How Medicare Part B Gets Its Funding

Medicare Part B is funded through three main sources: premiums paid by people enrolled in the program, general tax revenue from the federal government, and interest earned on the Medicare trust fund. Unlike Part A, which is funded primarily through payroll taxes, Part B relies on a mix of beneficiary contributions and general federal dollars. This means your Part B premium covers only part of the actual cost — the government covers the rest.

The exact split changes each year. Currently, beneficiaries pay roughly 25 percent of Part B costs through their monthly premiums, while the federal government pays the remaining 75 percent from general tax revenue. This is why Part B premiums rise when medical costs rise, and why Congress sometimes adjusts the percentage split when the program's costs grow faster than expected.

Key Takeaways

  • Part B premiums come directly from your Social Security check or bank account, but they cover only about one-quarter of the actual cost of the program.
  • The federal government pays the other three-quarters of Part B costs using general tax revenue, not a dedicated payroll tax like Part A.
  • Part B premiums increase each year based on rising healthcare costs, and the amount varies depending on your income level.
  • Higher-income beneficiaries pay additional surcharges on top of the standard Part B premium, a system called Income-Related Monthly Adjustment Amounts (IRMAA).

Where Your Part B Premium Dollar Goes

When you pay your monthly Part B premium, that money goes into the Supplementary Medical Insurance Trust Fund, a separate account managed by the Centers for Medicare & Medicaid Services (CMS). The trust fund then pays doctors, hospitals, and other providers for the services you receive — office visits, lab tests, imaging, outpatient surgery, and durable medical equipment like wheelchairs or oxygen tanks.

The trust fund operates on a pay-as-you-go basis, meaning current premiums and federal contributions pay for current beneficiaries' care. If the fund runs low, Congress can increase premiums or adjust the beneficiary/government cost split. This is different from Part A, which has its own dedicated payroll tax stream and operates with a separate trust fund.

Federal Tax Revenue and the Government's Share

The 75 percent of Part B costs paid by the federal government comes from general tax revenue — income taxes, corporate taxes, and other federal sources. This is not a separate Medicare tax; it is money from the general Treasury. When Congress debates the federal budget, Part B funding is part of that conversation, which means Part B costs can affect other government spending priorities.

This funding structure means Part B is subject to annual appropriations decisions. If Congress does not allocate enough general revenue to cover the expected costs, premiums must rise to make up the difference. This is why Part B premiums sometimes jump significantly from one year to the next, even if your own healthcare use has not changed.

Income-Related Premiums and Higher Earners

If your income exceeds a certain threshold, you pay a higher Part B premium through a system called Income-Related Monthly Adjustment Amounts (IRMAA). In 2024, for example, single filers with income over $97,000 and married couples filing jointly with income over $194,000 pay additional surcharges on top of the standard premium. The surcharge can be substantial — as much as three times the standard premium for the highest earners.

IRMAA is calculated based on your tax return from two years prior. So your 2024 premium is based on your 2022 income. If your income drops significantly — through retirement, job loss, or a major life event — you can request that CMS recalculate your IRMAA using your current year's income instead. This requires filing a form and providing documentation of the change.

How Part B Premiums Are Set Each Year

Every October, CMS announces the standard Part B premium for the following year. The premium is calculated to cover the expected costs of the program, adjusted for inflation and changes in healthcare utilization. The announcement includes the dollar amount and the percentage increase from the previous year.

The premium takes effect on January 1 for most people, though those already on Medicare see the new premium deducted from their January Social Security payment. If you enroll in Part B for the first time after age 65, you may pay a permanent penalty of 10 percent per year of delayed enrollment, added to your premium for as long as you have Part B. This penalty is one reason to enroll during your initial enrollment period, even if you do not yet need medical care.

The Difference Between Part A and Part B Funding

Part A is funded through the Hospital Insurance Trust Fund, which is fed by payroll taxes (1.45 percent from employees and 1.45 percent from employers, plus an additional 0.9 percent for high earners). Part A has no monthly premium for most people who have paid into Medicare through their working years. Part B, by contrast, requires a monthly premium from everyone, regardless of work history, because it is funded differently.

This distinction matters when you hear about Medicare's financial health. When news reports say the Part A trust fund is running low, that is a separate issue from Part B funding. Part A faces pressure because healthcare costs are rising faster than payroll tax revenue. Part B does not face the same solvency crisis because it is funded through general revenue, which Congress can adjust annually.

What Happens If Part B Costs Rise Faster Than Expected

If medical costs spike unexpectedly, the Supplementary Medical Insurance Trust Fund can draw down its reserves temporarily. However, the fund is designed to remain solvent by adjusting premiums. Congress has the authority to change the beneficiary/government cost split, though doing so is politically difficult because it means either raising premiums or cutting provider payments.

In recent years, Part B premiums have risen faster than Social Security benefits, which means some beneficiaries see their purchasing power decline even though their benefits increase. This is one reason to review your Part B coverage each year during the Annual Enrollment Period (October 15 to December 7) and consider whether a Medigap or Medicare Advantage plan might better suit your needs and budget.

Frequently Asked Questions

Why does my Part B premium keep going up?

Part B premiums rise when the cost of medical services covered by Part B increases. The premium is recalculated each year to may support the trust fund remains solvent. If you have higher income, your premium may also increase due to IRMAA surcharges. Premiums are announced in October for the following year.

Can I avoid paying Part B premiums?

If you are enrolled in Medicare, you must pay the Part B premium unless you have very low income and may have access to for Medicaid to pay it for you. Some people delay Part B enrollment if they have employer coverage, but once you enroll, you pay the premium. Delaying enrollment without may have access to coverage results in a permanent penalty.

Does my Part B premium cover everything Medicare Part B pays for?

No. Your premium covers only about 25 percent of Part B costs. The federal government covers the remaining 75 percent from general tax revenue. This is why your out-of-pocket costs (deductibles and coinsurance) can still be substantial even after you pay your premium.

What is IRMAA and how does it affect my premium?

IRMAA stands for Income-Related Monthly Adjustment Amounts. If your income exceeds certain thresholds, you pay an additional surcharge on top of your standard Part B premium. The surcharge is based on your tax return from two years prior. You can request a recalculation if your income has dropped due to retirement or a major life event.

Is Part B funding in trouble like Part A is?

Part B does not face the same solvency concerns as Part A because it is funded through general tax revenue that Congress can adjust annually. However, rising medical costs do put upward pressure on premiums. Part A is funded through payroll taxes, which grow more slowly than healthcare costs, creating a different financial challenge.