Pack-Years Calculator
Pack-years summarize cumulative smoking exposure and are used in screening guidelines, but this figure is an estimate, not medical advice or a diagnosis. Discuss your smoking history and any screening with a healthcare professional.
A pack-year is a standard unit clinicians use to quantify how much tobacco a person has smoked over their lifetime, where one pack-year equals smoking 20 cigarettes a day for one year. This calculator converts your daily cigarette count and the number of years you smoked into pack-years, since cumulative exposure — not just current habits — drives many smoking-related risks and screening decisions.
Formula
pack-years = (cigarettes per day / 20) x years smoked
- cigarettes per day
- Average cigarettes smoked each day
- 20
- Cigarettes in one standard pack
- years smoked
- Total number of years smoking
How it works
- Enter the average number of cigarettes you smoke per day and the total number of years you have smoked.
- The calculator divides cigarettes per day by 20 (one pack) to get packs per day, then multiplies by the years smoked.
- It shows your pack-years plus a broad risk band: under 10, 10-30, or 30+ pack-years, the last of which appears in many lung-screening criteria.
Worked example
Someone who smoked one pack a day for 20 years calculates their pack-years.
- Packs per day = 20 / 20 = 1.
- Pack-years = 1 x 20 = 20.
- Twenty pack-years falls in the moderate (10-30) band.
20 pack-years, equal to one pack per day for two decades.
Frequently asked questions
- What exactly is one pack-year?
- One pack-year equals smoking 20 cigarettes (one pack) per day for one year. Twenty cigarettes a day for two years, or 40 a day for one year, both equal two pack-years.
- How do I handle a habit that changed over time?
- For varying habits, add up pack-years for each period separately, then sum them. For example, half a pack a day for 10 years (5 pack-years) plus one pack a day for 10 years (10) totals 15 pack-years.
- Why do pack-years matter for lung cancer screening?
- Many guidelines recommend low-dose CT screening for adults with a heavy smoking history, often around 20 or more pack-years combined with age and recency criteria. Pack-years give clinicians a consistent measure of that cumulative exposure.
- Is this calculator a substitute for medical advice?
- No. It is an educational estimate of cumulative tobacco exposure, not medical advice, a diagnosis, or a screening recommendation. Talk to a healthcare professional about your smoking history and any appropriate screening.