A Canadian Trust With a US Beneficiary: Form 3520, UNI, and the Throwback Tax That Punishes Waiting

The US taxes beneficiaries of foreign non-grantor trusts on what they receive, but it refuses to let deferral be free. Income a Canadian trust earns and retains becomes undistributed net income — UNI. When a later distribution exceeds the trust's current-year income (DNI), the excess is an accumulation distribution deemed to come from UNI, and the throwback rules tax it as if received in the years the income was earned: at the beneficiary's rates for those years, plus an interest charge running from each of those years to now, and with capital gains stripped of preferential character. A trust that accumulated for fifteen years can hand a US beneficiary a distribution where tax and interest consume a large fraction of it. The reporting spine is Form 3520: the US beneficiary files it for any year with a distribution, and the computation depends entirely on what the trustee can document — a Foreign Nongrantor Trust Beneficiary Statement supporting the actual calculation, or, without one, a default method that assumes accumulation and prices it accordingly.

Key takeaways

• Current distributions are the good case: amounts within the trust's current income are taxed to the beneficiary as ordinary income/qualified dividends per the trust's character, with foreign tax credits for Canadian tax the beneficiary bears — annoying paperwork, normal tax.
• UNI is the ratchet: every year the trust retains income adds to UNI; UNI never expires; capital gains, which Canadian trustees habitually retain, are UNI for this purpose because a foreign trust's gains are in its DNI.
• The interest charge compounds from the year the income was earned — the mechanism that makes old accumulations so expensive and why the age of the UNI matters more than its size.
• Beneficiary statements decide the method: with a timely statement from the trustee, the beneficiary computes actual DNI/UNI amounts; without one, the default method on Form 3520 treats a large share of the distribution as accumulation based on the prior three years' distributions — often worse than reality, sometimes the only option.
• Penalties for silence: an unfiled Form 3520 for a reportable distribution starts at 35% of the distribution — the reporting failure can cost more than the throwback itself.
• Trustee hygiene prevents all of it: distribute income (including gains) currently to US beneficiaries each year; keep separate US-legible accounting of DNI, UNI, and taxes; issue beneficiary statements; avoid PFICs; and where legacy UNI exists, model whether to distribute it deliberately now (stopping the interest clock), restructure, or keep the US beneficiary to current income only.

Where this walks in the door

Almost never as planning — as inheritance. A Canadian family trust settled decades ago has a beneficiary who moved to the US, married an American, or was born American; the trustees have retained gains forever because Canadian tax logic favored it; and now a house down payment is wanted in Austin. The first professional question is not "how much tax" but "what records exist" — reconstructing DNI and UNI year by year from old T3s and statements is what makes the actual method available, and the actual method is usually the saving.

Worked example

A Canadian trust settled by a grandfather in 2010 has retained income and gains of about $500,000 (UNI), earning and retaining roughly $40,000 a year. One of three beneficiaries, a granddaughter in Chicago, is a US citizen; the trustees propose a $250,000 distribution to her. As proposed: current-year DNI allocable to her is small, so most of the $250,000 is an accumulation distribution thrown back across up to fifteen years — prior-year rates plus an interest charge compounding from as far back as 2011, with the gains portion taxed as ordinary income; her Form 3520 runs the actual method only because the trustees can produce full accounts, and the combined federal hit approaches half the accumulation portion. As restructured: the trustees distribute her share of current income every year from now on ($13,000-odd, clean), satisfy the $250,000 need with a distribution structured after modeling — part current income, part deliberate UNI distribution taken now because the interest clock only worsens, part loan from the trust at prescribed terms while the family weighs a broader reorganization — and her 3520s carry beneficiary statements each year. The unfixable part is history: the interest charge on 2011 UNI exists because 2011 income waited; every year of further waiting compounds it.

Official sources

The IRS explains the reporting obligations attached to foreign trusts: a US owner of a foreign trust ensures the trust files Form 3520-A, US persons report transfers to and distributions from foreign trusts on Form 3520, and distributions of accumulated income to US beneficiaries can be subject to the accumulation distribution (throwback) rules with an interest charge. — Internal Revenue Service, Foreign trust reporting requirements and tax consequences, https://www.irs.gov/businesses/international-businesses/foreign-trust-reporting-requirements-and-tax-consequences

U.S. persons file Form 3520 to report certain transactions with foreign trusts, ownership of foreign trusts under the grantor trust rules, and receipt of certain large gifts or bequests from certain foreign persons. — Internal Revenue Service, About Form 3520, https://www.irs.gov/forms-pubs/about-form-3520

Practitioner note

Throwback is the compound-interest version of a filing problem: the tax is annoying, the interest is the killer, and both trace to trustees who ran a Canadian trust on Canadian instincts. The standing instruction we give every trust with a US beneficiary fits on one line — pay their income out every year, and paper it — because UNI prevented is worth ten times UNI managed.

See also: For when a US person as trustee makes a Canadian trust a foreign trust, see when a US person as trustee makes a Canadian trust a foreign trust; and browse every cross-border tax topic guide, organized by situation.

Next step

Fairlight prepares the DNI/UNI reconstruction, the Form 3520 computations under the actual method, and the distribution policy that keeps the trust clean for its US beneficiaries. See cross-border pricing or book a call.