Write three columns: calendar year, MAGI that year, Medicare year it prices. 2026 MAGI prices 2028 premiums. 2024 MAGI is already pricing 2026 — you cannot unwind that with a conversion you have not done yet. If you enroll in Part B in 2027, 2025 is the return SSA will open. Do not convert this year because the market is down until you know which premium year you are buying. Put both spouses on the same page if either will be 65 in that window.
Pull MAGI from the last 1040, not from a feeling. Line 11 (AGI) plus line 2a (tax-exempt interest). That is SSA POMS HI 01101.010. Wages, pension, taxable Social Security, IRA/401(k) withdrawals, conversions, capital gains, rental, Schedule C. Municipal interest is the silent add. Roth basis withdrawals and a QCD are the silent subtracts. If you cannot point at last year’s return, you cannot run the rest of this file.
Name the premium year you actually care about — enrollment, not a slogan. Medicare is 65 (or 24 months of SSDI). Claiming Social Security is a different calendar; delaying the check does not delay Part B if you are not covered by current-employer insurance. Missing Part B is a late-enrollment penalty that IRMAA does not unwind. If nobody in the household is within two years of Part B, this file is a dry run and the ACA MAGI cliff (this year, not +2) may be the one that bites instead.
Stack MAGI from the bottom, then the residual is the conversion. Wages or pension. Taxable Social Security (up to 85%). Planned RMDs — run the RMD calculator; do not guess the factor. Capital gains you cannot defer (installment close, 1099-B already in). Then the conversion or extra sale you actually want. Subtract HSA / 401(k) deferrals if you are still eligible. The leftover under the next CMS floor is the room. If the leftover is $8,000, convert $8,000 — not $30,000 to get it over with.
Run the MAGI-room tool before you call the custodian. Prefill is the worked slice: single, $50k + $28k + $22k = $100,000 MAGI, first 2026 floor $109,000, room $9,000. Add $10,000 extra → $110,000 → first surcharge $81.20 Part B + $14.50 Part D = $95.70/mo × 12 = $1,148.40 for one enrollee, $2,296.80 for two. Copy the share URL into this file. The 2026 table is a stand-in for 2028 floors — they will be higher; staying $9k under today’s floor is extra margin, not a lock.
Price the conversion’s income tax in the other calculator. Do not rebuild it here. Extra federal vs remaining 12/22/24% room, NIIT flag, state % — that is /tools/roth-conversion.html and the primer fill 12% or 22%. This step is only the join: if all-in (tax + IRMAA two years later) on the last dollars over the cliff is worse than waiting a year, wait. Multi-year conversions almost always beat one spike once IRMAA and NIIT are in the model. Pay the conversion tax from cash, not from the IRA.
QCD first, before a taxable IRA withdrawal, if you give anyway. Age 70½+, IRA only, trustee-to-charity, 2026 exclusion $111,000 (Notice 2025-67). Counts toward the RMD. Never hits MAGI. Taking the RMD to checking in June and donating in December already booked the cliff. You cannot QCD from a 401(k). Sequence with the RMD playbook — this page owns the MAGI reason, that page owns the table and the 10-year inherited clock.
Capital gains are a calendar, not a mood. Specific-ID the high-basis lots in an IRMAA window. Harvest losses against the rest in the same year. Delay a December close to January if that one sale is the dollar that crosses $109k / $218k — you buy twelve months of cheaper Part B. A primary-residence exclusion (IRC 121) still leaves gain above $250k / $500k in MAGI; that is how a house sale prices two years of IRMAA and is not a listed SSA-44 event. Do not cash-out a cheap mortgage to “simplify” into a cliff — housing file is HELOC vs cash-out, not this page.
SSA-44 only when the event is listed, with evidence. Work stoppage, work reduction, marriage, divorce/annulment, death of a spouse, loss of income-producing property, loss of pension income, employer settlement. Print the last paystub / termination letter / death certificate into the file. A one-time capital-gain year and a Roth conversion are not on the list. If you retired in May 2026, 2026 MAGI (partial W-2) may already be the right number for 2028; file the form when SSA still prices 2024’s full W-2 on 2026 premiums. New initial determination, not a “please undo my conversion” letter.
Household math: two enrollees, and the MFS trap. Each person on Part B/D pays their own surcharge. First-cliff extra is $95.70/mo each — a couple both enrolled pays $2,296.80/year for the first CMS 2026 tier. Married filing separately who lived together jump from $0 to the 80% tier above $109,000 (Part B $649.20 + Part D $83.30). Lived-apart-all-year can use the single table — prove it. Do not file MFS as a MAGI trick without running both columns in the calculator.
When the SSA letter arrives, compare it to column one — then decide appeal vs pay. IRMAA letters typically show up late in the year before the premium year (fall 2025 for 2026). Check the MAGI SSA used against the 1040 you actually filed. If it is the right year and the right MAGI, paying is the move; the cliff is working as designed. If income dropped because of a listed event, SSA-44. If SSA used a three-year-old return because IRS lagged, a new-initial-determination with the later 1040 can reprice. Do not ignore the letter until January premiums jump — Part D IRMAA is billed by SSA, often withheld from the Social Security check with Part B.
Hard-stop list: converting $250k in one year to “get it over with” and lighting the $274k MFJ cliff ($240.40/mo extra per person at the 2026 second tier); treating the $109k / $218k floors as 2028 law; filing SSA-44 for a brokerage sale; taking the RMD to checking then QCD-ing the leftover; delaying the first RMD to April 1 and dumping two RMDs into one MAGI year (see the RMD file); delaying Medicare because you delayed Social Security; filing MFS while living together to “split MAGI”; withholding conversion tax from the IRA so MAGI is the conversion plus the withholding gross-up. If the MAGI tool says you are $2,000 under a cliff, you wanted a smaller conversion, not a bigger slogan. The 12% fill lives in tax-efficient withdrawals. This page is the cliff.
One-page decision
Calendar year → MAGI → premium year +2. Stack the 1040 from the bottom. Convert only the residual under the next CMS floor, priced in the conversion calculator, paid from cash. QCD before the taxable RMD if you give. Delay a December sale to January when that dollar is the cliff. SSA-44 for listed events only. Two enrollees pay twice. November letter, not January surprise. The table is a stand-in. The order of accounts is the other playbook.