Pack Years Calculator
Calculate pack-years — the standard clinical measure of lifetime smoking exposure that screening guidelines are written around.
Pack-years
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Packs per day —
Screening note —
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How it works
Pack-years = (cigarettes per day ÷ 20) × years smokedFrequently Asked Questions
What is a pack-year?
Smoking one pack (20 cigarettes) a day for one year. Half a pack a day for 20 years and two packs a day for 5 years are both 10 pack-years — it measures total exposure.
Why do pack-years matter?
They drive screening eligibility: US guidelines recommend annual low-dose CT lung screening for adults 50–80 with a 20+ pack-year history who smoke or quit within 15 years.
Does quitting reset my pack-years?
The number is lifetime and doesn't decrease, but risk does fall steadily after quitting — substantially within 5–10 years. Pack-years measure the past; quitting changes the future.