Supplemental Medicare Insurance: The Gap Benefits Nobody Knows They Need

The Medicare summary notice arrived on a Tuesday. $4,600 in charges that Medicare had not covered. I was 68 years old, on a fixed income, and facing a gap in coverage I had not understood when I signed up for Medicare. The 20% that Medicare does not cover had just cost me more than my monthly Social Security check.

That was when I learned why supplemental Medicare insurance exists — and why most people wait too long to buy it.

Understanding the Medicare Gap

Original Medicare has a significant gap that surprises most new beneficiaries: it only covers 80% of Medicare-approved amounts for Part B services (doctor visits, outpatient care, preventive services). The remaining 20% is your responsibility, with no annual cap on out-of-pocket spending.

For a senior with multiple chronic conditions, that 20% can add up to $10,000 to $30,000 per year in medical costs — not counting prescription drugs, which have their own separate coverage system (Part D).

Dr. James Morrison, a Medicare specialist in Cleveland who has helped thousands of seniors navigate their coverage options, told me the 20% gap is what surprises most new Medicare beneficiaries. They assume Medicare covers their medical costs. They do not realize there is a significant gap that can expose them to substantial financial risk.

What Medigap Actually Covers

Medigap (supplemental Medicare insurance) is specifically designed to fill the gaps in original Medicare. There are 10 standardized plans (A through N), each covering different combinations of:

Part A hospital deductible ($1,676 per benefit period in 2026)

Part B deductible ($257 per year)

Part B copayments (20% of Medicare-approved amounts)

Part B excess charges (the difference between what a doctor charges and what Medicare approves)

Skilled nursing facility coinsurance

Hospice care coinsurance

Foreign travel emergency coverage

With a comprehensive Medigap Plan G, your out-of-pocket costs for Medicare-covered services can be reduced to minimal amounts — you pay the Part B deductible ($257) and nothing else for the rest of the year.

The Critical Enrollment Window

Medigap has a one-time 6-month enrollment window that starts when you turn 65 and enroll in Medicare Part B. During this period, insurance companies cannot deny you coverage or charge you more based on pre-existing conditions.

After this window closes, getting Medigap coverage can be much harder. If you have health conditions, insurance companies can decline you or charge premiums that are unaffordable. If you missed the window, you may be stuck with Medicare original coverage and no way to add supplemental coverage.

My neighbor was diagnosed with diabetes at 64. She missed her Medigap enrollment window because she was dealing with the diabetes diagnosis. When she tried to buy supplemental coverage at 67, every insurance company declined her because of her diabetes and related complications. She has been paying the 20% Medicare gap for five years now and expects to pay it for the rest of her life.

The Price of Waiting

The median Medigap Plan G premium for a 65-year-old is approximately $180 per month. For a 75-year-old, the median premium is approximately $280 per month. The same coverage costs $100 more per month just because you waited 10 years to buy it — and that assumes you can still get coverage at 75.

If you wait until you have health problems to buy supplemental coverage, you may not be able to get it at any price. The insurance companies know that people with health conditions are more likely to use their coverage, so they decline or price out anyone with significant health issues.

What I Did After Learning This Lesson

After my first year with Medicare and $4,600 in uncovered costs, I immediately enrolled in a Medigap Plan G policy. My monthly premium is $195, which is more than I was paying before — but now my out-of-pocket costs for Medicare-covered services are limited to $257 per year (the Part B deductible).

In the three years since I bought the Medigap policy, I have had two hospitalizations, multiple specialist visits, and a surgical procedure. My total out-of-pocket costs (premiums plus deductibles and copays) have been approximately $8,500. Without Medigap, those same services would have cost me over $22,000 out of pocket.

The lesson is simple: the time to buy supplemental Medicare insurance is when you first qualify, during your open enrollment window, before you have any health conditions that could make coverage unavailable or unaffordable.