Friday's conversion took 22.5 years to pay back. This one takes 4.4.

This article first appeared in The Nest Egg, my daily email, on 2026-09-22. Read the original issue. It is educational, not a recommendation for you. The household in it is a hypothetical example, and market figures are as of the date shown and will have changed.

Every figure below names its document. Every calculation is shown. Nothing here is a forecast.

Good morning. All four stock indexes finished higher yesterday, the Nasdaq 100 closed above 30,000 on a 2.83% day, and crude fell 4.51% to $95.78. Then the conversion we set up yesterday, run on a household that finally has room to do it.

In today's issue

The tape. The Nasdaq 100 gained 2.83% and the S&P 1.49%. WTI crude gave back 4.51% and the 10-year fell 4.3 basis points to 4.953%. Two minutes.

$90,962 of room is really $73,400. Social Security eats $17,562 of the bracket before the first converted dollar is taxed at 12%. Four minutes.

4.44 years. On Friday the same idea took 22.55 years to pay back. Most of the difference is one Medicare line, and the margin is $523.25. Three minutes.

One more thing. Why $60,000 would have been close to the worst amount to convert. One minute.

The tape

Closing levels and session changes, CNBC US markets, September 21, 2026. Gold and WTI crude are front-month futures settlements, measured against the September 18 settlements.

The story

Yesterday's swap moved $1,600,000 out of a taxable ladder and into municipals, and the couple's taxable income fell from $107,400 to $9,838. The planner's point at the end was that the swap opened $90,962 of room under the top of the 12% bracket, where on Friday there was none.

That room is where the most common advice in retirement planning lives: convert while the brackets are low. On Friday that advice failed. We priced a $75,100 conversion on the taxable household at 22%, and it took 22.55 years to pay for itself against the survivor's bill.

Today we run the same idea on the household after the swap. Two things are different, and both matter more than the bracket.

The room is smaller than it looks. And the survivor's Medicare income sits just past a line.

The position

The same household, sixth day in a row.

$1,600,000 in a national municipal ladder at 3.33%, paying $53,280 of tax-exempt interest. $1,200,000 in a traditional IRA. Social Security of $44,000 on his record and $30,000 on hers. Both are 73. As a couple: provisional income $90,280, taxable Social Security $45,338, adjusted gross income $45,338, taxable income $9,838, federal tax $983.80.

Now the survivor, once required distributions begin at 75 and before any conversion.

$1,200,000 divided by the Uniform Lifetime Table divisor of 24.6 is a required distribution of $48,780.49. Her $44,000 benefit is fully 85% taxed at $37,400. Adjusted gross income $86,180.49. Taxable income $68,030.49, inside the 22% single bracket. Income tax $9,678.71.

Her Medicare income adds the $53,280 of municipal interest back, as Monday's letter showed it must: $139,460.49. That is $2,460.49 past the $137,000 single line, which puts her in the second surcharge tier. $202.90 a month for Part B and $37.50 for Part D, or $240.40 a month and $2,884.80 a year. One tier lower is $95.70 a month, or $1,148.40 a year.

Her bill in that year: $9,678.71 + $2,884.80 = $12,563.51.

The arithmetic

Step one. Why $90,962 is really $73,400.

A converted dollar is ordinary income, and ordinary income counts in the Social Security formula. Until the benefit reaches its 85% cap, every converted dollar drags another $0.85 of Social Security into taxable income behind it. Each dollar converted raises taxable income by $1.85.

The couple's benefit reaches the cap at a conversion of $20,661.18. By then taxable Social Security has risen from $45,338 to $62,900, which is $17,562 more. That $17,562 is room under the 12% bracket top that the conversion never gets to use.

So the true fill is smaller. Taxable income reaches the $100,800 top of the 12% bracket at a conversion of $73,400: $73,400 + $62,900 − $35,500 = $100,800.

Step two. What each slice costs.

The first $8,087.57 lands in the 10% bracket, $1.85 at a time: 18.50%, or $1,496.20. The next $12,573.61 lands in the 12% bracket, still $1.85 at a time: 22.20%, or $2,791.34. Together the first $20,661.18 costs $4,287.54, a blended 20.75%.

Then the drag stops. The next $52,738.82 is taxed at exactly 12.00%: $6,328.66.

Total: $73,400 converted for $10,616.20, an effective rate of 14.46%. The couple's tax goes from $983.80 to $11,600.00. Their Medicare income that year, $136,300 of adjusted gross income plus $53,280 of municipal interest, lands at $189,580, well under the $218,000 joint line. No surcharge on the conversion.

The rate climbs from 18.5% to 22.2% and then falls to 12%. The most expensive dollars are the first ones.

Step three. What she saves.

The IRA falls to $1,126,600, so her required distribution at 75 falls to $45,796.75. That is $2,983.74 less income every year.

Income tax: $2,983.74 at 22% is $656.42.

Medicare income: $139,460.49 minus $2,983.74 is $136,476.75, which is $523.25 under the $137,000 line. She drops a tier, and $2,884.80 becomes $1,148.40. That is $1,736.40.

Total: $2,392.82 a year.

Step four. The payback.

$10,616.20 divided by $2,392.82 is 4.44 years.

Friday's formula on the income tax alone: 0.1446 divided by (0.22 divided by 24.6) = 16.17 years. That is already better than Friday's 22.55, because the conversion costs 14.46% instead of 22%.

The Medicare tier does the rest. $1,736.40 of the $2,392.82, or 72.6%, comes from crossing one line.

2026 rates per Revenue Procedure 2025-32 and the 2026 CMS income-related monthly adjustment amounts. Survivor year uses the Uniform Lifetime Table divisor of 24.6 at age 75. Balances held flat. No state tax. Hypothetical illustration of published rates, built to show arithmetic. Not a projection of any reader's result and not a recommendation.

What the four of them would say

The portfolio manager. The swap and the conversion are one decision, not two. Friday's conversion failed because $80,000 of taxable interest had already used up the cheap brackets. Monday's swap, judged alone, cost $14,651.80 a year in after-tax cash and lost. Today it is the reason a conversion costs 14.46% instead of 22%. Judge them separately and both look wrong.

The CPA. The 18.5% and the 22.2% appear on no bracket table anywhere. They appear on the Social Security worksheet, where the taxable amount moves every time the conversion does. A conversion planned from the bracket chart alone is planned from the wrong page.

The financial planner. The number that matters here is not the bracket top. It is $60,528, the smallest conversion that clears the Medicare line in her survivor year. Below it the payback is close to 17 years. Above it, close to 4. And notice when the saving arrives: while both are alive and taking distributions, the conversion saves the couple only $358.05 a year, because they sit in the 12% bracket. The payoff is a survivor's payoff.

The estate attorney. Qualified Roth distributions are excluded from gross income under section 408A(d)(1). They never touch her Medicare income, and they never touch a beneficiary's either. The $73,400 moved today is money that will not set anyone's surcharge again.

One more thing

Why $60,000 would have been close to the worst amount to convert.

It is round, it sits comfortably below the bracket top, and it feels like a sensible middle. It costs $9,008.20. It lowers her Medicare income to $137,021.46, which is $21.46 over the line. She stays in the second tier and saves only $536.59 a year. Payback: 16.79 years.

Convert $60,529 instead. That is $529 more, costing $63.48 more in tax, and it puts her Medicare income $0.04 under the line. Payback: 3.98 years.

Twelve years of payback live inside $529 of conversion. That is what a cliff looks like when you measure it.

Tomorrow

Every number this week has held balances flat, and today's answer rests on a margin of $523.25. Tomorrow we let the IRA grow for the two years before her first required distribution, and find out how much growth that margin can survive.

Sources

2026 brackets, standard deduction and the additional deduction at 65 or older: Revenue Procedure 2025-32. Taxation of Social Security benefits: 26 U.S.C. 86. Roth conversions and qualified distributions: 26 U.S.C. 408A. Uniform Lifetime Table divisors: IRS Publication 590-B, Appendix B. 2026 Part B and Part D income-related monthly adjustment amounts: Centers for Medicare & Medicaid Services. The Medicare surcharge income definition: 42 U.S.C. 1395r(i)(4). Municipal yield and market levels, close of September 21, 2026: CNBC US markets.

The conversation a portfolio manager, a CPA, a financial planner and an estate attorney would have about your money if the four of them were ever in the same room. None of them ever talk to each other. This is that room, every weekday at 6:45am, sized to a portfolio between $500,000 and $5,000,000.

The Nest Egg is educational material published by a registered representative. It is not tax, legal or investment advice, and it is not an offer or solicitation. Every case shown is a hypothetical illustration of published rates, built to demonstrate arithmetic, and is not a projection of any reader's result. State taxes, itemized deductions and the character of investment income are not modeled here and change the result. Nothing here is a recommendation of any security. Consult your own tax and legal advisors before acting.