IMPORTANCE The closure of the Medicare Part D coverage gap from 2010 to 2019 was intended to help decrease out-of-pocket costs for beneficiaries, especially those taking high-cost drugs. However, yearly increases in list prices and the introduction of newer and more expensive drugs may have limited savings for beneficiaries. OBJECTIVE To assess the association of closure in the Medicare Part D coverage gap with projected annual out-of-pocket costs from 2010 through 2019 for rheumatoid arthritis (RA) biologics. DESIGN, SETTING, AND PARTICIPANTS This cross-sectional analysis used data from the Medicare Formulary and Pricing Files for the first quarter (January 1 to March 31) in each calendar year from 2010 to 2019 for 17 RA biologic drug and strength combinations. EXPOSURES Medicare Part D plan design and drug price by year. MAIN OUTCOMES AND MEASURES Expected annual out-of-pocket costs for 1 year of treatment.RESULTS Among the 17 drug and strength combinations assessed, list prices increased each year for every product, with a mean increase of 160% for the 6 drugs available during the entire study period.