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A higher savings rate is good news for retirees. Every dollar of interest a bank pays you is also taxable income, and Medicare uses income to set what higher-earning beneficiaries pay for Part B and Part D. If a large cash balance earns enough interest, it can push you over an income line and raise your Medicare premiums for a full year. Your coverage remains the same.

The charge is called the income-related monthly adjustment amount, or IRMAA. CMS says it affects roughly 8% of people with Part B. Because so few people pay it, most retirees never plan for it. In 2026 the standard Part B premium is $202.90[1] a month. A retiree whose income lands just over the first line pays $284.10[1].

IRMAA is based on modified adjusted gross income (MAGI) from a tax return filed two years earlier. IRS Publication 915 shows the pattern. It says the 2025 Part B premium could be higher if the MAGI on your 2023 federal income tax return was greater than $106,000 ($212,000 if married filing jointly). That means the interest you earn this year affects the premium you pay two years from now.

For most retirees, MAGI starts with the adjusted gross income on Form 1040, and interest goes straight into it. IRS Publication 17 says taxable interest includes interest you receive from bank accounts. Credit unions call their payouts “dividends,” but those are reported as interest too. CD interest generally counts in the year you receive it or can take it without a substantial penalty.

The interest on Treasury bills, notes and bonds appears in box 3 of Form 1099-INT. IRS Publication 550 says it is generally added to your other taxable interest.

Part D has its own surcharge with the same income lines. It is added on top of your drug plan premium and is deducted from Social Security benefit checks or paid directly to Medicare.

IRMAA works in levels, and each levels has a hard edge. The surcharge applies in full at each threshold. Once your MAGI tops a threshold by any amount, you pay the full premium for the next levels.

In 2026 the first surcharge starts at income over $109,000[1] for single taxpayers and over $218,000 for joint taxpayers. At or below those amounts, you pay the standard $202.90[1]. Just above them, Part B adds $81.20[1] a month and Part D adds $14.50. The higher levels work the same way. Over $137,000[1] single or $274,000 joint, the total Part B premium rises to $405.80. The top levels reaches $689.90[1].

Here is a hypothetical example. A married couple has pensions, Social Security and required withdrawals that put them a few thousand dollars under the joint line. They move a large cash reserve from a checking account paying almost nothing into a high-yield account. The new interest alone could be enough to cross the line.

The surcharge is charged per beneficiary, so when both spouses are on Medicare, each one pays it.

Start by knowing where you stand. Take the adjusted gross income from last year’s return, estimate this year’s, and see how far each is from the thresholds. If you’re well below the line, a higher rate costs you nothing extra.

If you’re close, timing matters. Publication 17 says interest on a CD of one year or less that pays at maturity counts when you receive it. Choosing whether a CD matures in December or January determines which tax year that interest lands in. You can also spread large IRA withdrawals or Roth conversions over several years instead of taking them all at once.

Where you hold your cash matters too. Interest earned inside a traditional IRA is tax-deferred until you take it out. Interest inside a Roth IRA is generally not taxable. Keeping some cash-like holdings inside those accounts keeps that interest off this year’s return.

If your income has dropped since the year Medicare is using, you can ask Social Security to recalculate. Form SSA-44 lets beneficiaries who had a major life-changing event and lower income request a smaller surcharge. Qualifying events include retirement or stopping work and the death of a spouse. Social Security determines each request.

A higher rate can still be worth keeping. Each levels has a fixed, published cost. Consider that cost against the interest you would give up before moving money anywhere. IRMAA is only one of several Medicare costs that scale with income or catch retirees off guard, and we mapped the rest (coverage gaps, premium traps, the surcharges linked to income from two years ago) here: Medicare’s Hidden Bills.

Once you know where the thresholds are, you can usually earn the higher rate and avoid a surprise.

Your next step is to put last year’s and this year’s income next to the current thresholds. The figures above are 2026 amounts from CMS, and CMS updates the table every year, so check the latest version before making a large withdrawal or moving a big balance.

Yes. Interest from bank savings accounts, CDs and Treasuries is taxable interest, so it goes into the adjusted gross income that starts the IRMAA calculation.

Medicare uses MAGI from the tax return filed two years earlier. Interest you earn this year shows up in your premium two years from now.

Yes. Each levels has a hard edge. In 2026, a single taxpayers just over $109,000[1] pays the full $284.10 Part B premium for that levels.

Not while it stays in the account. Traditional IRA interest is taxed when you take it…