Medicare Supplement Plans Explained: Agent Guide

TL;DR: Medicare supplement plans (also called Medigap) help cover the out-of-pocket costs that original Medicare leaves behind — things like copays, coinsurance, and deductibles. For insurance agents, understanding how each plan type works is the foundation of a productive Medicare book of business.

If you sell Medicare products, you already know the conversation always starts the same way. A prospect turns 65, they’ve just enrolled in Medicare Parts A and B, and now they’re staring at an explanation of benefits wondering why they owe anything at all. That’s your opening.

Medicare supplement plans exist to fill those gaps. Your job is to explain them clearly, match the right plan to the right client, and do it fast enough to earn the trust of someone who’s been bombarded with mailers and TV ads for months. This guide breaks down what you need to know — the plan types, how they’re sold, and how to build a system that supports that whole workflow at scale.

What Are Medicare Supplement Plans?

Medicare supplement plans — officially called Medigap — are private health insurance policies that work alongside original Medicare (Parts A and B). They don’t replace Medicare. They fill in the cost-sharing gaps that Medicare leaves behind.

Original Medicare covers roughly 80% of approved medical costs after the beneficiary meets their Part B deductible. The remaining 20% — plus hospital deductibles, coinsurance, and excess charges — can add up fast. Medicare supplement plans cover some or all of those remaining costs depending on the plan the client selects.

Plans are standardized by the federal government and sold through private insurers. That means Plan G from Carrier A covers exactly the same benefits as Plan G from Carrier B. The only difference is the premium. This is critical for agents to communicate: clients are not comparing apples to oranges when they shop by price among the same plan letter.

The Standardized Plan Letters

The Centers for Medicare & Medicaid Services (CMS) standardizes Medigap into lettered plan types. As of 2024, the available plans for new enrollees are: A, B, D, G, G-HD (high deductible), K, L, M, and N. Plans C and F are still available to beneficiaries who were eligible for Medicare before January 1, 2020, but new enrollees cannot purchase them (CMS Medicare Supplement Insurance).

Here’s a practical breakdown of the plans your clients will most commonly ask about:

Plan G is the most popular option for new enrollees. It covers everything Plan F used to cover, except the Part B deductible (which is $240 in 2024). Once the client pays that deductible, Plan G covers 100% of their remaining Medicare-approved costs. For most healthy enrollees, Plan G offers the strongest protection.

Plan N is a lower-premium alternative to Plan G. The trade-off: clients pay copays of up to $20 for office visits and up to $50 for emergency room visits that don’t result in an inpatient admission. Plan N does not cover Part B excess charges, which matters if your client sees doctors who don’t accept Medicare assignment.

Plan K and Plan L are cost-sharing plans. They cover a percentage of costs rather than 100%, which keeps premiums low but leaves the client with meaningful out-of-pocket exposure. These tend to appeal to healthier clients who want a safety net at a lower monthly cost.

Plan G-HD (High Deductible) has a high annual deductible (set at $2,800 in 2024) before coverage kicks in. After that deductible, it covers what standard Plan G covers. Premiums are significantly lower — often half or less of standard Plan G. Good fit for clients with low healthcare utilization who prefer predictable premium costs.

How Medicare Supplement Plans Are Priced

Since benefits are standardized, the variable is the premium. Insurers use three rating methods, and understanding these helps you explain long-term cost trajectory to clients:

Community-rated plans charge the same premium to all enrollees regardless of age. Rates may increase with inflation, but not because the policyholder gets older.

Issue-age-rated plans set the premium based on the age when the policy is purchased and do not increase due to aging. Younger buyers lock in a lower base rate.

Attained-age-rated plans start low and increase as the policyholder ages. These look attractive at enrollment but often become the most expensive option over a 10-20 year horizon.

Many clients don’t know these distinctions exist. Walking them through this builds trust and differentiates you from the agent who just sends a quote sheet.

For current national premium data and carrier comparisons by state, the NAIC Medigap Shopper’s Guide is a reliable, bookmarkable reference.

Enrollment Windows and Underwriting Rules

The most important window in Medigap sales is the Open Enrollment Period (OEP). This is the six-month period that begins the first month a beneficiary is both 65 or older and enrolled in Medicare Part B. During this window, insurers cannot deny coverage or charge higher premiums based on health history. It’s guaranteed issue.

Outside of this window, most states allow carriers to use medical underwriting to approve or deny applicants, or to exclude pre-existing conditions for a period of time. This means the OEP window matters enormously — and clients who miss it may face limited options or higher costs.

There are also Guaranteed Issue Rights (GIRs) that apply in specific situations — like losing employer coverage, moving out of a plan’s service area, or a plan being discontinued. These rights restore the ability to enroll without underwriting. Knowing GIR scenarios cold makes you a more valuable advisor.

For agents working the Medicare vertical, response time to new inquiries is one of the biggest variables in whether you close. Prospects turning 65 are actively researching — they don’t wait. Staying on top of lead response time best practices for insurance agents can directly affect your close rate in this market.

Medicare Supplement Plans vs. Medicare Advantage

This is the most common comparison clients bring up — and one of the most important conversations to get right.

Medicare Advantage (Part C) replaces original Medicare with a private insurance plan, often with lower premiums (sometimes $0) and added benefits like dental or vision. However, Advantage plans typically operate within a network and require prior authorizations.

Medicare supplement plans keep the client on original Medicare, with nationwide provider access and no prior authorization requirements in most cases. The trade-off is a higher monthly premium.

Neither is universally better. The right answer depends on the client’s health status, preferred doctors, geographic location, and financial situation. Your role is to present both options honestly and document the conversation thoroughly.

This distinction also matters for how you organize your book of business. Clients in Medicare Advantage and clients with Medigap have completely different renewal cycles, underwriting histories, and annual review triggers. Managing both in the same workflow without proper tracking creates gaps — and gaps mean lapses.

Building a Medicare Supplement Sales System That Scales

Here’s where most agents lose time: they understand the product, but they don’t have a repeatable process to move leads through the pipeline without dropping the ball.

The Medicare market has specific timing pressures. Turning-65 leads have a hard eligibility window. Clients approaching their OEP need outreach at the right moment — not three weeks late when they’ve already enrolled in something else. Annual reviews need to happen every 12 months so you can reassess whether the client’s current plan still makes sense as carriers adjust rates.

For agents who want to know more about the systems side of the business, why insurance agents struggle to scale covers the operational gaps that tend to hold growth back.

Onyx CRM’s Medicare Stack is built around exactly these workflows. When a Medicare lead comes in, automated pipelines trigger immediate follow-up, push the lead through qualification stages, and — when the prospect is ready — the AI booking agent schedules the appointment without back-and-forth. Annual review reminders run automatically so your existing clients hear from you before a competitor does. It’s the kind of system that makes the Medicare vertical actually workable at volume — not just in theory.

See how the platform handles lead tracking at Medicare Agent Lead Management: Systems That Work.

Annual Reviews: The Retention Strategy Agents Ignore

Most agents focus on acquisition and treat annual reviews as a nice-to-have. This is a mistake.

In the Medicare supplement market, carriers adjust premiums every year — sometimes significantly. A client who is happy in year one may be sitting on a plan that’s 20% more expensive in year four from a carrier that has consistently increased rates. If you’re not the one reviewing that with them, someone else will.

Annual reviews are also the right time to assess whether a client’s health status allows them to switch carriers for a lower premium on the same plan letter. In most states, switching requires underwriting outside of the OEP. A client in good health who has been with an aggressive rate-increasing carrier for three years is often a switcher — if you help them see the math.

Building a consistent annual review schedule is one of the highest-ROI activities in Medicare sales. It protects your book and generates referrals. For more on building retention processes that work, Insurance Client Retention: Keep Your Best Customers is a useful read.

FAQ: Medicare Supplement Plans

What’s the difference between Medicare supplement plans and Medicare Advantage?

Medicare supplement plans (Medigap) work alongside original Medicare (Parts A and B) to cover the out-of-pocket costs Medicare doesn’t pay — like coinsurance, copays, and deductibles. The client stays on original Medicare and keeps access to any provider who accepts Medicare, nationwide.

Medicare Advantage (Part C) replaces original Medicare with a private insurance plan. These plans often have lower premiums and may include extra benefits like dental or vision, but they typically operate within a provider network and may require prior authorizations for certain services.

The right choice depends on the individual’s health, finances, and how much flexibility they want in choosing providers. Agents should present both options clearly and document the discussion. For most clients in good health who travel frequently or see specialists regularly, Medigap’s nationwide access is a significant advantage. For budget-conscious clients in good health with local provider preferences, Advantage plans deserve a fair look.

Which Medicare supplement plan is most popular?

Plan G is the most widely purchased Medicare supplement plan for new enrollees as of 2024. It covers virtually all out-of-pocket Medicare costs except the Part B deductible, which in 2024 is $240. After the client pays that deductible, Plan G covers 100% of Medicare-approved costs for the rest of the year — no copays, no coinsurance.

Plan G replaced Plan F as the benchmark plan after the Medigap Modernization Act eliminated Plan F and Plan C for new Medicare enrollees starting January 1, 2020. Agents should note that Plan F is still valid for beneficiaries who became Medicare-eligible before 2020. For most new enrollees, Plan G represents the best balance of coverage and premium cost.

Can a client be denied a Medicare supplement plan?

Yes — outside of the six-month Open Enrollment Period (OEP) that starts when a beneficiary is 65 and enrolled in Part B, insurance carriers in most states can use medical underwriting to deny coverage or charge higher premiums. During the OEP, enrollment is guaranteed issue — no carrier can turn down an eligible applicant based on health history.

There are specific Guaranteed Issue Rights (GIRs) that may restore access to Medigap without underwriting in certain situations, such as losing employer-sponsored coverage, a plan being discontinued, or moving out of a plan’s service area. Agents should know these scenarios in detail, because properly identifying a GIR situation can mean the difference between a client getting coverage or not.

Are Medicare supplement plans available in all states?

Medigap plans are available in all 50 states, but the rules can vary. Massachusetts, Minnesota, and Wisconsin standardize their plans differently than the rest of the country — using their own plan structures rather than the lettered CMS model. Agents licensed in those states should familiarize themselves with state-specific plan designs.

In all other states, the CMS standardized letter plans apply and benefit sets are identical across carriers for the same plan letter. Premium differences between carriers for the same plan letter are entirely driven by the insurer’s pricing, rating method, and underwriting history. Shopping by premium and rating method is the key variable when helping clients compare options.

How do Medicare supplement premiums change over time?

Premiums for Medicare supplement plans can and do increase over time, but the mechanism depends on the carrier’s rating method. Community-rated plans charge the same premium regardless of age and adjust for inflation and claims history. Issue-age-rated plans lock in a base rate at enrollment and don’t increase due to aging. Attained-age-rated plans start low and increase as the policyholder gets older — these often end up being the most expensive over a 15-20 year hold period.

Community-rated and issue-age-rated plans tend to offer more premium stability for clients who plan to keep coverage long-term. Agents who help clients understand rating methods — not just the current monthly premium — provide significantly more value than those who only share a quote sheet.

Ready to Build a Medicare Book of Business?

Medicare supplement plans are a durable product in a growing market. Every year, about 10,000 Americans turn 65 (Pew Research, 2010). That pipeline doesn’t slow down.

The agents who win long-term are not necessarily the ones with the best product knowledge — they’re the ones with the best systems. They respond first, follow up consistently, schedule annual reviews automatically, and don’t let leads expire in an unorganized inbox.

Onyx CRM’s Medicare Stack supports the full workflow: lead capture, automated nurture, AI appointment booking, and annual review reminders — all in one platform purpose-built for insurance agents. Plans start at $99/month. See pricing at onyx-crm.com/pricing.