Every fall, millions of retirees make the same expensive mistake: they let their Medicare coverage renew on autopilot. They don't open the mail, and they don't check what changed. This year that mistake could cost more than usual. Several important changes take effect January 1, 2027. Here is what's coming, when it's coming, and exactly what to do. YOUR KEY DATES By September 30: If you have a Medicare Advantage or Part D drug plan, your "Annual Notice of Change" (ANOC) should arrive. It's the most important piece of Medicare mail you'll get all year. Don't toss it. October 14: Social Security announces the official 2027 cost-of-living adjustment (COLA). October 15: Medicare Open Enrollment begins. November: Medicare announces the official 2027 Part B premium, deductibles, and income surcharge (IRMAA) brackets. Early December: Social Security mails your personal 2027 benefit notice, showing your new check after Medicare premiums. December 7: Open Enrollment ends. Whatever you have at midnight is what you're living with in 2027. WHAT'S CHANGING (IN PLAIN ENGLISH) 1. Your raise is likely to be one of the bigger ones in years. 2. 3. Current estimates put the 2027 COLA around 3.5% to 3.6%, up from 2.8% this year. On an average retirement check of about $2,086, that's roughly $73 more a month. These are estimates, and the official number comes October 14. 4. Part of that raise goes straight to Medicare. 5. 6. The projected 2027 Part B premium is about $209.50 a month, up from $202.90. If it holds, that takes about $6.60 back out of your raise. The official number comes in November. Watch your net increase, not the headline. 7. Drug costs: the cap goes up, and so does the deductible. 8. 9. The most you'll pay out of pocket for covered Part D drugs rises from $2,100 to $2,400. The maximum deductible rises from $615 to $700. If you take expensive brand-name medications, plan on reaching that cap a little later in the year. 10. Stand-alone drug plan premiums could jump. 11. 12. A temporary federal program that was holding down premiums for stand-alone Part D plans ends after 2026. Plan choices have also been shrinking. The average number of stand-alone plans has dropped from about 30 five years ago to 11 today. Your current plan may cost more, cover less, or not exist next year. 13. Some big-name drugs get lower Medicare prices. 14. 15. Fifteen drugs have negotiated Medicare prices starting in 2027, including Ozempic, Wegovy, Rybelsus, Trelegy, Breo, Januvia's cousin Janumet, Tradjenta, Linzess, Xtandi, and Ibrance. Important: the negotiated price is not the same as your copay. What you actually pay still depends on your plan.