Medicare Part B Explained: Premiums, IRMAA, and Enrollment in 2026

Medicare Part B is the part of Original Medicare that pays for the everyday medical care most people actually use: doctor visits, lab work, preventive screenings, outpatient surgery, physical therapy, ambulance rides, mental health care, and durable medical equipment such as walkers, wheelchairs, and blood-sugar monitors. Unlike Part A (hospital insurance), which the vast majority of people get premium-free, Part B always carries a monthly premium, and in 2026 the standard premium is $202.90 a month. The key takeaway is simple but valuable: signing up for Part B on time, and knowing whether your income triggers a surcharge, can save you hundreds of dollars a month and spare you a penalty that never goes away.

This guide explains what Part B covers, what it costs in 2026 (including the annual deductible and the 20% coinsurance that surprises many new enrollees), how the income-related monthly adjustment amount (IRMAA) raises premiums for higher earners, when and how to enroll, and how Part B fits together with Medicare Advantage and Medigap. Wherever we cite a 2026 dollar figure, remember that these amounts are set and indexed each year by the Centers for Medicare & Medicaid Services (CMS) and the Social Security Administration (SSA), so always confirm the current-year number before making a decision.

What Medicare Part B Actually Covers

Part B is often called medical insurance, and it covers two broad categories of care. The first is medically necessary services — the care you need to diagnose or treat a condition, including office visits, specialist consultations, outpatient procedures, diagnostic tests, X-rays, chemotherapy, dialysis, and mental health services. The second is preventive care designed to catch problems early or keep you healthy, such as the annual wellness visit, most vaccines, cancer screenings, cardiovascular screenings, and diabetes management. Most preventive services are covered at no cost to you when you see a provider who accepts Medicare assignment.

Part B also covers a range of items and services people do not always associate with medical insurance: durable medical equipment, prosthetics and orthotics, limited outpatient prescription drugs administered in a clinic (like certain injectables), and ambulance transportation when other transportation could endanger your health. What Part B does not cover is just as important to know. It generally does not pay for long-term custodial care, most dental care, routine eye exams for glasses, hearing aids, or most prescription drugs you fill at a pharmacy — that last category is the job of Part D.

What Part B Costs in 2026: Premium and Deductible

For 2026, the standard Part B premium is $202.90 per month, up from $185.00 in 2025. Most people pay exactly this amount, and if you receive Social Security benefits, the premium is deducted automatically from your monthly check. Before Medicare starts paying its share of your care, you must first meet the annual Part B deductible, which is $283 in 2026 (up from $257). You pay that deductible once per calendar year, not per service.

These figures change every year. CMS announces the new premium and deductible each fall, and the amounts move based on projected program spending. A federal rule also protects most Social Security recipients: in years when the cost-of-living adjustment is small, your Part B premium increase generally cannot exceed the dollar increase in your Social Security benefit — a protection often called the hold-harmless provision. Because these numbers are re-set annually, treat any specific dollar figure as a snapshot and verify the current-year amount at Medicare.gov.

The 20% Coinsurance: Why Part B Alone Can Leave You Exposed

Here is the part that catches many people by surprise. After you meet the deductible, Original Medicare does not pay 100% of your covered Part B services. Instead, Medicare typically pays 80% of the Medicare-approved amount, and you are responsible for the remaining 20% coinsurance — with no annual cap on how much that 20% can add up to. For a routine doctor visit, 20% is trivial. For an expensive course of treatment, chemotherapy, or a major outpatient surgery, that open-ended 20% can reach thousands of dollars in a single year.

This is the single biggest reason people do not rely on Part A and Part B by themselves. To close the gap, most beneficiaries add either a Medigap (Medicare Supplement) policy, which helps pay that coinsurance and other cost-sharing, or they enroll in a Medicare Advantage (Part C) plan, which bundles coverage and includes an annual out-of-pocket maximum. We cover how those choices interact with Part B below.

IRMAA: When Higher Earners Pay More

Most people pay the standard premium, but higher-income beneficiaries pay an income-related monthly adjustment amount (IRMAA) on top of it — and a separate IRMAA surcharge on their Part D drug coverage. IRMAA is not a flat tax; it works as a series of income brackets, and crossing a threshold by even one dollar bumps you into the next tier. The table below shows the 2026 brackets, based on the modified adjusted gross income (MAGI) from your tax return, along with the total monthly Part B premium and the additional Part D surcharge for each tier.

People who are married but file separately follow a different, compressed set of thresholds and should check the SSA figures directly. The Part D surcharge shown is added to whatever your individual drug plan charges; you pay it even though the plan itself is run by a private insurer. As with every figure in this guide, these brackets are indexed annually, so confirm the current-year numbers before assuming where you land.

How IRMAA Is Determined — and How to Appeal

IRMAA is based on a two-year lookback: your 2026 surcharge is calculated from the MAGI on your 2024 tax return, because that is the most recent return the IRS has shared with Social Security. That lag matters, because a one-time spike in income — selling a home, taking a large IRA distribution, or realizing capital gains — can push you into a higher bracket two years later, even if your income has since dropped.

If your income has fallen because of a specific life-changing event — marriage, divorce, the death of a spouse, retirement or reduced work hours, loss of a pension, or an employer settlement — you can ask Social Security to use more recent income instead. You do this by filing Form SSA-44 and providing documentation. If you simply disagree with the determination, you also have the right to appeal (request a reconsideration). Do not ignore an IRMAA notice; responding promptly with the right paperwork is often the difference between paying the surcharge and having it removed.

When and How to Enroll in Part B

Most people become eligible for Medicare at age 65. Your first chance to sign up is the Initial Enrollment Period (IEP), a seven-month window that starts three months before the month you turn 65, includes your birthday month, and ends three months after. If you are already receiving Social Security benefits, you are usually enrolled in Part A and Part B automatically. If you are not yet collecting Social Security, you must actively sign up through the Social Security Administration, online or by phone.

There is a crucial exception. If you (or your spouse) are still working and covered by an employer group health plan based on that active employment, you may be able to delay Part B without penalty and enroll later through a Special Enrollment Period. But if you miss your window and do not have qualifying coverage, you can face a lifelong late-enrollment penalty — the standard premium rises 10% for each full 12-month period you could have had Part B but did not. Because the rules around employer coverage are easy to get wrong, verify your situation before turning down Part B.

How Part B Works With Advantage and Medigap

Part B is the foundation for the rest of your Medicare choices, and you must keep paying the Part B premium no matter which path you pick. From there, you generally choose one of two directions. In the first, you keep Original Medicare (Parts A and B) and add a Medigap policy to cover the 20% coinsurance and deductibles, plus a stand-alone Part D plan for drugs. This route offers broad provider access — any doctor who accepts Medicare — and predictable costs, at the price of an additional monthly premium.

In the second direction, you enroll in a Medicare Advantage (Part C) plan offered by a private insurer. These plans bundle Part A, Part B, and usually Part D, and they include an annual out-of-pocket maximum that Original Medicare lacks. In exchange, you typically use a provider network and may need referrals or prior authorization. Either way, Part B is required: you cannot buy a Medigap policy or join most Medicare Advantage plans without first being enrolled in Part B and paying its premium.

The Bottom Line

Part B is the workhorse of Original Medicare, covering the doctor visits, tests, and outpatient care you are most likely to use. For 2026, plan on a $202.90 standard monthly premium, a $283 annual deductible, and a 20% coinsurance with no cap — which is exactly why most people pair Part B with a Medigap policy or a Medicare Advantage plan. If your income is above $109,000 (single) or $218,000 (married filing jointly), budget for an IRMAA surcharge based on your income from two years earlier, and file Form SSA-44 if a life-changing event has since lowered your income.

Above all, watch your enrollment timing. Signing up during your Initial Enrollment Period, or using a valid Special Enrollment Period while you have employer coverage, keeps you clear of a permanent late penalty. Because every dollar amount here is updated annually by CMS and SSA, treat these 2026 figures as a starting point and confirm the current-year numbers at Medicare.gov or SSA.gov before you act.