Last updated: October 9, 2026
A pack-year history (often written “PY” or “pk-yr hx”) is your total lifetime cigarette exposure. One pack-year is 20 cigarettes a day for one year. Because most people smoke different amounts at different ages, the accurate way is to calculate each period separately and add them up, leaving out years when you did not smoke.
Example below: 10 a day as a young adult, a pack a day in your 30s and 40s, then cutting down. Edit the rows to match your own history.
| Period | Cigarettes/day | Years | Pack-years | Remove |
|---|
Total: 0 pack-years over 0 smoking years
| Age | Cigarettes/day | Years | Pack-years |
|---|---|---|---|
| 17–25 | 10 | 8 | 4 |
| 25–36 | 30 | 11 | 16.5 |
| 36–40 | quit | – | 0 |
| 40–62 | 15 | 22 | 16.5 |
| Total | 41 smoking years | 37 pack-years |
Using “a pack a day since 17” would have given 45 pack-years; ignoring the heavy years would have given far less. Period-by-period is what clinicians and screening programmes expect.
| Note | Meaning |
|---|---|
| “30 PY” / “30 pk-yr hx” | 30 pack-year smoking history |
| “Current smoker, 1 ppd × 25 yrs = 25 PY” | one pack per day for 25 years |
| “Former smoker, 40 PY, quit 2018” | 40 pack-years, stopped in 2018 |
| “Never smoker” | fewer than 100 cigarettes in a lifetime (common survey definition) |
“ppd” means packs per day; “hx” means history. For screening decisions, clinicians need three things: total pack-years, number of smoking years, and the date you quit (if you did).
It is your total cigarette exposure expressed in pack-years: cigarettes per day divided by 20, multiplied by the years you smoked, added up across every period of your life.
Calculate each period separately (cigarettes per day ÷ 20 × years) and add the results. Leave out years when you did not smoke. The calculator above does this for you.
It means total exposure equal to one pack a day for 30 years, for example 20 cigarettes daily for 30 years or 30 cigarettes daily for 20 years. See 30 pack years.
Common abbreviations are PY, pk-yr or pack-yr, often with hx for history, for example “30 pk-yr hx”.
No. Pack-years record past exposure and stay the same. Your lung cancer risk does fall the longer you stay quit: pack years after quitting.
Medical disclaimer: This page is for information only and is not medical advice. Talk to a qualified healthcare professional about your own situation.