Medicare Part B: The $185/Month Medical Insurance That Could Cost You $592 — Here's Why

Medicare Part B costs $185 per month in 2026 — unless you made "too much" money two years ago, in which case it could cost you $591.90. Welcome to IRMAA, the Income-Related Monthly Adjustment Amount that hits 7% of Medicare beneficiaries with surprise premium surcharges based on their 2024 tax returns. And here's the kicker: Part B comes with unlimited financial exposure through its 20% coinsurance, meaning there's literally no cap on what you could owe (unlike Medicare Advantage plans, which are required to limit your annual out-of-pocket costs to $8,850 in 2026).

The IRMAA Income Trap: What You'll Actually Pay for Part B

Medicare uses your Modified Adjusted Gross Income (MAGI) from two years ago to determine your Part B premium. Made $106,001 as a single filer in 2024? You're paying 40% more than the standard premium in 2026. Here's the complete breakdown:

The Two-Year Time Bomb

IRMAA uses your 2024 tax return to set your 2026 premiums, creating a brutal delay that catches retirees off-guard. Sold your business in 2024? Had a one-time capital gain? You'll pay the IRMAA penalty throughout 2026, even if your current income qualifies for the standard premium. Appeals are possible but require documentation that your income has permanently decreased due to marriage, divorce, death of a spouse, work stoppage, or loss of pension — temporary fluctuations don't count.

The 20% Coinsurance Trap: Why Original Medicare Has No Safety Net

After you meet Part B's $257 annual deductible in 2026, you pay 20% of Medicare-approved amounts for covered services — forever. There is no annual out-of-pocket maximum. No cap. No "you've suffered enough" threshold. If you rack up $500,000 in covered medical expenses in a year, you owe $100,000 (plus the deductible).

What Part B Covers (And What It Doesn't)

Part B covers physician services, outpatient procedures, preventive care, durable medical equipment, and some home health services. It doesn't cover long-term care, dental, vision, hearing aids, or prescription drugs (that's Part D territory). The 20% coinsurance applies to everything except preventive services, which are covered at 100% when you use in-network providers.

Premium Inflation: How Part B Costs Have Outpaced Everything

Medicare Part B premiums have risen 175% since 2000, compared to 65% general inflation over the same period. The $45.50 monthly premium in 2000 would be $75.10 today adjusted for general inflation — instead, it's $185, a 146% premium to the inflation rate.

What Drives Part B Premium Increases

Part B spending grows 4-6% annually, driven by physician fee increases, new expensive treatments, and demographic pressure as baby boomers age into Medicare. CMS sets premiums to cover 25% of Part B costs (the other 75% comes from general revenue), but medical inflation consistently outpaces the government's ability to control spending.

Late Enrollment Penalties: The 10% Lifetime Tax

Miss your initial enrollment period for Part B, and you'll pay a 10% penalty for every 12-month period you were eligible but didn't enroll. This penalty is permanent — you'll pay it for as long as you have Part B coverage. Delayed enrollment by 24 months? Your $185 monthly premium becomes $222. Forever.

The penalty calculation: 10% × number of 12-month periods without coverage × current Part B premium. So if you delayed for 36 months and the current premium is $185, your monthly cost becomes $240.50 ($185 × 1.30).

Why Medigap Exists: Plugging the Coverage Holes

The unlimited 20% coinsurance exposure is why 14.7 million Medicare beneficiaries (about 44% of those with Original Medicare) purchase Medigap supplemental insurance. Medigap Plan F and Plan G cover the Part B coinsurance entirely, transforming unpredictable medical costs into fixed monthly premiums.

Assignment vs. Non-Assignment: The Hidden Billing Trap

Not all doctors "accept assignment" — meaning they don't always accept Medicare's approved amount as payment in full. Non-participating providers can charge up to 15% above Medicare's approved amount, and you pay the difference. On a $1,000 procedure, that's an extra $150 out of your pocket, on top of the standard 20% coinsurance.

About 93% of physicians accept Medicare assignment, but specialists in affluent areas are more likely to opt out entirely or balance bill the 15% excess. Always confirm assignment status before treatment to avoid surprise bills.

Medicare Part B vs. Medicare Advantage: The Cost Reality

With 33 million Americans now enrolled in Medicare Advantage (51% of all Medicare beneficiaries), the traditional Part B + Medigap combination faces serious competition. MA plans average $17.30/month in premiums and cap annual out-of-pocket costs at $8,850, compared to Part B + Plan G costing $335-385/month with no network restrictions.

Bottom Line: Part B Is Expensive Insurance That Leaves You Exposed

Medicare Part B costs $185/month for most beneficiaries in 2026 — but that's just the entry fee. The 20% coinsurance with no annual cap means you could owe tens of thousands in a bad health year. High earners pay up to $592/month for the same coverage, subsidizing the system for everyone else.

If you're keeping Original Medicare, budget for Medigap to cover the coinsurance gaps — the combined cost of Part B + Plan G ranges from $335-385/month but provides predictable costs and unlimited provider choice. If that's too expensive, Medicare Advantage plans offer lower premiums ($17.30 average) and capped out-of-pocket costs ($8,850 maximum) but restrict your provider network.

The one thing you can't do: skip Part B entirely. Unless you have qualifying employer coverage, the 10% late enrollment penalty makes delayed enrollment increasingly expensive. Medicare's betting you'll need medical care eventually — and they're probably right.