Complex Trusts: DNI, the 65-Day Rule, and Form 1041

A complex trust is taxed as its own entity on any income it retains, at sharply compressed brackets that reach 37% above $16,000 of taxable income for 2026, while income it distributes is deducted at the trust level and taxed instead on the beneficiary’s return, keeping its original character along the way. That basic split, along with a concept called distributable net income, drives almost every decision a trustee makes. The tax treatment and distribution rules for a complex trust exist to prevent double taxation of the same dollar and to discourage using a trust as a tax shelter for accumulated wealth.

What Makes a Trust Complex

The Internal Revenue Code doesn’t define “complex trust” affirmatively. A trust is complex by default if it isn’t a simple trust or a grantor trust. A trust qualifies as simple only when it must distribute all income currently, makes no charitable contributions, and never distributes principal. If the governing document permits any one of three features, the trust is complex.

The first is the authority to accumulate income rather than pay it all out each year. The second is the power to distribute principal (sometimes called corpus), not just the income earned on trust assets. The third is authority to make charitable contributions from gross income. The permission alone is enough; the trustee doesn’t have to exercise it in a given year for the trust to be treated as complex.

Why Keeping Income in the Trust Is Expensive

Trust brackets are compressed on purpose. Where an individual doesn’t reach the top 37% rate until income runs into the hundreds of thousands, a complex trust gets there at $16,000. The full 2026 schedule:¹

10% on taxable income up to $3,300
24% from $3,301 to $11,700
35% from $11,701 to $16,000
37% over $16,000

There is no 12% or 22% bracket. A trust that retains $16,000 of taxable income already owes $3,851, and every additional dollar is taxed at 37%.

Layered on top is the 3.8% Net Investment Income Tax. For a trust, the NIIT threshold is the same dollar figure where the top income tax bracket starts, so for 2026 it kicks in at $16,000 of adjusted gross income. The tax applies to the lesser of the trust’s undistributed net investment income or its AGI above that threshold.² Net investment income includes interest, dividends, capital gains, rents, and royalties. Wages and active trade or business income are excluded.

Stacked together, the top marginal rate on retained investment income can reach 40.8%. Push the same dollar out to a beneficiary in a lower bracket and both the ordinary tax hit and the surtax at the trust level go away. The beneficiary may owe NIIT on their own return, but only if their personal income clears the much higher individual thresholds. That gap is the reason distribution planning dominates complex trust administration.

Distributable Net Income: The Rule That Ties It Together

Distributable net income, or DNI, is the mechanism that keeps trust taxation coherent. DNI does two things at once: it caps the deduction the trust can claim for distributions, and it caps the amount the beneficiary must report as income.³ Without it, a trust could inflate deductions by labeling principal distributions as income, or the same dollar could be taxed twice.

The calculation starts with taxable income and adjusts. Tax-exempt interest is added back because it’s real money available for distribution. The personal exemption is added back too. Capital gains are generally excluded, so they stay trapped inside the trust and get taxed at the entity level.

Within DNI, the conduit principle governs character. Income passing through the trust to a beneficiary keeps whatever tax character it had when the trust received it. Tax-exempt municipal bond interest stays tax-exempt. Qualified dividends keep their preferential rate. Ordinary interest stays ordinary. The trust is a pipeline, not a blender.

When a distribution exceeds DNI, the excess is treated as a tax-free return of principal. The beneficiary owes nothing on the excess, and the trust gets no deduction beyond the DNI cap.

Capital Gains Usually Stay Inside the Trust

The default rule keeps capital gains out of DNI and taxes them at the trust level, where the 20% long-term rate hits at just $16,000 of income, plus the 3.8% NIIT on top. Treasury regulations create three exceptions. Capital gains can be pulled into DNI if they are allocated to income under the trust instrument or state law, allocated to principal but consistently treated on the trust’s books as part of a distribution to a beneficiary, or allocated to principal but actually distributed or used to determine the amount distributed.⁴ A trustee can’t simply decide on this year’s return to include gains in DNI. The treatment has to be authorized by the governing document and applied consistently.

The 65-Day Rule

Section 663(b) gives a trustee a second chance to shift income out of the trust after the year ends. Distributions made within the first 65 days of the new tax year can be treated as if made on the last day of the prior year.⁵ For a calendar-year trust, that window closes March 6.

The election is valuable because year-end income figures aren’t usually known until well after December 31. Rather than guessing in November how much to distribute, the trustee can wait until the accountant produces final numbers, then make a distribution in January or February that lands against the prior year’s DNI. The election must be made affirmatively on page 3 of Form 1041, and it is irrevocable for that year. Filing an extension doesn’t push the 65-day deadline; the money still has to leave the trust within 65 days of year-end, even though the election itself can be made on the extended return.

A separate election under Section 643(g) lets the trustee treat estimated tax payments made by the trust as if paid by the beneficiaries.⁶ It also has to be made within 65 days of year-end. This helps when the trust plans to distribute most of its income anyway, because the beneficiaries pick up the credit on their individual returns.

Whether a distribution is mandatory or discretionary follows the language of the trust instrument. Mandatory distributions come out first when the trust computes its income distribution deduction, and the ordering can matter when multiple beneficiaries receive different types of payments.

Form 1041, K-1s, and Estimated Payments

A complex trust files Form 1041 for any year it has taxable income or gross income of $600 or more, or any beneficiary who is a nonresident alien.⁷ For a calendar-year trust, the return is due April 15, with a 5½-month extension available on Form 7004.⁸ The extension buys time to file, not time to pay.

Each beneficiary who receives a distribution gets a Schedule K-1 breaking down income by category: ordinary dividends, qualified dividends, interest, short- and long-term capital gains, rental income, and so on.⁹ Beneficiaries pick up those figures on Form 1040, and each category retains its character. Qualified dividends still get capital gains rates in the beneficiary’s hands. Tax-exempt interest is reported for information only.

K-1s must be furnished by the Form 1041 filing deadline, including extensions. When a trustee extends, beneficiaries often can’t finalize their own returns until close to October and end up extending as well.

A complex trust expecting to owe $1,000 or more must make quarterly estimated payments. The 2026 due dates for calendar-year trusts are April 15, June 15, September 15, and January 15, 2027.¹ The January payment can be skipped if the trust files by January 31, 2027, and pays the full balance with the return. To avoid an underpayment penalty, the trust must pay the lesser of 90% of the current year’s tax or 100% of the prior year’s (110% if prior-year AGI topped $150,000).¹⁰

What Happens When the Trust Terminates

Winding down a complex trust triggers a set of one-time rules that push certain tax attributes out to the beneficiaries who receive the remaining property.

Unused capital loss carryovers pass through in the year of termination and keep their character. Long-term losses stay long-term, short-term stays short-term, and beneficiaries report them on Schedule D.¹¹ Net operating loss carryovers pass through under the same framework.

Excess deductions on termination arise when deductions (other than the charitable deduction and the personal exemption) exceed gross income in the final year. Those excess deductions flow to beneficiaries on the K-1. A beneficiary who lacks enough income that year to absorb the deduction simply loses it. There is no carryforward.⁹ That makes the timing of termination a real planning decision: closing the trust during a beneficiary’s high-income year captures the value, while closing during a low-income year can waste it.

One further limit applies. Miscellaneous itemized deductions that would have been subject to the 2% AGI floor remain nondeductible under the current suspension. Only deductions qualifying as Section 67(e) expenses or non-miscellaneous itemized deductions pass through as usable deductions to the beneficiary.⁹

1
Internal Revenue Service. 2026 Form 1041-ES – Estimated Income Tax for Estates and Trusts
2
Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax
3
Office of the Law Revision Counsel. 26 USC 661 – Deduction for Estates and Trusts Accumulating Income or Distributing Corpus
4
eCFR. 26 CFR 1.643(a)-3 – Capital Gains and Losses
5
Office of the Law Revision Counsel. 26 USC 663 – Special Rules Applicable to Sections 661 and 662
6
Office of the Law Revision Counsel. 26 USC 643 – Definitions Applicable to Subparts A, B, C, and D
7
Internal Revenue Service. Instructions for Form 1041 and Schedules A, B, G, J, and K-1
8
Internal Revenue Service. Form 7004 Due Dates PY2026
9
Internal Revenue Service. Instructions for Schedule K-1 (Form 1041) for a Beneficiary Filing Form 1040 or 1040-SR
10
Internal Revenue Service. 20.1.3 Estimated Tax Penalties
11
eCFR. 26 CFR 1.642(h)-1 – Unused Loss Carryovers on Termination of an Estate or Trust