A pack-year is a standard way to measure lifetime tobacco exposure. One pack-year equals smoking 20 cigarettes (one pack) per day for one year. The formula is pack-years = (cigarettes per day ÷ 20) × years smoked.

How do I calculate pack-years?

Divide the number of cigarettes smoked per day by 20 to get packs per day, then multiply by the number of years smoked. For example, 10 cigarettes a day for 30 years is (10 ÷ 20) × 30 = 0.5 × 30 = 15 pack-years.

Why do pack-years matter?

Pack-years summarise cumulative smoking exposure in a single number, which clinicians use in lung-cancer risk assessment. Many lung-cancer screening programmes use thresholds such as 20 or 30 pack-years together with age as part of eligibility.

What if my smoking rate changed over time?

Estimate the average for each distinct period (for example 20 a day for 10 years, then 10 a day for 5 years), calculate pack-years for each, and add them together. For a quick estimate, use your overall average cigarettes per day across the whole time.

Is my data sent anywhere?

No. The calculation runs entirely in your browser; your smoking history is never uploaded, stored or logged.

What is the Pack-Years Calculator?

Work out your smoking pack-years — cigarettes per day divided by 20, multiplied by the number of years smoked — a standard measure of lifetime tobacco exposure used in lung-cancer screening. Runs 100% in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Pack-Years Calculator

Name: Pack-Years Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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The Pack-Years Calculator converts how much and how long you have smoked into a single exposure figure used in clinical risk assessment and lung-cancer screening eligibility.

The formula

Pack-years = (cigarettes per day ÷ 20) × years smoked

A pack is counted as 20 cigarettes. So smoking 20 a day for 10 years is exactly 10 pack-years, and smoking 10 a day for 30 years is (10 ÷ 20) × 30 = 15 pack-years.

Worked examples

Cigarettes/day	Years smoked	Pack-years
20	10	10
10	30	15
40	20	40
15	25	18.75

Why pack-years are used

Pack-years compress two variables — intensity and duration — into one number so that very different smoking histories can be compared on the same scale. Lung cancer screening programmes commonly combine a pack-year threshold (often around 20 or 30) with an age range and recency of smoking to decide who is offered a low-dose CT scan.

If your smoking rate changed over the years, split your history into periods, calculate pack-years for each, and add them up for a more accurate total. This tool is for information only and does not replace a clinical assessment.