Pack-year calculator
Lung cancer screening is a low-dose CT every year for adults 50 to 80 with a 20 pack-year smoking history who smoke now or quit within the past 15 years (USPSTF grade B, 2021). (USPSTF, 2021) A pack-year is how doctors measure a smoking history. The USPSTF puts it this way: "One pack-year is the equivalent of smoking an average of 20 cigarettes (1 pack) per day for a year." (USPSTF, 2021) Enter what you smoked below. If the amount changed over the years, use one row per period.
Meeting the criteria means the recommendation covers you, not that you have or will get lung cancer. Missing them does not mean you are not at risk. Your doctor can weigh your full history, and the first step for screening is a visit to talk it through.
Pack-year examples
| Smoked per day | For | Pack-years |
|---|---|---|
| 1 pack (20 cigarettes) a day | 20 years | 20 |
| Half a pack (10 a day) | 40 years | 20 |
| Half a pack (10 a day) | 30 years | 15 |
| 2 packs (40 a day) | 10 years | 20 |
| 1 pack a day for 10 years, then half a pack for 10 years | 20 years in all | 15 |
The arithmetic is the same one Medicare uses in its own example: 20 pack-years is "an average of one pack (20 cigarettes) per day for 20 years." (Medicare.gov) A lighter smoker can reach the same total over more years, which is why the number of years matters as much as the daily amount.
The screening criteria the total is checked against
| USPSTF (2021, grade B) | Medicare Part B | |
|---|---|---|
| Age | 50 to 80 | 50 to 77 |
| Smoking history | 20 pack-years or more | 20 pack-years or more |
| Smoking now? | Smoke now or quit within the past 15 years | Smoke now or quit within the last 15 years |
| Symptoms | Like all USPSTF recommendations, for people "without obvious related signs or symptoms" | No signs or symptoms of lung cancer |
| Test and how often | Low-dose CT, every year | Low-dose CT, once a year |
| Before the first scan | A visit with your provider to discuss benefits and risks, and an order |
(USPSTF, 2021) (Medicare.gov) Medicare says you "pay nothing if your doctor or other health care provider accepts assignment." Private plan rules are on preventive screenings covered by insurance.
When screening stops
The USPSTF says to "stop screening once a person has not smoked for 15 years or has a health problem that limits life expectancy or the ability to have lung surgery." (USPSTF, 2021) So if you quit, the clock runs from your quit date: someone who quit at 55 would fall outside the recommendation at 70, even though 70 is inside the age range.
What the task force weighed
The USPSTF names "smoking and older age" as "the 2 most important risk factors for lung cancer," and says risk "decreases with increasing time since quitting." It also lists the harms of screening: "false-positive results and incidental findings that can lead to subsequent testing and treatment, including the anxiety of living with a lung lesion that may be cancer," along with "overdiagnosis of lung cancer and the risks of radiation exposure." (USPSTF, 2021) That balance is the reason for the visit to talk it through before the first scan.
Screening does not replace quitting. If you smoke now, the USPSTF has a separate recommendation on help to stop, which your doctor can go through with you.
Questions people ask
How do you calculate pack-years?
Multiply the packs you smoked per day by the number of years you smoked. One pack is 20 cigarettes, so 1 pack a day for a year is 1 pack-year. If the amount changed over time, work out each period separately and add them up.
How many pack-years do you need for lung cancer screening?
At least 20, under the USPSTF 2021 recommendation and Medicare. You also need to be in the age range (50 to 80 for the USPSTF, 50 to 77 for Medicare) and either smoke now or have quit within the past 15 years.
I quit more than 15 years ago. Should I be screened?
The USPSTF says screening stops "once a person has not smoked for 15 years," so its recommendation no longer covers you. That is not a statement that your risk is zero; if you have symptoms or other concerns, talk to your doctor.
Why did the criteria change from 30 to 20 pack-years?
In 2021 the USPSTF lowered the pack-year threshold from 30 to 20 and the starting age from 55 to 50. Its 2013 recommendation covered adults 55 to 80 with 30 pack-years.
Does Medicare pay for lung cancer screening?
Yes, once a year, for people 50 to 77 with no symptoms, at least 20 pack-years, who smoke now or quit within the last 15 years, with an order from a provider. Before the first scan you need a visit to discuss benefits and risks. You pay nothing if the provider accepts assignment.
Related
- Screenings if you smoke or used to: lung, aortic aneurysm and help to quit on one page
- Lung cancer screening: who, how often and what the test is
- Low-dose CT lung scan: what happens at the scan and what results mean
- Abdominal aortic aneurysm screening, the other screening that depends on smoking history
- Quitting smoking: what works, and the free quitline 1-800-QUIT-NOW
- Build my screening plan: tick "heavy smoking history" to include lung screening