In short
Dates, rates and thresholds for a property sale between October and December 2026: estimated tax, capital gains bands, NIIT, IRMAA tiers and the 180-day trap.
This edition covers sales that close between October 1 and December 31, 2026, using figures published as of September 30, 2026. A fourth-quarter seller faces three dates (October 15, January 15 and the April 15 return deadline that can cut a 180-day exchange short), four tax thresholds that set the rate on the gain, and a Medicare premium surcharge that shows up two years later. The 2027 figures are not out yet; we say below when they usually arrive.
The dates that matter this quarter
- October 15, 2026. Extended 2025 returns are due. The IRS reminded extension filers of this date in IR-2026-101. If you sold in 2025 and are still reporting the exchange, Form 8824 goes with this return; see how to fill out Form 8824.
- January 15, 2027. The fourth 2026 estimated tax payment is due, per the 2026 Form 1040-ES. You can skip it if you file your 2026 return by February 1, 2027 and pay the full balance with it.
- April 15, 2027, and the 180-day trap. Under section 1031(a)(3), replacement property must be received by the earlier of day 180 or the due date, with extensions, of your return for the year you sold. A sale on October 17, 2026 reaches day 180 on April 15, 2027. Any later 2026 closing loses days unless you extend your 2026 return. The tax extension answer and the year-end deadlines guide walk through it.
The IRS interest rate on unpaid individual tax stays at 7% for the quarter that began October 1, 2026, compounded daily, under Rev. Rul. 2026-15 (IR-2026-98).
Estimated tax when a sale lands late in the year
The 1040-ES general rule asks for estimated payments if you expect to owe at least $1,000 after withholding and your withholding falls short of the smaller of 90% of your 2026 tax or 100% of your 2025 tax. If your 2025 adjusted gross income was over $150,000 ($75,000 married filing separately), the second test becomes 110% of your 2025 tax. That prior-year safe harbor is the simple route for a seller whose 2026 gain is a one-off: pay enough by January 15 to reach 110% of last year’s tax and the underpayment penalty does not apply, even if the sale makes this year’s tax much larger.
A large gain late in the year can also be handled with the annualized income installment method, which the 1040-ES instructions point to when income changes after March 31; it requires Form 2210 with Schedule AI. If you complete an exchange, there may be little or no gain to estimate. If you might not, plan for the tax now rather than in April.
The 2026 thresholds that price the gain
From section 4.03 of Rev. Proc. 2025-32, long-term capital gain is taxed at:
| Filing status | 0% up to | 15% up to | 20% above |
|---|---|---|---|
| Married filing jointly | $98,900 | $613,700 | $613,700 |
| Single | $49,450 | $545,500 | $545,500 |
| Head of household | $66,200 | $579,600 | $579,600 |
| Estates and trusts | $3,300 | $16,250 | $16,250 |
Two layers sit on top and are not indexed. Unrecaptured section 1250 gain, the depreciation you took on the building, is taxed at up to 25% under section 1(h). The 3.8% net investment income tax in section 1411 applies above modified adjusted gross income of $250,000 joint, $200,000 single and $125,000 married filing separately. The 2026 tax numbers page has the full set, and the 20% threshold page explains the top band.
IRMAA: the 2026 sale that raises your 2028 Medicare premiums
Medicare Part B and Part D premiums rise with income. The 2026 tiers below, published by CMS on November 14, 2025, are based on 2024 modified adjusted gross income, according to the Social Security Administration’s POMS HI 01101.020. So a gain realised in 2026 feeds the 2028 premium year.
| Joint MAGI (single) | Part B per person per month | Part D add-on |
|---|---|---|
| Up to $218,000 ($109,000) | $202.90 | $0 |
| Up to $274,000 ($137,000) | $284.10 | $14.50 |
| Up to $342,000 ($171,000) | $405.80 | $37.50 |
| Up to $410,000 ($205,000) | $527.50 | $60.40 |
| Under $750,000 ($500,000) | $649.20 | $83.30 |
| $750,000 or more ($500,000 or more) | $689.90 | $91.00 |
You can ask Social Security to use a more recent year only after a listed life-changing event. POMS HI 01120.005 names “voluntary sale of income-producing property” as an event that does not qualify. A planned sale is exactly that.
A hypothetical fourth-quarter sale
A married couple, both on Medicare, has $120,000 of other income and sells a rental in November 2026 for a $400,000 long-term gain. Their modified adjusted gross income becomes about $520,000.
- Net investment income tax: 3.8% of $270,000 (the amount over $250,000) is $10,260.
- Medicare, two years later: if the 2028 tiers matched the 2026 table, they would land in the “under $750,000” row. Part B would cost $446.30 more per person per month than the standard $202.90, or $10,711.20 a year for the couple, plus $1,999.20 of Part D add-ons.
- If the sale is a completed exchange with no boot, the gain is deferred, their income stays near $120,000, and neither charge applies that year.
The 2028 tiers will be different; this only shows scale. Run your own numbers with your CPA.
When the 2027 numbers arrive
The IRS released the 2026 brackets on October 9, 2025 in IR-2025-103; the 2027 release had not appeared by September 30, 2026. CMS published the 2026 premiums and IRMAA tiers in mid-November 2025. Our 2027 inflation adjustments post lists what will move, and the next edition of this series will carry the new figures.
What to do now
- If your closing could fall after October 17, decide now whether you will extend your 2026 return to protect the full 180 days.
- Ask your CPA to compare your January 15 payment against 110% of your 2025 tax, with and without a completed exchange.
- If you are 63 or older, include the two-year Medicare lookback in the sell-or-exchange model; the NIIT answer covers the other surcharge.
- If you need a replacement that can close before year end, request a proposal.
Sources
- IR-2026-101, extension filers and the October 15 deadline
- IRS, 2026 Form 1040-ES, Estimated Tax for Individuals
- 26 U.S.C. section 1031
- IR-2026-98, interest rates for the fourth quarter of 2026
- Rev. Proc. 2025-32, section 4.03
- 26 U.S.C. section 1
- 26 U.S.C. section 1411
- CMS, 2026 Medicare Parts A and B premiums and deductibles
- SSA POMS HI 01101.020, IRMAA sliding scale tables
- SSA POMS HI 01120.005, life-changing events
- IR-2025-103, 2026 inflation adjustments
