What Is a Trust Filing as an Estate Under Sec. 645?

A Section 645 election lets the trustee of a qualified revocable trust and the executor of the related estate treat the trust as part of the estate for income tax purposes, filing one combined Form 1041 instead of two separate returns. The election is made on IRS Form 8855, attached to the estate’s first income tax return, and once made it cannot be revoked.¹ Its value is in the estate-only tax rules it opens up to the trust during administration: a fiscal year, a $600 exemption, a two-year pass on estimated taxes, and several others.

What the Election Does

When the grantor of a revocable trust dies, the trust becomes irrevocable and starts functioning as its own taxable entity. Without the election, the executor files Form 1041 for the estate and the trustee files a separate Form 1041 for the trust. Two returns, two sets of professional fees, and two separate pools of income and deductions that can’t offset each other.

The election collapses the two entities into one for federal income tax purposes. The trust is treated and taxed as part of the estate for the entire election period, and all income, deductions, and credits flow onto a single Form 1041 filed under the estate’s name and taxpayer identification number.¹ Because the choice is irrevocable, both fiduciaries should model the expected tax picture before signing off.

Which Trusts Qualify

The trust must be a qualified revocable trust, meaning the decedent was treated as the owner during life because they held the power to revoke it. In tax terms, that is a trust falling under Section 676 of the tax code, which treats the grantor as owner of any trust they can revoke.² The standard revocable living trust set up for probate avoidance qualifies in almost every case.

A trust that was already irrevocable at the decedent’s death does not qualify, even if it held most of the decedent’s assets. If only a portion of a trust was revocable, only that portion is eligible.

Who Files It and How

If the estate has a court-appointed executor, both the executor and the trustee must agree to the election; neither can force it on the other. The executor then files the combined Form 1041 under the estate’s name and EIN, and the return picks up all items from both the estate and the electing trust.³

Many revocable trust plans are designed to avoid probate, so no executor is ever appointed. In that situation the trustee can make the election alone. The trustee files Form 1041 as if the trust were an estate, using the TIN obtained for the trust after the death, and gets the same fiscal year flexibility and $600 exemption an estate would receive.³

The election itself is made on Form 8855, Election to Treat a Qualified Revocable Trust as Part of an Estate.⁴ The form collects the decedent’s name and Social Security number along with the names, addresses, and employer identification numbers for both the estate and the trust. If either entity lacks an EIN, get one before filing.

Form 8855 is not filed on its own. It must be attached to the first Form 1041 filed for the estate, or the first Form 1041 filed by the trustee acting as the estate when there is no executor. The deadline is the due date of that first return, including extensions.⁵ Miss it and the election is gone permanently. No late-filing relief is available, so putting the first Form 1041 on extension early is a simple way to buy time.

What the Election Gains You

The combined filing is not just about convenience. Several rules that normally apply only to estates become available to the trust during the election period, and some of them save real money.

Fiscal Year Flexibility

Trusts are locked into a calendar tax year by statute.⁶ Estates can pick any fiscal year-end. Under the election, the trust follows the estate’s fiscal year. A decedent who died in November, for example, can end up with a January 31 fiscal year-end that pushes most of the first year’s income into a return not due until the following May. That creates room to gather brokerage statements, rental income records, and K-1s before filing.

With the right year-end, the entire administration sometimes fits into a single Form 1041, which reduces professional fees. The fiscal year is set on the first Form 1041, so run projected numbers before picking it.

Higher Personal Exemption

An estate takes a $600 personal exemption on Form 1041. A trust required to distribute all of its income gets $300, and every other trust gets $100.⁷ The dollar difference is small, but during the election period the higher figure comes with the return you were filing anyway.

No Estimated Tax for Up to Two Years

Estates are not required to make estimated tax payments during any tax year ending within two years of the decedent’s death.⁸ Without the election, the trust has to begin quarterly estimated payments immediately, even while the estate itself is exempt. The election extends the estate’s exemption to the trust, eliminating underpayment penalty risk during a period when income is hard to predict and liquid cash may be tied up.

Rental Real Estate Losses

If the decedent actively managed rental properties before death, the estate can deduct up to $25,000 in passive rental real estate losses against other income during the two tax years following death.⁹ That allowance normally does not extend to trusts. Under the election, the trust rides on the estate’s active participation status and can claim those losses.¹⁰ For decedents who held rental real estate generating paper losses through depreciation, this benefit alone can justify making the election.

S Corporation Stock

An estate is an eligible shareholder of an S corporation for the duration of administration. A regular irrevocable trust has to fit one of the narrow categories (such as an electing small business trust or a qualified subchapter S trust) to hold S corporation stock without breaking the company’s S election.¹¹ During the Section 645 election period the trust is treated as part of the estate for S corporation purposes, keeping the stock in safe harbor without restructuring or a rushed distribution.¹² Once the election ends, the trustee needs a plan for the stock.

Charitable Set-Aside Deduction

Estates can deduct amounts permanently set aside for charity under the governing instrument, even before the money is actually paid out.¹³ Trusts created after 1969 generally cannot take this set-aside deduction; they only get to deduct charitable amounts actually distributed during the year. Under the election, a revocable trust with charitable provisions gains access to the estate’s set-aside rule during the election period. That matters most when the instrument directs income to be held for eventual charitable distribution rather than paid out immediately.

How Long the Election Lasts

The election period runs from the date of death to the “applicable date,” which depends on whether the estate is large enough to owe a federal estate tax return (Form 706).¹

If no Form 706 is required, the election ends two years after the date of death. For 2026 deaths, Form 706 is required only when the gross estate exceeds $15,000,000, so most estates fall into this category.¹⁴
If Form 706 is required, the election ends six months after the final determination of the estate tax liability, or two years after the date of death, whichever is later. Estate tax audits and litigation can push the final determination date out considerably.

The election also ends early if both the estate and the electing trust have distributed all their assets before the applicable date. Once everything is distributed there is nothing left to tax on a combined return.¹²

What Happens When It Ends

When the election period terminates, the trust stops being treated as part of the estate and returns to its own taxable existence. If the trust still holds assets and will continue operating, several things have to happen at once.

The trust may need a new taxpayer identification number. If there was an executor, a new TIN may be required. If there was no executor and the trustee had been filing under a TIN obtained after the decedent’s death, the trust must obtain a new one.¹⁵ The estate, if it continues, keeps its original TIN.

The trust also loses its fiscal year. Since trusts must use a calendar year, the trust’s first post-election return covers the short period from the day after the election ends through December 31. After that, the trustee files calendar-year Forms 1041 annually for as long as the trust holds assets or earns income.

All the other estate-only benefits disappear at the same time. Estimated tax payments start, the exemption drops to $100 or $300, the $25,000 rental real estate allowance goes away, and any S corporation stock still in the trust must be held under a qualifying structure or distributed. Planning for that transition well before the election period expires is worth the effort, especially with S corporation stock or rental properties in the mix.

1
Office of the Law Revision Counsel. 26 U.S.C. 645 – Certain Revocable Trusts Treated as Part of Estate
2
Office of the Law Revision Counsel. 26 U.S.C. 676 – Power to Revoke
3
Internal Revenue Service. Instructions for Form 1041 and Schedules A, B, G, J, and K-1 (2025)
4
Internal Revenue Service. About Form 8855, Election to Treat a Qualified Revocable Trust as Part of an Estate
5
Internal Revenue Service. Form 8855 (Rev. December 2020) Election to Treat a Qualified Revocable Trust as Part of an Estate
6
GovInfo. 26 U.S.C. 644 – Taxable Year of Trusts
7
Internal Revenue Service. Instructions for Form 1041 and Schedules A, B, G, J, and K-1 (2025) – Section: Line 21—Exemption
8
Office of the Law Revision Counsel. 26 U.S.C. 6654 – Failure by Individual to Pay Estimated Income Tax
9
Office of the Law Revision Counsel. 26 U.S.C. 469 – Passive Activity Losses and Credits Limited
10
Internal Revenue Service. Publication 925, Passive Activity and At-Risk Rules
11
eCFR. 26 CFR 1.1361-1 – S Corporation Defined
12
eCFR. 26 CFR 1.645-1 – Election by Certain Revocable Trusts to Be Treated as Part of Estate
13
Office of the Law Revision Counsel. 26 U.S.C. 642 – Special Rules for Credits and Deductions
14
Internal Revenue Service. What’s New — Estate and Gift Tax
15
GovInfo. 26 CFR 1.645-1 – Election to Treat Trust as Part of an Estate