About the Lung Cancer Risk Calculator for Smokers
This tool calculates two well-established, transparent numbers for people with a smoking history: pack-years, the standard clinical measure of cumulative cigarette exposure, and whether that history meets the 2021 U.S. Preventive Services Task Force (USPSTF) criteria for annual low-dose CT lung cancer screening. It does not estimate a personal probability of developing lung cancer - it checks eligibility against a published screening guideline.
How pack-years are calculated
Pack-years use a simple, widely adopted formula: divide the average number of cigarettes smoked per day by 20 (the number of cigarettes in a standard pack), then multiply by the number of years smoked. Smoking one pack (20 cigarettes) a day for one year equals one pack-year. Smoking two packs a day for 15 years equals 30 pack-years, and half a pack a day for 40 years also equals 30 pack-years - the formula treats total cumulative exposure as the driver, not the daily rate alone.
The USPSTF 2021 screening criteria
The USPSTF recommends annual low-dose CT screening for adults who meet all three conditions: age 50 to 80 years, at least a 20 pack-year smoking history, and either currently smoking or having quit within the past 15 years. The guideline also notes that screening should generally stop once someone has not smoked for 15 years or has a health problem that substantially limits life expectancy or the ability to have curative lung surgery. This calculator checks the first three conditions against your inputs.
What this calculator does not do
It does not include other established lung cancer risk factors, such as family history, radon exposure, occupational exposures like asbestos, or prior chest radiation, that more detailed clinical risk models (for example PLCOm2012 or the Bach model) incorporate. It also does not diagnose lung cancer or any other condition - it is strictly a pack-year and guideline-eligibility calculation.
When to consult a professional
Whether or not you meet the USPSTF criteria, discuss your smoking history and any screening decision with a healthcare provider. Clinicians may recommend screening for people outside these criteria based on individual risk factors, and shared decision-making is part of the standard screening process.