Pack Year Calculator

Created by Hanna Pamuła, PhD and Łucja Zaborowska, MD, PhD candidate
Reviewed by Steven Wooding
Based on research by
Bernaards CM, Twisk JW, Snel J, Van Mechelen W, Kemper HC. Is calculating pack-years retrospectively a valid method to estimate life-time tobacco smoking? A comparison between prospectively calculated pack-years and retrospectively calculated pack-years. Addiction (November 2001)
Last updated: Jun 05, 2023

This pack year calculator finds out how many packs of cigarettes you smoked in your life and provides a pack year value. A pack year is a unit used to measure the amount of tobacco a person has smoked over a long period. It is used, for example by clinicians, as a parameter for eligibility to screening for lung cancer. If you are shocked after seeing the result of your pack year value and cigarettes smoked in a lifetime, check out our other useful tools:

How to calculate the pack years?

To calculate the pack year (PY), multiply the number of packs of cigarettes smoked per day (Packs) by the number of years (Years) the person has smoked.

  • PY = Packs × Years


  • PY = (Cigarettes per day/Pack size) × Years, if your pack size is different than standard 20 cigarettes.

If you want to know how many packs (PL) or cigarettes (CL) you already smoked in your life, use the formula:

  • PL = Cigarettes per day × 365.24 × Years
  • CL = (Cigarettes per day/Pack_size) × 365.24 × Years

Example of pack year calculation

One pack year is equivalent to smoking 20 cigarettes a day for one year (1 pack × 1 year). If you are smoking ten cigarettes daily for two years (0.5 pack × 2 years), or two cigarettes per day in your ten years smoking history (0.1 pack × 10 years), it still gives us one smoking pack year.

However, it is still debatable if pack years are good enough for assessing the risk of lung cancer. Some researchers claim that more prolonged exposure to smoke (e.g., 40 years, a half pack per day) poses a higher risk than shorter periods (10 years with two packs per day) even though the number of pack years is the same in both cases.

Advanced mode information

In the advanced mode of the pack year calculator, you can change the pack size, if your packs differ from the standard ones. Also, you can display the packs, and cigarettes smoked in a lifetime - these values usually speak more to our imagination than abstract smoking pack years.


How do I calculate pack years smoking 30 years half of a pack per day?

This is equivalent to 15 pack years.

To calculate it:

  1. Multiply the smoking years by the number of packs smoked daily.
  2. In our case, we multiply
    0.5 pack per day × 30 years = 15 pack years.

What is a 20 pack years smoking history?

A 20 pack years of smoking history means smoking one pack of cigarettes per day for 20 years, smoking two packs for 10 years, or any other pack-year combination that multiplied gives twenty.

Currently, 20 pack years is a critical cutoff. According to the US Preventive Services Task Force, together with age (50-80), 20 pack years is an indication for lung cancer screening.

How many pack years is significant?

No strict rules tell us that some number of cigarettes is significant. The more, the worse, and every cigarette deteriorates your health. However, it is recommended that you screen for lung cancer if you're 50-80 and have 20 pack years of smoking history.

What is a pack year?

A pack year is the equivalent of smoking one standard pack of cigarettes (20 cigarettes) per day for the whole year. Calculating pack years describes how many cigarettes you've smoked in your lifetime.
More pack years correlate with higher lung disease risk.

Hanna Pamuła, PhD and Łucja Zaborowska, MD, PhD candidate
/ day
I have been smoking for...
Pack years
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