Working Past 65 or on COBRA: When You Must Sign Up for Medicare Part B, and What a Late Penalty Costs
If you or your spouse are still working for an employer with 20+ employees and covered through that job, you can delay Part B and sign up within 8 months after the job or coverage ends. COBRA and retiree coverage don't count, so the 8 months start when the job ends. Miss it and Part B costs 10% more per full 12 months, for life.
Read article