Pack Years Calculator

A pack-year is the standard way to measure how much someone has smoked over a lifetime. One pack-year equals smoking one pack, defined as 20 cigarettes, every day for one year. It lets clinicians compare smoking histories on a single scale regardless of whether the habit was light and long or heavy and short.

Multiply the number of packs you smoked per day by the number of years you smoked. So pack-years equals packs per day times years smoked. If you count cigarettes instead of packs, divide your cigarettes per day by 20 first, since a standard pack holds 20 cigarettes. For example, 10 cigarettes a day for 40 years is 0.5 packs per day times 40, which is 20 pack-years.

Break your smoking history into periods where the amount stayed roughly the same, calculate pack-years for each period, then add them up. For instance, one pack a day for 10 years (10 pack-years) plus half a pack a day for 20 years (10 pack-years) totals 20 pack-years. This calculator handles one steady period at a time, so add the results together for an overall figure.

The US Preventive Services Task Force recommends that adults aged 50 to 80 with at least a 20 pack-year history talk to their doctor about yearly low-dose CT screening for lung cancer, if they currently smoke or quit within the past 15 years. Pack-years are only one factor, and your age and quit date matter too. This tool flags the 20 pack-year mark as a reference, not as a screening decision.

No. Pack-years measure only the time you were actually smoking, so leave out any stretch where you had stopped. If you smoked for 15 years, quit for 5, then smoked for another 10, count 25 years of smoking, not 30. Your quit date is tracked separately because some screening guidelines also consider how recently you smoked.

No. This calculator is for education only and is not a substitute for professional medical advice, diagnosis, or treatment. Use it to understand your smoking history, then discuss your individual risk and any screening or quitting plans with a qualified clinician.