Pack-year calculator
Enter how many cigarettes a day you smoked and for how many years. If the amount changed, add a second period. You get pack-years, the measure doctors use for smoking history, along with the Brinkman index and an estimate of cigarettes smoked. The result is for information only.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the average number of cigarettes a day and the years you smoked that much.
- If the amount changed, for example from 20 to 10 a day, tick the box and enter the second period.
- Read pack-years, the Brinkman index and the approximate number of cigarettes.
- Pack-years = cigarettes per day ÷ 20 × years, summed over the periods
- Brinkman index = cigarettes per day × years
- Cigarettes in total ≈ cigarettes per day × 365 × years
Worked example
15 cigarettes a day for 30 years: 15 ÷ 20 × 30 = 0.75 × 30 = 22.5 pack-years. The Brinkman index is 15 × 30 = 450, and the total is about 450 × 365 = 164,250 cigarettes.
With two periods, a pack a day for 10 years and then 10 a day for 5 years: 10 + 0.5 × 5 = 12.5 pack-years.
Tips
- Leave out the years when you did not smoke; pack-years count only smoking time.
- Past smoking still counts after quitting: pack-years never go down, but risk falls over the years after you stop.
- Doctors use pack-years together with age and the years since quitting; the number alone is not a risk estimate.
- Information only. For help to stop smoking, talk to a doctor, a pharmacist or a stop-smoking service.
Frequently asked questions
How are pack-years calculated?
Pack-years = cigarettes per day ÷ 20 × years smoked. One pack-year is 20 cigarettes a day for one year, or 10 a day for two years. The pack is always counted as 20 cigarettes, whatever size you buy.
Why do pack-years matter?
Pack-years sum up lifetime exposure to tobacco smoke, and the risk of lung cancer and COPD rises with them. Lung cancer screening programmes use pack-years in their criteria; in the United States, the USPSTF recommendation since 2021 covers adults aged 50 to 80 with 20 pack-years or more who smoke now or quit within the past 15 years.
What is the Brinkman index?
Cigarettes per day multiplied by years smoked, without dividing by 20. It is used mainly in Japan and other parts of Asia. 20 a day for 10 years is a Brinkman index of 200 and 10 pack-years.
How do I count cigars, pipes or rolling tobacco?
Pack-years were defined for cigarettes. Roll-ups can be counted as cigarettes. For cigars and pipes there is no single agreed conversion, so tell your doctor what and how much you smoked instead.