2027 IRS limits are projected to rise — here's what that means for Roth conversions.

If you're planning a Roth conversion before year-end, the number that matters most — the top of your tax bracket — will change in January. But the IRS won't publish the official 2027 figures until this fall (last year it released the 2026 brackets on October 9 and the 2026 retirement-plan limits on November 13), so for now, everything about 2027 is a projection. Here's what the two best-known projections say, what the difference is worth in dollars, and what it doesn't change.

What's projected for the 2027 401(k) and retirement-plan limits?

Milliman's September 11, 2026 forecast puts the 2027 employee deferral limit at $25,500, up $1,000 from the 2026 limit the IRS confirmed in Notice 2025-67.

2026 figures are from IRS Notice 2025-67; 2027 figures are Milliman's forecast, which assumes the trailing 12-month CPI-U of 3.4% through August 31, 2026 plus a 0.25% rise in September. There's one catch: if September's CPI (released October 14) rises by less than 0.04%, Milliman says the deferral limit would grow only $500, to $25,000, and the catch-up would stay at $8,000.

What's projected for the 2027 tax brackets?

Bloomberg Tax projects the brackets rising roughly 3.2% for 2027 — larger than the 2.7% adjustment from 2025 to 2026. For anyone who fills the 24% bracket with conversions, the number to watch is where that bracket ends:

2026 figures are from IRS Revenue Procedure 2025-32. The extra room comes at the same 24% rate, so converting all of it would cost 24% × $6,550 = $1,572 (single) or 24% × $13,100 = $3,144 (joint) in federal income tax. Bracket tops apply to taxable income — what's left after your deduction — not to gross income.

Does the extra bracket room make a Roth conversion worth it?

Not by itself. The extra room only makes a conversion cheaper to fit inside the 24% bracket; whether converting pays off still comes down to whether your tax rate at withdrawal ends up higher than the rate you pay now, the one rule laid out in when a Roth conversion actually pays off. To put dollars on it, here's the extra room run through the same formula that powers Runway's free Roth conversion calculator:

That advantage depends entirely on the 32%-at-withdrawal assumption. If your rate in retirement ends up at or below 24%, converting is a wash at 24% and a loss below it — which is exactly what the calculator is for. The outside-savings row comes out higher because the full amount lands in the Roth; why that works is covered in the same guide.

A conversion also raises your modified adjusted gross income (MAGI), which has costs the tax bracket doesn't show: Medicare's IRMAA surcharges, which look back two years (see how IRMAA can outweigh the 2027 Social Security raise), and, before 65, the ACA subsidy cliff (see the early retiree's guide). Either can cost more than the income tax on the conversion itself.

Can you use the 2027 brackets for a conversion you do in 2026?

No. Income you recognize in 2026 — including a Roth conversion done in December — is taxed under 2026 brackets, whatever the 2027 numbers turn out to be. If you're sizing a 2026 conversion, the top of the 24% bracket is $201,775 (single) or $403,550 (joint) of taxable income; the projected 2027 figures become usable for conversions you do starting January 1, and only once the IRS confirms them.

How were these numbers calculated?

• 2026 limits and brackets: IRS Notice 2025-67 and Revenue Procedure 2025-32, linked above. These are official.
• 2027 limits and brackets: third-party projections (Milliman, September 11, 2026; Bloomberg Tax). None are official, and this page will be updated when the IRS publishes the real figures.
• Extra bracket room and tax at 24%: straight arithmetic on the figures above.
• The illustration: computed with the formula behind Runway's free Roth conversion calculator, using flat rates, with the stated growth and time assumptions. It ignores state income tax, IRMAA, ACA subsidies, and RMD timing, any of which can change a real answer.