The Patient Protection and Affordable Care Act requires that individuals have health insurance or pay a penalty. Individuals are exempt from paying this penalty if the after-subsidy cost of the least-expensive plan available to them is greater than 8% of their income. For this study, premium data for all health plans offered on the state and federal health insurance marketplaces were collected; the after-subsidy cost of premiums for the least-expensive bronze plan for every county in the United States was calculated; and variations in premium affordability by age, income, and geographic area were assessed. Results indicated that-although marketplace subsidies ensure affordable health insurance for most persons in the United States-many individuals with incomes just above the subsidy threshold will lack affordable coverage and will be exempt from the mandate. Furthermore, young individuals with low incomes often pay as much as or more than older individuals for bronze plans. If substantial numbers of younger, healthier adults choose to remain uninsured because of cost, health insurance premiums across all ages may increase over time.