Pack-Years Calculator
Calculate pack-years of smoking history from packs per day and years smoked with this free health calculator that runs in your browser.
Enter Values
Minimum 0
Minimum 0
How to use this calculator
- Enter cigarettes per day and years smoked.
- Read the pack-years.
How it works
Pack-years = (cigarettes per day ÷ 20) × years smoked.
Worked example
20/day for 10 years. = 10 pack-years.
Common mistakes
- Assuming a pack is always 20 — adjust if yours differs.
- Averaging unevenly — use your typical daily amount.
Frequently asked questions
What is one pack-year?
One pack-year equals smoking 20 cigarettes a day for one year — or any equivalent, such as 40 a day for six months.
Why do doctors use pack-years?
It standardises lifetime tobacco exposure and helps decide who should be screened for lung cancer and COPD.
Why do clinicians use pack-years?
It standardises smoking history into one number to help assess risk. This tool is educational, not medical advice.
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Cite this tool
Zerdly. (2026). Pack-Years Calculator. Retrieved from https://www.zerdly.com/tools/pack-years-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.