5 Medicare Enrollment Mistakes That Cost People Thousands

In my years helping clients navigate Medicare, I've seen the same mistakes come up again and again. The painful part is that most of them are completely avoidable — if you know the rules before you hit the enrollment windows. Here are the five that cost people the most.

Mistake 1: Assuming You're Auto-Enrolled in Everything

If you're already receiving Social Security benefits when you turn 65, you'll be automatically enrolled in Medicare Parts A and B. But if you're not yet taking Social Security — which is true for many people who delay benefits — you have to actively enroll.

The Initial Enrollment Period (IEP) runs for 7 months: the 3 months before your 65th birthday month, your birthday month itself, and the 3 months after. Miss this window without a qualifying Special Enrollment Period, and you face permanent penalties.

Mistake 2: Thinking Employer Coverage Protects You Indefinitely

This is one of the most common and expensive misconceptions. If you're still working at 65 with employer coverage, you may qualify for a Special Enrollment Period to delay Medicare without penalty — but only under specific conditions:

• The coverage must be through your own current employment (not COBRA, retiree coverage, or a spouse's employer)
• The employer must have 20+ employees

If your employer has fewer than 20 employees, Medicare becomes your primary coverage at 65 whether you sign up or not. If you don't enroll, your claims may be denied.

Mistake 3: Missing the Part D Window

Part D (prescription drug coverage) has its own enrollment rules. If you don't sign up when you're first eligible and you go 63+ days without creditable drug coverage, you'll owe a late enrollment penalty when you do eventually sign up.

The penalty is calculated as 1% of the national base beneficiary premium for every month you went without coverage — and it's added to your Part D premium permanently.

Mistake 4: Treating Open Enrollment as Your Only Chance to Change Plans

Medicare's Annual Enrollment Period (October 15 – December 7) gets a lot of attention, but it's not the only time you can make changes. There are several other enrollment periods people don't know about:

• Medicare Advantage Open Enrollment (January 1 – March 31): Switch MA plans or go back to Original Medicare
• Special Enrollment Periods triggered by life events: losing employer coverage, moving out of a plan's service area, qualifying for Extra Help
• Medigap Guarantee Issue rights: specific windows when insurers must accept you regardless of health

Many people think if they missed October 15th, they're stuck for a year. They're not always.

Mistake 5: Picking a Plan Based on Premium Alone

The lowest-premium Medicare Advantage plan in your area might look great until you check the network, the drug formulary, and the maximum out-of-pocket limit.

We've seen clients choose a $0-premium Advantage plan and then spend $6,000+ in a single year because their specialist was out of network or their primary medication wasn't covered at the formulary tier they expected.

Always model the total cost of the plan against your specific medications, doctors, and anticipated healthcare use — not just the monthly premium.

Debbie Denesha

Medicare Specialist · Denesha Insurance Agency

Debbie works alongside Terry, helping clients navigate life insurance and benefits decisions with patience, clarity, and zero pressure.