Specialized Returns and Taxpayers · Trust and estate income tax
Filing requirements, tax years, and penalties
tax year · reviewed 2026-08-21 · Draft for I. Ohu review
Three separate returns can arise on a death and they are easily confused: the decedent’s final income tax return, the fiduciary income tax return of the estate, and the estate tax return. Each has its own trigger, its own threshold and its own deadline, and one of the three is required far less often than clients expect.
The rule
Who files a fiduciary income tax return. an estate files where its gross income for the taxable year is $600 or moreTY2026 (IRC § 6012(a)(3)) and a trust files where it has any taxable income for the year, or gross income of $600 or more regardless of the amount of taxable incomeTY2026 (IRC § 6012(a)(4)). Note the asymmetry — a trust files on any taxable income however small, an estate only at the threshold. And one trigger ignores amounts entirely: an estate or trust any of whose beneficiaries is a non-resident alien must file regardless of income — the one trigger that has nothing to do with amountsTY2026 (IRC § 6012(a)(5)).
A grantor trust files nothing of its own. where the grantor or another person is treated as the owner of a portion of a trust, the items of income, deduction and credit attributable to that portion are included in computing that person’s taxable income and credits, to the extent they would be taken into account for an individual — the remaining portion staying subject to the ordinary subchapter J rulesTY2026 (IRC § 671) puts the items on the owner’s return, and the trust reports through an alternative method rather than by computing tax.
The taxable year. the taxable year of any trust is the calendar year, except a trust exempt under IRC § 501(a) or described in IRC § 4947(a)(1) — while an estate may adopt any fiscal year ending within twelve months of deathTY2026 (IRC § 644). This is the largest practical difference between an estate and a trust in administration.
And the election that combines them. where the executor of an estate and the trustee of a qualified revocable trust both elect, the trust is treated and taxed as part of the estate rather than as a separate trust, for all taxable years of the estate ending after the date of death and before the applicable dateTY2026 (IRC § 645(a)).
Deadlines. A fiduciary return is due the 15th day of the fourth month following the close of the taxable year (IRC § 6072(a)), with an extension available under IRC § 6081 — five and a half months for a Form 1041, not the six months a corporation gets.
Estimated tax. the estimated tax rules do not apply, for any taxable year ending before the date 2 years after the date of death, to the decedent’s estate or to a trust all of which was treated as owned by the decedent and which received the residue under the will — or, where there is no will, which is primarily responsible for paying debts, taxes and administration expensesTY2026 (IRC § 6654(l)(2)), and outside that window IRC § 6654(l)(1) applies the estimated tax rules to estates and trusts generally.
Penalties. IRC § 6651 imposes the failure to file and failure to pay additions in the ordinary way; there is no per-beneficiary penalty of the kind IRC §§ 6698 and 6699 impose on partnerships and S corporations.
Current figures
| Item | Rule | Authority |
|---|---|---|
| Estate filing | an estate files where its gross income for the taxable year is $600 or moreTY2026 | IRC § 6012(a)(3) |
| Trust filing | a trust files where it has any taxable income for the year, or gross income of $600 or more regardless of the amount of taxable incomeTY2026 | IRC § 6012(a)(4) |
| Non-resident alien beneficiary | an estate or trust any of whose beneficiaries is a non-resident alien must file regardless of income — the one trigger that has nothing to do with amountsTY2026 | IRC § 6012(a)(5) |
| Taxable year | the taxable year of any trust is the calendar year, except a trust exempt under IRC § 501(a) or described in IRC § 4947(a)(1) — while an estate may adopt any fiscal year ending within twelve months of deathTY2026 | IRC § 644 |
| Section 645 election | where the executor of an estate and the trustee of a qualified revocable trust both elect, the trust is treated and taxed as part of the estate rather than as a separate trust, for all taxable years of the estate ending after the date of death and before the applicable dateTY2026 | IRC § 645(a) |
| Estimated tax exemption | the estimated tax rules do not apply, for any taxable year ending before the date 2 years after the date of death, to the decedent’s estate or to a trust all of which was treated as owned by the decedent and which received the residue under the will — or, where there is no will, which is primarily responsible for paying debts, taxes and administration expensesTY2026 | IRC § 6654(l)(2) |
| Grantor trust | where the grantor or another person is treated as the owner of a portion of a trust, the items of income, deduction and credit attributable to that portion are included in computing that person’s taxable income and credits, to the extent they would be taken into account for an individual — the remaining portion staying subject to the ordinary subchapter J rulesTY2026 | IRC § 671 |
How it works in practice
Keep the three returns apart. The decedent’s final Form 1040 covers income to the date of death and is required on the ordinary individual thresholds. The estate’s Form 1041 covers income the estate earns afterwards and is required only where an estate files where its gross income for the taxable year is $600 or moreTY2026. The Form 706 estate tax return is required only where the gross estate plus adjusted taxable gifts exceeds the basic exclusion amount, which for most estates it does not. A small estate with a modest income routinely needs only the first.
Use the fiscal year. A trust must use the calendar year under IRC § 644, but an estate may adopt any fiscal year ending within twelve months of the date of death. Choosing a year end shortly before the first anniversary defers the beneficiaries’ inclusion of distributions into their following tax year, and lets administration expenses fall in the period that suits. It is the largest planning lever available and it is exercised simply by filing the first return on that basis.
The IRC § 645 election exports the fiscal year to the trust. A funded revocable trust, which would otherwise be a separate taxpayer on the calendar year the moment the grantor dies, can elect with the executor to be treated and taxed as part of the estate — so it shares the estate’s fiscal year, its single exemption and its estimated tax exemption. It runs until the applicable date, which depends on whether a Form 706 is required.
Remember the estimated tax holiday. IRC § 6654(l)(2) disapplies estimated tax for any taxable year ending before the date two years after death, for the estate and for a trust all of which was treated as owned by the decedent and which received the residue. That is a genuine deferral of payment, not merely of filing, and it interacts with the fiscal year choice.
Watch the non-resident alien trigger. IRC § 6012(a)(5) requires a return where any beneficiary is a non-resident alien, with no income threshold at all. A trust with no income and one foreign beneficiary files; a trust with income below the threshold and only domestic beneficiaries does not.
Note what does not exist here. There is no penalty measured by the number of beneficiaries. IRC § 6651 applies in the ordinary way, so the exposure on a late fiduciary return is a percentage of the tax due — which on a trust that distributed everything may be nothing at all. That is a material difference from the partnership and S corporation regimes and explains why late fiduciary returns are more common.
Scenarios
The estate that needed one return
An individual dies leaving a gross estate of $6,500,000, well below the basic exclusion amount. The estate earns $400 of interest during administration before the assets are distributed.
Only the final Form 1040 is required. IRC § 6012(a)(3) requires a fiduciary income tax return from an estate whose gross income for the taxable year is $600 or more, and $400 is below it. The Form 706 estate tax return is required only where the gross estate plus adjusted taxable gifts exceeds the basic exclusion amount, which this estate does not approach.
The decedent’s final individual return is required on the ordinary individual thresholds and covers income to the date of death. Two of the three returns fall away — and note that the estate might still choose to file a Form 1041 to start the assessment period running, which is a different question from whether it must.
The fiscal year that moved a year of tax
A decedent dies on 20 March. The estate will earn substantial income and expects to make its distributions in the following spring. The executor adopts a fiscal year ending 28 February.
The choice does real work. IRC § 644 would force a calendar year on a trust, but an estate may adopt any fiscal year ending within twelve months of death, so the first return covers 20 March to 28 February. Distributions made in that period carry distributable net income to the beneficiaries in the estate’s year ending 28 February — which the beneficiaries include in their own calendar year in which the estate’s year ends, deferring their tax by up to eleven months.
Two further benefits follow. Administration expenses can be placed in whichever fiscal period suits, and IRC § 6654(l)(2) exempts the estate from estimated tax for years ending before the second anniversary of death — which on this fiscal year covers the first two returns entirely.
The revocable trust that joined the estate
A decedent’s assets were held in a funded revocable trust, so probate is minimal and the estate holds almost nothing. The trust becomes irrevocable on death and would otherwise be a separate taxpayer on the calendar year.
The trustee and the executor elect under IRC § 645. The trust is then treated and taxed as part of the estate rather than as a separate trust for all taxable years of the estate ending after the date of death and before the applicable date — so it shares the estate’s fiscal year, files on the estate’s return, uses the estate’s $600 exemption rather than the trust’s $100, and takes the benefit of the IRC § 6654(l)(2) estimated tax exemption.
Without the election the trust would file its own calendar-year return from the date of death, lose the fiscal year deferral entirely, take the smaller exemption, and be subject to estimated tax. For an estate plan built around a revocable trust — which most now are — this is the single most valuable election available in the first two years.
Traps
A trust files on any taxable income; an estate only at the threshold. a trust files where it has any taxable income for the year, or gross income of $600 or more regardless of the amount of taxable incomeTY2026, while IRC § 6012(a)(3) applies only the gross income threshold to an estate.
A non-resident alien beneficiary triggers filing regardless of income. IRC § 6012(a)(5) has no threshold, so a trust with no income at all files if any beneficiary is a non-resident alien.
Only an estate may choose a fiscal year. IRC § 644 requires a trust to use the calendar year, with narrow exceptions for exempt and charitable trusts. The IRC § 645 election is the only route by which a revocable trust reaches a fiscal year.
The Form 1041 extension is five and a half months, not six. The general IRC § 6081(a) power is limited to six months, but the extension granted for a fiduciary return is shorter — which puts the extended deadline before, not on, the date preparers expect.
How this has changed
The requirement that trusts use the calendar year came in with the Tax Reform Act of 1986 and closed what had been a substantial deferral: a trust on a fiscal year could push a beneficiary’s inclusion almost a year forward, and multiple trusts with staggered year ends could compound it. Estates were left alone because administration genuinely takes an unpredictable period, and that asymmetry is what the fiscal year planning now rests on.
The IRC § 645 election was added in 1997 to answer a problem the 1986 change created. As revocable trusts replaced probate as the ordinary way of holding assets at death, the estate that could use a fiscal year often held nothing while the trust that held everything could not. The election restores parity between an estate plan built on a will and one built on a trust, and it is now routine rather than exceptional.
The thresholds themselves have not moved. The gross income figure in IRC § 6012(a)(3) and (4) is the same figure that appears as the estate’s exemption in IRC § 642(b)(1), dates from 1954, and is not indexed. Nothing in the post-2024 legislation alters any of the provisions on this page.
Exam focus
Know the three filing triggers separately, and in particular that a trust’s threshold is any taxable income while an estate’s is the gross income figure, and that the non-resident alien beneficiary trigger has no threshold at all.
Know that a trust uses the calendar year under IRC § 644 and that an estate may choose any fiscal year ending within twelve months of death. Expect a question that turns on this asymmetry.
Know what the IRC § 645 election does — a qualified revocable trust treated and taxed as part of the estate, sharing the fiscal year, the exemption and the estimated tax exemption — and that both the executor and the trustee must elect.
Know the estimated tax exemption in IRC § 6654(l)(2) by its measure: taxable years ending before the date two years after death.
Finally, keep the three post-death returns distinct and know which threshold governs each.
Check yourself
1. A trust has gross income of $450 and taxable income of $120 after its exemption and expenses. Must it file?
Answer: Yes. IRC § 6012(a)(4) requires a return from every trust having any taxable income for the taxable year, or gross income of $600 or over regardless of the amount of taxable income. The gross income limb is not met, but the taxable income limb is — $120 is taxable income and the statute sets no minimum. An estate in the same position would not file, because IRC § 6012(a)(3) applies only the $600 gross income threshold. The asymmetry is deliberate and frequently tested.
2. A decedent dies on 5 September. May the estate adopt a fiscal year ending 31 August, and could the decedent’s revocable trust do the same?
Answer: The estate may — an estate may adopt any fiscal year ending within twelve months of the date of death, and 31 August of the following year is within that period. The trust may not on its own: IRC § 644(a) requires the taxable year of any trust to be the calendar year, with exceptions only for trusts exempt under IRC § 501(a) and trusts described in § 4947(a)(1). The trust reaches the estate’s fiscal year only through an IRC § 645 election, which requires both the executor and the trustee to elect.
3. An estate earns $30,000 in its first taxable year, ending fourteen months after death. Is it liable for estimated tax?
Answer: For the part of the year falling before the second anniversary of death, no — but note the premise is wrong. An estate’s first taxable year cannot exceed twelve months, so a year ending fourteen months after death is not available. Assuming a year ending within twelve months, IRC § 6654(l)(2) disapplies the estimated tax rules to the estate for any taxable year ending before the date two years after death, so the first and usually the second fiscal year are exempt entirely. From the first year ending after that date, IRC § 6654(l)(1) applies the estimated tax rules in the ordinary way.
4. A trust has no income at all for the year. One of its four beneficiaries is a non-resident alien. Must it file?
Answer: Yes. IRC § 6012(a)(5) requires a return from every estate or trust of which any beneficiary is a non-resident alien, and imposes no income threshold. The absence of income is irrelevant. This is the only one of the three fiduciary filing triggers that turns on a fact about the beneficiaries rather than on amounts, and it is easy to miss because it sits in a separate paragraph from the two that do.
5. Why is the IRC § 645 election more valuable now than when it was enacted?
Answer: Because the estate planning pattern it accommodates has become the norm. When trusts were forced onto the calendar year in 1986, most decedents’ assets passed through probate to an estate that could choose a fiscal year. As funded revocable trusts replaced probate, the entity that could use a fiscal year — the estate — often held almost nothing, while the entity holding everything was locked to the calendar year and to the $100 exemption. IRC § 645 lets the trust be treated and taxed as part of the estate, restoring the fiscal year, the larger exemption and the estimated tax exemption to the assets that actually generate the income.
Change log
- Initial draft. Sets out the three IRC § 6012(a) filing triggers for estates and trusts including the non-resident alien beneficiary trigger that ignores amounts, the IRC § 644 requirement that a trust use the calendar year against an estate's freedom to choose a fiscal year, the IRC § 645 election to treat a qualified revocable trust as part of the estate, and the IRC § 6654(l)(2) exemption from estimated tax for the first two years after death.