IRMAA Second Cliff: $129K Costs $1,591/Yr (Single Filer)

Margaret, a 68-year-old single retiree in Phoenix, Arizona, has $120,000 of MAGI this year before any Roth conversion: $40,000 Social Security (85% taxable), a $55,000 pension, and $25,000 of dividends and interest. Her tax preparer suggests converting another $9,000 from her traditional IRA to her Roth “to fill up the 22% bracket.” That conversion would push her MAGI to $129,000-plus — one dollar over the second IRMAA cliff. The question is not whether $9,000 of conversion is good tax policy. It is whether $9,000 of conversion is worth a $1,591 Medicare surcharge two years from now.

This page lays out every single-filer IRMAA bracket for 2026, the exact dollar jump at each cliff, and how to set a Roth-conversion ceiling that stops just short of the line you do not want to cross.

The 2026 single-filer IRMAA brackets

IRMAA — the Income-Related Monthly Adjustment Amount — is a surcharge added to your Medicare Part B and Part D premiums when your income exceeds set thresholds. It is authorized under the Medicare Modernization Act and administered by the Social Security Administration (42 U.S.C. §1395r). The base 2026 Part B premium is $185.00/month. Above each MAGI line, you pay that base plus a surcharge.

The annual column is the total cost — twelve months of the full Part B premium plus the Part D surcharge — not just the amount over base. A sub-$103,000 single filer pays $2,220/year (Part B only, no Part D surcharge); a tier-2 filer pays $3,272; a tier-3 filer pays $4,864. The jump between tiers is what the planning is about: $3,272 to $4,864 is roughly $1,591 more a year, the same figure you reach by annualizing the +$132.60/month combined increase. Figures reflect CMS 2026 Medicare premium tiers under the Income-Related Monthly Adjustment Amount rules (42 U.S.C. §1395r(i)); the Part D surcharge is added to whatever your standalone Part D or Medicare Advantage drug plan already charges.

Why the second cliff at $129,000 matters most to converters

The first cliff at $103,000 catches almost every middle-income retiree with a pension and Social Security. But the second cliff — $129,000 — is the one that traps Roth converters, because it is exactly where “fill the 22% bracket” advice tends to land a single filer. The 22% federal bracket for a single filer runs to $103,350 of taxable income in 2026; after the $15,750 standard deduction (plus the $1,600 age-65 addition), a retiree filling that bracket sits at roughly $120,000–$130,000 of MAGI. That is precisely the $129,000 IRMAA line.

Here is the arithmetic of crossing it, from tier 2 to tier 3:

• Part B: $259 → $370 = +$111.00/month
• Part D surcharge: $13.70 → $35.30 = +$21.60/month
• Combined: +$132.60/month × 12 = $1,591.20/year

For a married couple where both spouses are on Medicare, double it — the surcharge is per person, so crossing the equivalent joint line costs roughly $3,182/year. But this page is about the single filer, where one return drives one premium.

The decision: is Margaret’s $9,000 conversion worth $1,591?

Margaret is at $120,000 MAGI. A $9,000 conversion takes her to $129,000-plus, crossing into tier 3. Run both sides:

The last $100 of Margaret’s conversion carries a 1,613% effective cost once the IRMAA surcharge lands. For a one-off conversion with no large looming RMD, capping at $128,900 is the obvious call: she keeps almost the entire conversion and skips the surcharge entirely.

The answer flips only if her traditional IRA is large enough that future RMDs will force her over $129,000 anyway. If she is sitting on a $900,000 pre-tax IRA, her RMD at 73 (divisor 26.5, about 3.77%) is roughly $34,000 — on top of pension and Social Security, that drags her into tier 3 or higher every single year for the rest of her life. In that case, paying one year of surcharge now to permanently shrink the pre-tax balance can beat decades of recurring IRMAA. The cliff math is a one-year cost; the RMD math is a multi-decade cost. Compare them directly before you cap the conversion.

The two-year lookback: your 2024 return sets your 2026 premium

IRMAA is not based on current income. Social Security uses your MAGI from two years prior. Your 2026 premium is set by your 2024 tax return; the conversion you do in 2026 hits your 2028 premium. This lookback is the single most misunderstood feature of IRMAA, and it cuts two ways:

1. It is already locked for the near term. If you crossed a cliff on your 2024 return, your 2026 premium is set and the only relief is an appeal for a qualifying life-changing event.
2. It is plannable for the future. Every conversion, capital gain, and lump sum you take this year is a known input to a premium two years out. You can model it to the dollar before December 31.

IRMAA MAGI is your adjusted gross income (Form 1040 line 11) plus any tax-exempt interest (line 2a). Municipal-bond interest that escapes income tax still counts toward IRMAA — a trap for retirees who shifted to munis to lower their tax bill and inadvertently kept their IRMAA high.

The marginal cost of crossing each single-filer cliff

Every IRMAA line carries its own “cost of the dollar that crosses it.” Knowing each one tells you which cliffs are worth defending hardest. Here is the per-person annual surcharge increase at each single-filer line:

The middle three cliffs — including the $129,000 line — each cost about $1,591/year for a single dollar. The first cliff is cheaper ($1,052) but catches far more people; the top cliff is the smallest jump. For a single converter living in the $103,000–$161,000 MAGI band, the $129,000 line is where the most planning leverage sits, because it is the cliff most converters can actually choose to stop short of.

What most people miss: the cliff is a tax on the dollar, not the bracket

The most common misconception is that IRMAA works like the income-tax brackets — that only the income above the line gets the higher rate. It does not. IRMAA is a cliff, not a marginal bracket. A single filer at $129,001 pays the exact same $370 Part B premium as a single filer at $160,999. The entire $111/month Part B increase is triggered by one dollar.

That is why the marginal cost of the dollar that crosses the line is absurd: that single dollar of MAGI “costs” $1,591 in surcharge. No income-tax bracket behaves this way. It also means the planning move is precise: you do not aim for $129,000 — you aim for a safety margin below it, typically $2,000–$3,000, to absorb a year-end dividend reclassification, a mutual-fund capital-gains distribution you did not control, or a 1099 correction. Hitting exactly $128,999 and then receiving a surprise $50 fund distribution in late December puts you over.

Levers to stay under the $129,000 line

• Cap the conversion. The cleanest lever. Convert up to your target MAGI ceiling and stop. You can always convert more next year.
• Qualified charitable distribution (QCD). If you are 70½ or older, a QCD (up to $108,000 in 2026, indexed; IRC §408(d)(8)) sends IRA money straight to charity and satisfies your RMD without adding a cent to MAGI — the single most powerful IRMAA-management tool for charitably inclined retirees.
• Tax-loss harvesting. Realized capital losses offset realized gains dollar-for-dollar and reduce AGI, pulling MAGI back below the line.
• Time lump sums across tax years. A property sale, a large distribution, or a deferred-comp payout can sometimes be split across two Decembers/Januaries to keep any single year under a tier.
• Watch tax-exempt interest. Muni interest counts for IRMAA even though it escapes income tax. If you are near a cliff, a taxable-account muni-heavy allocation can quietly push you over.

How a QCD beats a Roth conversion for IRMAA-sensitive RMD years

Once Margaret reaches RMD age — 73 if she was born 1951–1959, or 75 if born 1960 or later under SECURE 2.0 §107 — the math changes again. Say her $900,000 IRA at 73 forces a $34,000 RMD (the Uniform Lifetime Table divisor at 73 is 26.5, about 3.77% of the prior year-end balance, per IRS Pub. 590-B Table III). That $34,000 lands on top of her $80,000 of pension and taxable Social Security and pushes her clean over the $129,000 line every year. If she is charitably inclined, a qualified charitable distribution is the one lever that satisfies the RMD without adding a dollar to MAGI: she can send up to $108,000 in 2026 (the indexed limit under IRC §408(d)(8), available from age 70½) straight from the IRA to a 501(c)(3). A $34,000 QCD covers her entire RMD, keeps her MAGI near $108,000 — comfortably under the $129,000 cliff — and saves the full $1,591 surcharge while funding gifts she would have made from her checking account anyway. A Roth conversion does the opposite: it raises MAGI on purpose. The two tools point in opposite directions, and the right one depends on whether her goal that year is shrinking the pre-tax balance (convert) or just clearing the RMD without IRMAA damage (QCD).

The safety-margin discipline matters most in these RMD years because the RMD itself is only known to the dollar after the December 31 prior-year balance is struck. A market rally in the fourth quarter can lift next year’s RMD by thousands and silently widen the gap to the cliff. Building in a $2,000–$3,000 cushion — targeting roughly $126,000–$127,000 of MAGI rather than $128,999 — absorbs that uncertainty plus any year-end mutual-fund capital-gains distribution, dividend reclassification, or 1099 correction you do not control. The cost of the cushion is trivial (a few thousand dollars of conversion deferred to January); the cost of blowing the cliff is the full $1,591.

If you already crossed a cliff because of a one-time event

If your 2024 MAGI spiked from a one-time event — the sale of a business, a large severance, the death of a spouse changing your filing status, or retirement itself — you can appeal. File Form SSA-44 (“Medicare Income-Related Monthly Adjustment Amount — Life-Changing Event”) to ask Social Security to use a more recent, lower income year. Qualifying events include work stoppage or reduction, marriage, divorce, death of a spouse, loss of pension, and loss of income-producing property. A Roth conversion is not a life-changing event — you chose it — so SSA-44 will not unwind a conversion-driven cliff. That is exactly why converters model the cliff in advance rather than appeal after.

The decision lever

Set your Roth-conversion ceiling at the IRMAA tier you do not want to cross, minus a $2,000–$3,000 cushion — for a single filer guarding the second cliff, that means a MAGI target near $126,000–$127,000. Convert up to that ceiling every year you can, fill the rest of the 22% bracket the following January if needed, and only blow through the $129,000 line in years where shrinking a large pre-tax balance ahead of RMDs at 73 or 75 saves more than the $1,591 one-year surcharge costs. The cliff is fixed and knowable two years ahead; build the ceiling into your December conversion math, not your April surprise.