Calculate your pack-years in a minute
A pack year calculator turns a smoking history into a single number doctors use to describe tobacco exposure. One pack-year means smoking one pack of 20 cigarettes a day for one year. This tool multiplies packs per day by years smoked, lets you add up to three periods (for example when you smoked more heavily, or cut down), and handles cigarettes, bidis and cigars.
Doctors ask for pack-years when they assess lung disease, heart risk and eligibility for lung cancer screening. Everything is calculated in your browser, nothing is stored or sent anywhere, and the result is an estimate of exposure, not a medical assessment.
How to use the Pack-Year Calculator
- Enter how many you smoke or smoked per day and for how many years in the first row.
- Choose what you smoke: cigarettes, bidis or cigars. If your habit changed, fill in period 2 and period 3.
- Open Sticks per pack-equivalent if your packs are not 20 sticks, or to set a conversion for bidis and cigars.
- Read the total pack-years, the average packs per day and the breakdown table for each period.
- Take the number to your doctor or screening service; do not use it to diagnose yourself.
Pack-Year Calculator features
Multiple periods
Add up to three stretches of smoking, each with its own daily amount, product and number of years.
Bidis and cigars
Pick a product and set how many sticks count as one pack, because there is no official conversion.
Formula shown
Every row shows packs per day and pack-years, so you can check the sum by hand.
Screening note
A plain note about the 20 pack-year threshold used in many lung cancer screening guidelines.
Quit help
Quitline numbers for England, the US and India sit under the result.
The pack-year formula
The National Cancer Institute defines a pack-year as the number of packs of cigarettes smoked per day multiplied by the number of years smoked. The formula is pack-years = (cigarettes per day ÷ 20) × years smoked.
Worked example: 15 cigarettes a day for 20 years is 0.75 packs × 20 = 15 pack-years. Add 10 a day for another 5 years (0.5 × 5 = 2.5) and the total is 17.5 pack-years.
| Smoking pattern | Pack-years |
|---|---|
| 10 a day for 10 years | 5.0 |
| 20 a day for 20 years | 20.0 |
| 30 a day for 25 years | 37.5 |
| 5 a day for 40 years | 10.0 |
Why doctors ask: lung cancer screening
The US Preventive Services Task Force (2021) recommends yearly low-dose CT screening for adults aged 50 to 80 who have at least 20 pack-years and currently smoke or quit within the past 15 years. Other countries set their own rules: England is rolling out a targeted lung screening programme for people who have ever smoked in an older age band, so check the NHS website for current eligibility.
Pack-years are also used when assessing COPD and cardiovascular risk. The ASCVD risk calculator asks only whether you currently smoke, so pack-years complement it rather than replace it.
Bidis, cigars and other products
Pack-years were designed for manufactured cigarettes. Bidis, cigars, pipes and hookah have no agreed conversion, because the amount of tobacco and the way people inhale vary. This tool therefore lets you set the number of sticks that count as one pack-equivalent (20 by default). Treat those results as a rough, consistent measure, and tell your doctor what you actually smoked.
- Roll-your-own: estimate how many roll-ups you make from a pouch and enter the daily count as cigarettes.
- Vaping: pack-years do not apply to e-cigarettes.
- Quit years: enter only the years you actually smoked; the clock stops when you quit.
Stopping smoking
It is never too late to stop, and lung health keeps improving after you do. In England the NHS Smokefree service is on 0300 123 1044; in the US, 1-800-QUIT-NOW (1-800-784-8669) connects you to your state quitline; in India, the National Tobacco Quitline is 1800-11-2356. Numbers change, so confirm the one for your region. Related tools: alcohol unit calculator and BMI calculator.
Pack-Year Calculator FAQ
How do you calculate pack years?
Divide the cigarettes you smoke per day by 20 to get packs per day, then multiply by the number of years you smoked. Twenty a day for 10 years is 10 pack-years; 10 a day for 10 years is 5.
What is the pack year formula?
Pack-years = packs per day × years smoked, where one pack is 20 cigarettes. For several periods, work out each one and add the results.
How many pack years is a lot?
There is no single cut-off. Twenty pack-years is a common threshold in lung cancer screening guidelines, and risks keep rising with more exposure. Your doctor decides what matters for you.
Does the NHS use pack years?
Clinicians in the NHS and elsewhere record smoking history in pack-years, and screening and COPD assessments use it. For your own eligibility, check the NHS site or ask your GP, because rules depend on age and area.
Do bidis and cigars count as pack years?
There is no official conversion. Set how many bidis or cigars you treat as one pack-equivalent (20 by default) and use the figure only as a rough guide.
Do I count years after I stopped?
No. Count only the years you smoked. If you quit and restarted, use separate periods and leave the gap out.