How do I calculate pack-years?

Pack-years = (cigarettes per day ÷ 20) × years smoked. A pack (20 cigarettes) a day for 20 years = 20 pack-years. The calculator does it from your input.

What is the smoking index?

It’s a measure of accumulated smoking harm. Most often it means pack-years (for lung cancer risk); there’s also the “smoking index” = cigs/day × 12 (for COPD risk). The calculator computes both.

How many pack-years are dangerous?

From 20–30 pack-years a person qualifies for lung cancer screening with low-dose CT. The more pack-years, the higher the risk; a doctor sets the exact approach.

What does a smoking index above 120 mean?

A smoking index (cigs/day × 12) above 120 is considered a COPD risk factor, above 200 a high risk. It’s a reason to check lung function (spirometry) with a doctor.

Does risk drop after quitting?

Yes. Quitting lowers the risk of heart attack, stroke and some cancers at any age. Part of the raised risk persists longer, but quitting is always worthwhile.

Smoking index: pack-years and smoking history

The smoking index shows the accumulated harm from smoking. Enter cigarettes per day and years — the calculator computes pack-years (the key measure for lung cancer risk) and the smoking index (for COPD risk).

Calculate the smoking index

Enter cigarettes per day (and years) — the result appears instantly.

How smoking history is assessed

Pack-years is the cumulative dose for lung cancer risk; the smoking index (cigs/day × 12) is for COPD risk. Thresholds are approximate; a doctor interprets them.

Metric	Assessment
Pack-years 20 or more	Lung cancer screening threshold
Pack-years 30 or more	High risk
Smoking index > 120	COPD risk factor
Smoking index > 200	High COPD risk

What pack-years are

Pack-years = (cigarettes per day ÷ 20) × years smoked. For example, a pack a day (20 cigarettes) for 20 years = 20 pack-years. It’s the standard measure of cumulative tobacco dose.

At 20–30 pack-years or more a person falls into the group for lung cancer screening (low-dose CT). The more pack-years, the higher the risk.

The smoking index and COPD risk

The smoking index = cigarettes per day × 12 (months). A value above 120 is considered a risk factor for chronic obstructive pulmonary disease (COPD), above 200 a high risk.

The two measures complement each other: pack-years target lung cancer, the smoking index targets COPD.

Why calculate it and what to do

Knowing your history in pack-years helps you get screened in time and assess risks with a doctor. But the main takeaway is one: quitting lowers risk at any age and any smoking history.

Within a few years of quitting, the risk of heart attack and some cancers drops noticeably, though part of the raised risk persists longer.

Frequently asked questions

Pack-years = (cigarettes per day ÷ 20) × years smoked. A pack (20 cigarettes) a day for 20 years = 20 pack-years. The calculator does it from your input.
It’s a measure of accumulated smoking harm. Most often it means pack-years (for lung cancer risk); there’s also the “smoking index” = cigs/day × 12 (for COPD risk). The calculator computes both.
From 20–30 pack-years a person qualifies for lung cancer screening with low-dose CT. The more pack-years, the higher the risk; a doctor sets the exact approach.
A smoking index (cigs/day × 12) above 120 is considered a COPD risk factor, above 200 a high risk. It’s a reason to check lung function (spirometry) with a doctor.
Yes. Quitting lowers the risk of heart attack, stroke and some cancers at any age. Part of the raised risk persists longer, but quitting is always worthwhile.

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This calculator is for reference and information only and is not a diagnosis. Screening indications and risk assessment are determined by a doctor.