What to Know Before You Enroll in Medicare

The smartest Medicare strategy has far less to do with your birthday and far more to do with your employment status, existing health coverage, prescription drug needs, travel habits, income level, and long-term retirement income structure. Two people turning 65 in the same month can have completely different correct enrollment decisions depending on whether they are still working, what their employer’s plan covers, how many employees their employer has, and whether their income will trigger IRMAA surcharges that permanently change the cost of Part B and Part D coverage. The standard Part B premium is $202.90 per month — but high-income beneficiaries pay up to $689.90 per month because of IRMAA surcharges based on income from two years prior. The financial implications of these decisions, compounded over a 20-30 year retirement, are significant. A single wrong turn on enrollment timing can cost thousands of dollars in avoidable penalties and hundreds of dollars per month in unnecessary premiums.

At Diversified Insurance Brokers, our Medicare specialist Tonia Pettitt, CMIP©, brings more than 40 years of experience guiding individuals and families through exactly these decisions. This page covers what you need to know before you enroll — the enrollment windows, the penalty rules, the coverage structure choices, the IRMAA exposure, and the coordination with Social Security and retirement income — so that the decisions you make at 65 support your retirement rather than complicate it. Medicare decisions do not exist in isolation; they intersect with your income strategy, your Social Security timing, and your long-term care planning in ways that require a coordinated approach.

Medicare — Key Costs, Deadlines, and Thresholds Every Enrollee Should Know

The numbers below reflect the official Medicare cost figures released by CMS and are the baseline for every enrollment and planning decision you make. Understanding these figures before enrollment prevents the surprises that most Medicare enrollees encounter only after they receive their first premium bill.

The Initial Enrollment Period — Your 7-Month Window

Most people become eligible for Medicare at age 65, and the Initial Enrollment Period spans seven months — the three months before your birthday month, the birthday month itself, and the three months after. Enrolling in the first three months of this window typically means coverage begins on the first day of your birthday month. Enrolling during months four through seven — after your birthday month — creates a coverage delay of one to three months depending on when you enroll. That timing matters when you are transitioning off employer coverage on a specific date and need Medicare to start seamlessly. Missing the IEP without qualifying coverage is one of the most consequential Medicare mistakes you can make. If you miss the IEP, you can only enroll during the General Enrollment Period running January 1 through March 31 each year, with coverage starting July 1 — creating a potential gap of six to eighteen months without Part B coverage, plus a permanent 10% per year late enrollment penalty that follows you for life. Our resource on Medicare enrollment mistakes to avoid covers this and the other most expensive timing errors that new enrollees make, and our resource on Medicare enrollment for people still working covers the Special Enrollment Period rules that apply when employer coverage allows a legitimate IEP delay.

Who Can Delay Part B Without Penalty — The Qualifying Coverage Rules

If you are still actively working at 65 and covered by an employer group health plan through your own or your spouse’s current employment, you may be able to delay Part B enrollment without incurring the late enrollment penalty. The operative word is “actively” — the coverage must come from current employment, not retirement. When you eventually leave active employment and lose that employer group health coverage, you enter a Special Enrollment Period (SEP) that allows you to enroll in Part B without penalty within eight months of losing the qualifying coverage. This SEP does not require you to apply the day you lose employer coverage — you have eight months — but it is a strict window and does not automatically extend. Our resource on Medicare enrollment for people still working covers the documentation requirements for the SEP, how to demonstrate the qualifying coverage to SSA, and the sequencing of enrollment steps when transitioning from employer coverage to Medicare. Our resource on does working past 65 affect Social Security benefits covers the related question of how continued employment past 65 interacts with both Medicare and Social Security filing decisions.

COBRA, Retiree Plans, and the Creditable Coverage Trap

Many people assume that maintaining any form of health coverage after retirement protects them from the Medicare late enrollment penalty. This is one of the most expensive misunderstandings in Medicare planning. COBRA continuation coverage — the temporary extension of your former employer’s group health plan after you leave employment — does not qualify as creditable coverage for purposes of delaying Medicare Part B without penalty. Retiree health coverage offered by a former employer also does not qualify. ACA marketplace plans do not qualify. Any form of individual health insurance purchased outside of an active employer group plan does not qualify. If you are on COBRA or retiree coverage at 65 and delay Part B enrollment based on the assumption that this protects you, you will face the permanent late enrollment penalty when you eventually need to enroll. The correct sequence is to enroll in Part B on time at 65 — even while continuing COBRA or retiree coverage — rather than delaying and accumulating penalty months. Our resource on HSA and retroactive Part A guide covers a related timing complexity: Medicare’s retroactive Part A enrollment can disqualify HSA contributions for prior months, creating an unexpected tax consequence for workers with Health Savings Accounts who do not time their Medicare enrollment carefully.

The Small Employer Rule — A Critical Special Case

Employers with fewer than 20 employees are subject to a different rule that catches many beneficiaries off guard. When an employer has fewer than 20 employees, Medicare is the primary payer for covered employees who are age 65 or older — even when the employer provides group health coverage. This means that at a small employer, your employer plan becomes secondary, and if you have not enrolled in Medicare, your employer plan may pay only a fraction of what it would have paid had Medicare been primary — or may refuse to pay entirely for services Medicare would have covered. The practical consequence of delaying Medicare at a small employer is that neither Medicare nor your employer plan may fully cover your medical bills: Medicare because you haven’t enrolled, your employer plan because it expects Medicare to be primary. Our resource on Medicare Part B explained covers the primary-secondary payer rules in detail, including how to verify whether your employer’s plan is primary or secondary at age 65 by asking your employer’s HR or benefits administrator about the company’s headcount.

Medicare Advantage vs. Medigap — The Structural Choice That Defines Your Coverage

Choosing between Medicare Advantage and Medigap (Medicare Supplement) is the most significant structural decision in Medicare planning — and it is one that is much harder to reverse than most people realize. Medicare Advantage plans bundle Parts A and B (and usually Part D) into a single plan managed by a private insurer. They typically offer lower monthly premiums, often as low as $0 per month in 2026, but come with defined provider networks, prior authorization requirements for some services, and copay structures that vary by service type. Medigap plans work alongside Original Medicare and pay the “gaps” that Medicare leaves — primarily the Part B 20% coinsurance and the Part A deductible — in exchange for higher monthly premiums that produce more predictable out-of-pocket costs. Original Medicare plus a Medigap policy typically provides broader provider access — any provider who accepts Medicare nationwide — without network restrictions. Our resource on best-rated Medicare Advantage companies covers the Advantage carrier landscape, and our resource on Medicare supplement coverage for cancer treatment covers a scenario where the Medigap access advantage is most material — when specialist access, provider choice, and treatment center flexibility matter most. Our detailed resource on Medicare Advantage vs. Medicare Supplement comparison provides the full side-by-side framework for evaluating which structure best fits your health profile, lifestyle, travel patterns, and financial priorities. The critical timing point: if you switch from Medicare Advantage to Medigap after your Medigap open enrollment period (the first six months after enrolling in Part B at 65 or older), you may face medical underwriting and can be denied coverage or charged higher rates based on health conditions. This makes the initial choice more consequential than it appears at enrollment.

Part D Drug Coverage — Penalty Risk and the Annual Review Requirement

Part D prescription drug coverage has its own late enrollment penalty — 1% of the national base beneficiary premium per month for each month you go without creditable drug coverage after first becoming eligible for Part D. Unlike the Part B penalty, the Part D penalty is calculated against a base premium that changes annually, but it still compounds meaningfully over time and is permanent for as long as you maintain Part D. Creditable drug coverage for Part D purposes includes most employer group drug coverage, VA drug benefits, and a few other specific programs — but not individual health plans that do not meet the creditable coverage standard. Even if you do not currently take any prescription medications, failing to enroll in a Part D plan at 65 without creditable coverage creates penalty exposure that will cost you money when you do need drug coverage later. The 2026 Part D out-of-pocket cap is $2,100 — a significant protection introduced by recent legislation that limits total drug spending before catastrophic coverage kicks in and Medicare covers 100%. For high-volume medication users, this cap changes the cost calculation meaningfully. Our resource on how to choose the best Medicare plan provides the structured decision framework for evaluating both drug plan and plan type choices, and our resource on Medicare Part D explained covers the formulary, tier structure, and pharmacy network mechanics that determine real out-of-pocket drug costs.

IRMAA — How Retirement Income Affects Your Medicare Premiums

IRMAA — the Income-Related Monthly Adjustment Amount — is a Medicare premium surcharge applied to Part B and Part D premiums for beneficiaries whose income exceeds defined thresholds. In 2026, IRMAA applies when modified adjusted gross income exceeds $109,000 for individuals or $218,000 for married couples filing jointly. The critical planning point: IRMAA is based on income from two years prior — meaning your 2026 Medicare premiums are determined by your 2024 tax return. A one-time income event in 2024 — a Roth conversion, a real estate sale, a large IRA distribution, or a business liquidity event — can trigger IRMAA in 2026 even if your ongoing retirement income would not normally exceed the threshold. At the highest income tier (above $500,000 individual / $750,000 joint), the 2026 Part B premium reaches $689.90 per month — more than triple the standard premium. Our resource on required minimum distributions covers how RMD income — which becomes mandatory starting at age 73 — can push MAGI above IRMAA thresholds in later years, a planning consideration for Medicare beneficiaries who are also managing qualified retirement accounts. Our resource on is Social Security taxable covers how Social Security income contributes to combined income calculations, and our resource on how to minimize Social Security taxes covers income sequencing strategies that can reduce the combined income that determines IRMAA surcharges. For former public sector workers who recently had Social Security benefits restored through the Social Security Fairness Act repeal of GPO and WEP, our resource on government pension offset explained covers how restored Social Security income may now push MAGI above IRMAA thresholds for the first time — a new planning consideration for this population.

Medicare Does Not Cover Long-Term Care — Understanding the Gap

One of the most consequential misconceptions about Medicare is what it does not cover. Medicare is primarily designed for acute medical care — hospitalization, physician services, outpatient treatment, short-term skilled nursing following a qualifying hospital stay, and medically necessary home health services. It does not pay for extended custodial care — the ongoing assistance with activities of daily living such as bathing, dressing, meal preparation, medication management, and dementia-related supervision that constitute the majority of long-term care costs in the United States. The average cost of a private room in a nursing facility exceeds $100,000 per year; home health aide services cost $25-$30 per hour and add up quickly at full-time care levels. Medicaid covers long-term care for those who have spent down to poverty-level assets — a position that most middle-income retirees spend years of retirement savings reaching. Understanding this gap before Medicare enrollment allows you to evaluate long-term care strategies separately and before a health crisis makes the options narrower. Our resource on long-term care insurance services covers the range of strategies available for funding extended care needs — including traditional long-term care insurance, hybrid life/LTC products, and annuity-based LTC riders — that are worth evaluating before or alongside your Medicare enrollment decision.

Coordinating Medicare With Social Security Timing

Medicare and Social Security are separate programs with separate enrollment rules — but their financial consequences are deeply intertwined. Delaying Social Security past 65 while enrolling in Medicare means you pay Part B and Part D premiums out of pocket rather than having them deducted from a Social Security check. This is a cash flow consideration but not a barrier. More importantly, IRMAA surcharges are determined by income before Social Security begins — so Roth conversions, IRA withdrawals, and other income events in the years before you claim Social Security affect Medicare premiums through the two-year IRMAA lookback. Once you begin Social Security, your Part B premium is deducted directly from your monthly check. If your Part B premium increases due to IRMAA, that deduction grows proportionally. Our resource on how Medicare and Social Security work together covers the full coordination framework between these two programs. Our resource on maximize Social Security benefits covers the claiming strategy dimension, and our resource on delayed retirement credits and Social Security payout increases covers the mechanics of the 8% per year Delayed Retirement Credit that rewards waiting past Full Retirement Age — a decision that must be coordinated with the Medicare enrollment and IRMAA exposure created by the income sources used to bridge to the later claiming date. For widowed beneficiaries navigating both Medicare and survivor Social Security benefit decisions simultaneously, our resource on strategies for claiming Social Security for widows covers the specific rules and optimization strategies that apply. Our resource on Social Security services covers the full planning landscape for both programs in coordination.

Annual Review — Why Enrollment Is Not a One-Time Decision

Medicare enrollment is not a one-time decision that resolves itself. The Annual Enrollment Period — October 15 through December 7 each year — is when beneficiaries can switch between Medicare Advantage plans, switch between Medicare Advantage and Original Medicare, and change Part D drug plans. Changes made during AEP take effect January 1. Because drug plan formularies, premiums, and pharmacy networks change annually, a plan that was optimal last year may no longer be the best fit for your current prescription profile. Because Medicare Advantage networks and cost-sharing structures also change annually, it is worth reviewing your Advantage plan each year to ensure your doctors remain in-network and the plan continues to meet your needs. Medicare Supplement plans do not have open enrollment each year — you can generally keep a Medigap plan as long as you pay the premiums — but the premium can change annually. Our resource on Medicare calculator provides a tool for modeling your plan options, and our resource on Medicare services covers how our team approaches the annual review process alongside ongoing Medicare planning.