late to quit?
No. Risk of heart disease drops within a year of quitting, and lung cancer risk falls steadily.
How do I count pack-years if my smoking changed over time?
Work out the pack-years for each period separately (packs a day × years) and add them up.