IRMAA Brackets 2026 (MFJ): Where Couples Cap Conversions

The decision: $18,000 more conversion, or stop at the ceiling?

Tom and Linda are 66, both on Medicare, and file jointly. They live in Arizona (4.5% flat state income tax) and are mid-way through a multi-year Roth conversion plan to drain their traditional IRAs before required minimum distributions start at 73. This year their MAGI — before any conversion — sits at $222,000 from a pension, Social Security, and a partial conversion already done in January.

Their advisor’s spreadsheet says they have “room” in the 24% bracket all the way to $394,600. So they’re tempted to convert another $36,000 this year, which would push MAGI to $258,000. That feels safe — it lands them right at the top of the $206K–$258K IRMAA tier, premium unchanged.

But the spreadsheet only modeled income tax. It ignored Medicare. And there’s a $258,000 wall the income-tax view can’t see: convert one dollar past it, and both spouses’ Part B premiums jump from $259 to $370/mo — a household hit of $3,182.40 per year that has nothing to do with their tax bracket. Here is how the ceiling math actually resolves.

2026 IRMAA brackets for married filing jointly

IRMAA — the Income-Related Monthly Adjustment Amount — is a surcharge added to your Medicare Part B and Part D premiums when your income is high. It’s authorized under the Social Security Act §1839(i) and administered by SSA using MAGI reported to the IRS. For a married couple filing jointly, the surcharge is set by your combined MAGI, and it applies to each spouse enrolled in Medicare.

Critically, the tiers use a two-year lookback: your 2026 premiums are based on the MAGI from your 2024 tax return. So a conversion you do in 2026 sets the surcharge you’ll pay in 2028. Here are the 2026 MFJ tiers (CMS, based on 2024 MAGI):

The household annual surcharge column is the number most people never calculate: it’s the premium above the $185 base, totaled for both spouses across 12 months. That’s the real cost of each tier — and the step between tiers is what should drive your conversion ceiling.

The math behind each household number

The formula for any tier’s annual household surcharge is straightforward:

(Tier Part B − $185 base + Part D surcharge) × 2 spouses × 12 months

At the $206K–$258K tier: ($259 − $185 + $13.70) × 2 × 12 = $87.70 × 24 = $2,104.80/yr. At the $258K–$322K tier: ($370 − $185 + $35.30) × 2 × 12 = $220.30 × 24 = $5,287.20/yr. The step from tier 1 to tier 2 is therefore $5,287.20 − $2,104.80 = $3,182.40. That is the penalty for crossing $258,000.

Why $258K is a cliff, not a slope

IRMAA is not phased in. There is no gradual ramp where each extra dollar adds a few cents of premium. It is a pure cliff: at $258,000 of MAGI you pay the tier-1 premium, and at $258,001 you pay the full tier-2 premium for the entire year — both spouses, all 12 months.

That single dollar over the line costs your household $3,182.40. The effective marginal “tax rate” on that one dollar is, mathematically, 318,240%. Obviously you’d never trip the cliff for $1 on purpose — the point is that the cost is fixed regardless of how far over you go. Whether you cross by $1 or by $5,000, the surcharge step is identical: $3,182.40. So if you’re going to cross, cross with purpose and fill the tier; if you’re not, leave a buffer.

Resolving Tom and Linda’s $18K decision

Back to the couple at $222,000 MAGI considering another $36,000 conversion. Split the decision into the part that’s clearly safe and the part that crosses the cliff.

• The first $36,000 lands them at $258,000 exactly. This stays inside the $206K–$258K tier. No premium change. They’re already paying the tier-1 surcharge regardless, so there’s no incremental IRMAA cost on this slice — only the 24% federal income tax on the conversion.
• The next $18,000 (taking MAGI to $276,000) crosses into tier 2. Now the surcharge step lands.

Here is the true all-in cost of that last $18,000 of conversion:

That last $18,000 of conversion costs them at a 46.2% effective rate — nearly double the 24% their spreadsheet showed. The IRMAA step is a one-year cost (it resets each year based on that year’s MAGI), while the conversion benefit is permanent, so it isn’t an automatic “no.” But it changes the answer. The decision lever: convert up to $258,000 this year, and push the remaining $18,000 into next year — spreading two conversions across two tax years so neither one trips the second IRMAA tier.

What most people miss: the surcharge is per person, the trigger is joint

The single biggest misconception is that IRMAA is a household premium. It is not. Each Medicare-enrolled spouse pays their own Part B premium and their own Part D surcharge — but both are dictated by the same combined MFJ MAGI. This has two consequences couples routinely overlook:

1. One income event doubles itself. If Linda takes a $40,000 IRA withdrawal that nudges household MAGI over $258K, both she and Tom pay the higher $370 Part B premium — even though Tom had no income of his own. The surcharge applies per enrolled body, not per income earner.
2. The thresholds are not double the single thresholds. The single-filer first tier starts at $103K; the MFJ first tier starts at $206K — almost exactly double. But the dollar surcharges per person are identical to a single filer’s. A married couple isn’t penalized on the rate; they’re exposed on the count, because the same MAGI triggers two surcharges instead of one.

A second commonly-missed point: the two-year lookback means a one-time income spike — a Roth conversion, a home sale, an inherited-IRA lump sum — raises premiums two years later, often the very year a spouse retires and income drops. If your income has fallen since the lookback year because of a life-changing event (work stoppage, marriage, divorce, death of a spouse), file Form SSA-44 to request a redetermination. SSA can use your current, lower income instead of the two-year-old figure. A voluntary Roth conversion does not qualify as a life-changing event — but retirement does.

The single-filer trap waiting for the surviving spouse

Here is the planning angle most couples never model. The $258K ceiling exists only while both spouses are alive and filing jointly. When one spouse passes, the survivor files single the following year — and the single IRMAA thresholds are roughly half the joint ones. The survivor’s first tier hits at $103K, and the $370 tier hits at just $129K.

So the same retirement income that kept a couple comfortably under $206K can shove a surviving spouse into the $129K–$161K tier — paying $370/mo Part B as a single person. This is the “widow’s penalty” in its Medicare form, and it’s a reason to do more Roth conversions while both spouses are alive (filling the wide MFJ brackets) rather than leaving large traditional-IRA balances that will be drawn down by one survivor against the narrow single thresholds.

How to set your conversion ceiling each year

The targeting process for a married couple is mechanical once you accept that IRMAA, not just the tax bracket, sets the wall:

1. Project your baseline MAGI before any conversion: pension, Social Security (the taxable portion), interest, dividends, capital gains, RMDs, and any wages.
2. Identify the next IRMAA threshold above your baseline. If you’re at $222K, your next wall is $258K, leaving $36K of conversion room before the step.
3. Compare the marginal value of crossing. Crossing costs the tier step ($3,182 from tier 1 to tier 2) plus the income tax on the conversion. Is the long-term RMD relief and future-tax savings worth that one-year surcharge? Often the answer is “fill this tier, cross next year.”
4. Leave a safety buffer. Don’t aim for exactly $258,000. A surprise year-end capital gains distribution from a mutual fund, or a slightly higher dividend, can push you $500 over and trip the whole surcharge. Target $253K–$255K to leave headroom.
5. Re-run it every year. The thresholds adjust for inflation, your baseline income shifts with RMDs and Social Security COLAs, and your conversion runway shortens as RMD age approaches.

When crossing the cliff is the right call

Stopping at $258K is the default, not a rule. Crossing into tier 2 makes sense when the conversion clearly outruns the one-year $3,182 surcharge:

• Large traditional-IRA balance + early in the conversion window. A couple with $2M in pre-tax IRAs at 66 has only seven years before RMDs at 73. If filling the 24% bracket now prevents being forced into the 32% bracket (and higher IRMAA tiers) on RMDs later, the math favors crossing.
• The widow’s-penalty risk is high. A meaningful age or health gap between spouses raises the odds that one survivor draws down a large balance against single thresholds. Converting aggressively while MFJ is the hedge.
• You expect higher rates after a future TCJA expiration. The current 24% MFJ bracket runs to $394,600. If you believe rates rise, locking in conversions at today’s rates can outweigh a single year’s surcharge.

The decision lever

For a married couple at $240K–$258K MAGI, the conversion ceiling is $258,000 — not your tax bracket’s $394,600. The last $18,000 that crosses into tier 2 carries an effective cost near 46% once the $3,182 household IRMAA step is layered onto the 24% federal and your state tax. Convert up to the ceiling, push the overflow into next January, and re-target each year against the inflation-adjusted threshold. Cross deliberately only when a large pre-tax balance, a wide spousal age gap, or expected future rate increases make the one-year surcharge a price worth paying — and when you do cross, fill the tier rather than tiptoe one dollar past it.