UNDERSTAND THE NUMBER
Pack-years calculator.
Turn a daily cigarette average and the time you smoked into a pack-year estimate. This describes cigarette quantity over time; it does not measure your health.
YOUR ESTIMATE
pack-years
Enter your numbers, then choose Calculate pack-years.
A quantity estimate only. This is not a diagnosis, a risk score, a screening decision or treatment advice.
How are pack-years calculated?
The National Cancer Institute defines pack-years using packs per day multiplied by years smoked. This calculator uses the standard 20-cigarette pack convention described by CDC.
Pack-years = (cigarettes per day ÷ 20) × years smoked
The 20 in this formula is fixed, even if the packs you buy contain a different number of cigarettes. Enter the number of cigarettes you smoke, rather than your number of purchased packs.
Three ways to read the formula.
| Cigarettes per day | Time smoked | Calculation | Pack-years |
|---|---|---|---|
| 20 | 10 years | (20 ÷ 20) × 10 | 10 |
| 10 | 10 years | (10 ÷ 20) × 10 | 5 |
| 20 | 6 months (0.5 years) | (20 ÷ 20) × 0.5 | 0.5 |
What if the amount changed?
Calculate each period separately and add the results. For example, 20 cigarettes a day for five years gives 5 pack-years. Another ten years at 10 a day gives 5 more. The total is 10 pack-years.
Do not count the same years twice. Time without smoking adds no cigarette pack-years. If your history is uncertain, keep that uncertainty with the estimate rather than treating the result as an exact measurement.
What this result cannot tell you.
Two different smoking histories can produce the same pack-year number. The number alone does not describe your current health or establish a safe amount to smoke. This tool does not calculate cancer probability, decide whether a scan is appropriate or recommend medication.
The formula here is for cigarettes. It does not convert vaping, cigars, pipes or other tobacco products into cigarette equivalents. For questions about your history or personal care, discuss it with a qualified healthcare professional.
Looking for cigarette spending instead?
Pack-years count cigarette quantity, not money. To estimate daily, yearly and five-year spending from your own pack price, use the smoking cost calculator.
Formula sources
These sources explain the quantity calculation. They do not evaluate or endorse iQ. The older CDC report is cited for its definition only, not its historical screening recommendations.
For day-to-day progress after quitting, iQ has a smoke-free timer, craving SOS and estimated savings. Free to start, without creating an account.
