Pack Year Calculator
Pack year calculator works out Pack years and Packs a day from Cigarettes a day, Years smoked at that rate and Cigarettes in a pack. The default figures on this page give pack years of 30.00; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
4 steps
- 20 cigarettes a day / 20 per pack = 1 packs a day.
- 1 x 30 years = 30 pack years.
- Total 30 pack years.
- That reaches the 20 pack-year threshold in the USPSTF lung-cancer screening recommendation.
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
2 sources
What the pack year calculator calculates
Cigarette pack-years: (cigarettes per day / 20) x years smoked, the National Cancer Institute measure of lifetime exposure, with an optional second smoking period. It also reports whether the total reaches the 20 pack-year threshold in the USPSTF lung-cancer screening recommendation, alongside that recommendation’s age and quit-date conditions.
How to use this pack year calculator
Enter Cigarettes a day, Years smoked at that rate, Cigarettes in a pack and Second period: cigarettes a day. Pack years updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Pack years, Packs a day and Pack years, first period.
The method follows National Cancer Institute, NCI Dictionary of Cancer Terms: pack year and US Preventive Services Task Force, Lung Cancer: Screening (2021), Grade B recommendation.
A pack a day for thirty years example
With Cigarettes a day: 20, Years smoked at that rate: 30, the calculator returns Pack years: 30, Packs a day: 1. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Pack years, Packs a day and Pack years, first period. The inputs you can vary are Cigarettes a day, Years smoked at that rate, Cigarettes in a pack, Second period: cigarettes a day, Second period: years and Current age (optional).
Understanding Pack years, Packs a day and Pack years, first period
Pack-years are one input to a screening decision, not a diagnosis. Discuss lung-cancer screening with a clinician.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do you calculate pack-year?
Cigarette pack-years: (cigarettes per day / 20) x years smoked, the National Cancer Institute measure of lifetime exposure, with an optional second smoking period. Open “How this is worked out” beside the result to see each step for your own figures.
What is 1 pack-year of smoking?
Cigarette pack-years: (cigarettes per day / 20) x years smoked, the National Cancer Institute measure of lifetime exposure, with an optional second smoking period. On this page it is computed from Cigarettes a day, Years smoked at that rate and Cigarettes in a pack and shown as Pack years, Packs a day and Pack years, first period.
Is 20 pack-years considered a lot?
Cigarette pack-years: (cigarettes per day / 20) x years smoked, the National Cancer Institute measure of lifetime exposure, with an optional second smoking period. On the figures this page opens with — cigarettes a day 20 and years smoked at that rate 30 — the pack years is 30. Put your own figures in their place and the working updates beside the result.
How many pack-years is considered a heavy smoker?
On the figures this page opens with — cigarettes a day 20 and years smoked at that rate 30 — the pack years is 30. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
What information do I need for the pack year calculator?
You need Cigarettes a day, Years smoked at that rate, Cigarettes in a pack, Second period: cigarettes a day, Second period: years, Current age (optional) and Years since quitting (0 if still smoking). The page opens with default figures that give pack years of 30.00, so you can see the scale before entering your own.
What does this pack year calculator show?
It shows Pack years, Packs a day, Pack years, first period, Pack years, second period, Cigarettes smoked in total, Packs smoked in total, Reaches the 20 pack-year threshold and Meets all three USPSTF conditions, with the working and any warnings for your entries.