Smoking Pack-Years
One pack-year is a pack a day (20 cigarettes) for one year. Divide daily cigarettes by 20 for packs and multiply by the years. Half a pack for forty years and two packs for ten both come to 20 pack-years.
Your numbers
Pack-years
15pack-yr
Count
109,500
Percentage
75%
What it means
15 pack-years. The figure does not fall after quitting, but the risk does over time.
Formula
Pack-years = Cigarettes a day ÷ 20 × Years smoking
For the same total, how recently you smoked weighs more heavily on risk. Pack-years is only one axis of it.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Cigarettes a dayCigarettes smoked a day; a pack is twenty. | 15 | 0 ~ 100 |
| Years smoking (yr)How many years you smoked at that rate. | 20 | 0 ~ 80 |
Step by step
Quick reference table
Results when only Cigarettes a day changes and everything else stays put.
| Cigarettes a day | Pack-years (pack-yr) | Count | Percentage (%) |
|---|---|---|---|
| 7.5 | 7.5 | 54,750 | 38 |
| 11.3 | 11.3 | 82,490 | 57 |
| 15 | 15 | 109,500 | 75 |
| 22.5 | 22.5 | 164,250 | 113 |
| 30 | 30 | 219,000 | 150 |
What each result means
| Result | At default values |
|---|---|
| Pack-years (pack-yr)Cumulative exposure, where one is a pack a day for a year. | 15 |
| CountA plain count of items; it often ends up as the denominator. | 109,500 |
| Percentage (%)A share expressed out of 100. | 75 |
Common mistakes
For the same total, how recently you smoked weighs more heavily on risk. Pack-years is only one axis of it.
Glossary
- Cigarettes a day
- Cigarettes smoked a day; a pack is twenty.
- Years smoking
- How many years you smoked at that rate.
- Pack-years
- Cumulative exposure, where one is a pack a day for a year.
- Count
- A plain count of items; it often ends up as the denominator.
- Percentage
- A share expressed out of 100.
Frequently asked questions
Q. How is Smoking Pack-Years calculated?
Pack-years = Cigarettes a day ÷ 20 × Years smoking — One pack-year is a pack a day (20 cigarettes) for one year. Divide daily cigarettes by 20 for packs and multiply by the years. Half a pack for forty years and two packs for ten both come to 20 pack-years.
Q. Can you walk through an example?
With Cigarettes a day 15, Years smoking 20yr, the answer is Pack-years 15pack-yr.
Q. What do I need to enter?
Enter Cigarettes a day, Years smoking. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Cigarettes a day moves the answer to Cigarettes a day 7.5 → Pack-years (pack-yr) 7.5 and Cigarettes a day 30 → Pack-years (pack-yr) 30. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
For the same total, how recently you smoked weighs more heavily on risk. Pack-years is only one axis of it.
Related calculators
These calculators help you understand health figures; they do not replace diagnosis or prescription. See a clinician if you have symptoms.