Pack-Years Calculator — Cigarette Smoking Exposure

The Pack-Years calculator quantifies cumulative tobacco smoking exposure in a standardized unit: one pack-year equals smoking one pack (20 cigarettes) per day for one year. Formula: Pack-Years = (Packs smoked per day) × (Years smoked) = (Cigarettes per day / 20) × Years smoked. Pack-year history is a critical clinical parameter used for: lung cancer screening eligibility (low-dose CT; USPSTF 2021 criteria require ≥ 20 pack-years), COPD severity assessment and spirometric prediction, perioperative risk stratification, insurance mortality risk scoring, and epidemiologic research. Pack-years provide a single quantitative summary of tobacco exposure that captures both duration and intensity of smoking.