Calculate smoking pack-years from cigarettes per day and years smoked, with cumulative exposure category.
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One pack = 20 cigarettes
Packs per day
1.00
Years smoked
10
Est. total cigarettes
73,050
| Category | Pack-years |
|---|---|
| Light | < 10 |
| Moderate | 10–19 |
| Heavy | 20–39 |
| Very heavy | ≥ 40 |
A 30-pack-year history is often used as a clinical threshold for lung cancer screening eligibility in current or recent ex-smokers aged 50–80.
Pack-years = (cigarettes per day ÷ 20) × years smoked. Used in clinical contexts to quantify cumulative smoking exposure. Always discuss your individual risk with a healthcare professional.
Health — Medical
A pack-year is a standardised measure of cumulative tobacco exposure widely used in medicine to quantify smoking history. It combines how much you smoked with how long you smoked, helping clinicians assess risk for lung cancer, COPD, and cardiovascular disease.
One pack-year equals smoking one pack (20 cigarettes) per day for one year. The formula is: pack-years = (cigarettes per day ÷ 20) × years smoked. Smoking 10 cigarettes a day for 20 years and 20 cigarettes a day for 10 years both equal 10 pack-years.
Pack-years = (cigs/day ÷ 20) × years smoked
Standardised formula for quantifying cumulative tobacco exposure in clinical and epidemiological contexts.
Pack-year history is used in lung cancer screening — UK NHS and US USPSTF guidelines use a 20–30 pack-year threshold alongside age criteria for low-dose CT eligibility. It is also used in COPD diagnosis (significant history with symptoms warrants spirometry testing) and as an input in composite cardiovascular risk scoring tools.
Pack-year history is fixed — quitting does not reduce pack-years, but it substantially reduces ongoing risk. Lung cancer risk decreases significantly in the years following cessation, and cardiovascular risk approaches that of non-smokers within 5–15 years.
Frequently asked questions
Divide your average cigarettes per day by 20 to get packs per day, then multiply by years smoked. For example, 15 cigarettes/day for 20 years = 0.75 × 20 = 15 pack-years.
UK and US guidelines typically use 20–30 pack-years alongside age and current or recent smoking status as eligibility criteria for low-dose CT lung cancer screening. Your GP or doctor can confirm current local criteria.
No — pack-years represent cumulative exposure and are fixed regardless of quitting. However, stopping smoking significantly reduces future risk and is the most important step you can take for your health.
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