Roth Conversion in 2026: Should You Pay the Tax Now?

The 60-second rule

Convert when your retirement tax rate will be higher than today’s — and only with tax money from outside the IRA. That’s the whole game. At the defaults ($100,000, 24% now, 32% later, 20 years, 8%), converting finishes at $466,095.71 of after-tax wealth against $406,406.61 for keeping — a $59,689.10 win. The break-even is 19.19%: any retirement rate above that, and paying 24% now is buying tax-free growth at a discount. Run your own numbers in the Roth conversion calculator — especially the “where does the tax come from” selector, because paying the tax from the converted dollars destroys $111,862.97 of the win. Everything below is the evidence for that rule.

How a Roth conversion really works

You move dollars from a traditional IRA or 401(k) into a Roth IRA and pay ordinary income tax on the converted amount that year — it stacks on top of your other income, so a big conversion can shove you into a higher bracket. From that moment the dollars are Roth dollars: no tax on qualified withdrawals ever again, no required minimum distributions, and your heirs inherit them income-tax-free. The price is the tax bill now, and the IRS gives you no undo button: since the Tax Cuts and Jobs Act, conversions completed after December 31, 2017 cannot be recharacterized — if markets drop 30% the month after you convert, you still owe tax on the pre-drop value. That finality is why advisors preach partial conversions over one big sweep.

The $59,689.10 worked example, line by line

$100,000 converted, 24% marginal rate now, 32% expected in retirement, 20 years, 8% growth, conversion tax paid from a taxable account:

Convert: $100,000 × 1.08²⁰ = $466,095.71 — every dollar yours, forever. The $24,000 tax bill is paid separately from outside funds.

Keep: the same $100,000 grows to $466,095.71 pre-tax, then retirement takes 32% → $316,945.08. But the fair fight doesn’t end there: the unspent $24,000 stays invested in a taxable account, growing at 6.8% (8% minus a disclosed 15%-a-year tax drag) for 20 years → $89,461.52. Total keep-side wealth: $406,406.61.

The gap: converting wins by $59,689.10 — even giving the keep side full credit for the tax money. Now the twist: set both rates to 24% and the textbook calls it a wash — but converting still wins by $22,401.45. That leftover win is the outside-funds bonus: the $24,000 tax payment is economically an extra Roth contribution that compounds tax-free for 20 years. Flip it around — 32% now, 12% later — and keeping wins by $63,350.55. The rate spread decides; the funding source amplifies.

The three windows when converting wins

1. The gap years. The classic window: retired but not yet taking Social Security or RMDs, living off taxable savings in a low bracket. Converting up to the top of the 12% bracket (which ends at $100,800 for joint filers, $50,400 single, in 2026) year after year moves serious money at bargain rates.

2. The low-income year. A sabbatical, a job change, a business loss — any year your marginal rate dips is a conversion sale. The calculator’s break-even rate tells you exactly how low “low” needs to be.

3. The legacy play. Roth dollars pass to heirs income-tax-free with no RMDs forcing distributions during your lifetime. If the goal is the kids’ inheritance rather than your spending, the conversion is estate planning wearing a tax costume — and the math gets even friendlier.

When keeping the traditional account wins

Three situations flip the verdict. One: peak earnings. Converting at 32–37% today to dodge 22% later is paying retail to avoid wholesale — the calculator shows keeping ahead by $63,350.55 in the 32%-now/12%-later case. Two: no outside funds. If the tax has to come from the IRA itself, you’re not converting $100,000 — you’re converting $76,000 and prepaying tax on money you destroyed; the bonus becomes a penalty. Three: the IRMAA trap. A 2026 conversion inflates the MAGI that sets 2028 Medicare premiums — the first surcharge tier starts at $109,000 for single filers — so a “winning” conversion can cost an extra $1,000+ a year in premiums. Size conversions with the two-year lookback on the calendar.

The December 31 deadline (and the custodian problem)

A 2026 conversion counts only if it completes by December 31, 2026 — the tax year is the year the money leaves the traditional account, and there is no April extension. Worse, most custodians set internal processing cutoffs in mid-to-late December: a request submitted December 30 may not post until January, blowing the deadline you were trying to hit. Two more tripwires: the 10% default withholding on Form W-4R — withheld dollars are not converted, and under 59½ they can draw the 10% early-withdrawal penalty on top — and the RMD-first rule: a conversion does not satisfy a required minimum distribution, so take the RMD first; those dollars can’t be converted. And the pro-rata rule: if you hold after-tax dollars alongside pre-tax money across traditional, SEP, or SIMPLE IRAs, every converted dollar is a proportional mix — track basis on Form 8606.

Three mistakes to avoid

1. Paying the tax from the IRA. The single most expensive error: it shrinks the Roth by the tax amount and forfeits the outside-funds bonus — $111,862.97 of tax-free growth at the defaults. Only convert what you can pay tax on from a taxable account.
2. Converting into a higher bracket blind. The conversion stacks on top of your income — spilling into the next bracket taxes the spill at the higher rate. Fill the bracket; don’t flood it. (The 2026 12% ceiling is $100,800 joint / $50,400 single.)
3. Forgetting the two-year clocks. IRMAA looks back two years (2026 income → 2028 premiums), and each conversion starts its own five-year clock for penalty-free access to converted dollars under 59½. The conversion you do at 63 echoes at 65 and 68 — plan all three dates, not just this April’s return.