The Net Investment Income Tax for Americans in Canada: The 3.8% No Foreign Tax Credit Offsets, and the Treaty Argument Over It

The net investment income tax is the one US tax an American in Canada cannot make disappear with the foreign tax credit, and for a high-income expat with a portfolio it is the largest recurring double-tax leak in the corridor. The tax: 3.8% on the lesser of net investment income or the excess of modified adjusted gross income over the threshold — US$200,000 for single filers, US$250,000 for married filing jointly, US$125,000 for married filing separately — with the thresholds unindexed since enactment, so inflation pulls more expats over them every year; net investment income includes interest, dividends, capital gains, rental and royalty income, non-qualified annuity income, and passive business income, less allocable deductions, and excludes wages, self-employment income, distributions from qualified retirement plans and IRAs, Social Security, and tax-exempt interest. For an American in Canada: Canadian salary is not net investment income (it is excluded, and the foreign earned income exclusion or credit handles its regular tax), but the Canadian brokerage account's dividends and interest, the TFSA's income and gains (taxable annually to the US), gains on the sale of Canadian investments, Canadian rental income, and — critically — the modified adjusted gross income that the excluded or credited salary still counts toward (the threshold is measured on MAGI, which adds back the foreign earned income exclusion) all feed the computation; RRSP and RRIF income deferred under the treaty is not currently included, and distributions from RRSPs are pension income excluded from net investment income. Why the credit fails: the foreign tax credit under section 901 is a credit against the taxes imposed by chapter 1 of the Code; the net investment income tax is imposed by section 1411, which sits in chapter 2A — a different chapter — and the statute grants no credit against it; the IRS's position, stated in the regulations and consistently in guidance, is that foreign taxes cannot be credited against the net investment income tax, so the American in Canada pays Canadian tax on the investment income (at Canadian rates, which already exceed US rates) and then 3.8% to the US on the same income with no offset — pure double taxation of the kind the treaty exists to prevent, which is where the argument begins. The treaty position: the Canada-US treaty's double-taxation-relief article obliges the United States to allow a credit for Canadian income tax against United States tax on the same income, in accordance with the provisions and subject to the limitations of US law — and the question is whether the net investment income tax is a United States tax on income to which the treaty's credit obligation applies independently of the Code's chapter-based limitation; practitioners taking the position that it is file Form 8833 disclosing a treaty-based return position that the treaty itself authorizes a credit for Canadian tax against the net investment income tax, compute the credit on a separate Form 1116-style schedule, and claim it — and the position was litigated: the Court of Federal Claims held in Christensen, under the France treaty, that the treaty's own credit provision was not limited by the Code's chapter structure and required a credit against the net investment income tax, while the Tax Court in Toulouse had denied a treaty-based credit — but on August 31, 2026, in the Canadian case Estate of Bruyea, the Federal Circuit reversed a Court of Federal Claims ruling that had allowed a credit and held that the Canada treaty does not provide a credit against the net investment income tax (the France treaty question in Christensen is a separate case that ruling did not resolve), reading the relief article's "subject to the limitations of the law of the United States" to import the Code's chapter-1-only restriction. For the Canada treaty specifically, the argument is now foreclosed at the appellate level; only the Supreme Court could revive it. Where the position stands after Bruyea: an affirmative claim now runs directly against controlling Federal Circuit authority interpreting the Canada treaty, so it is very likely to be denied and to draw the audit the Form 8833 discloses; a taxpayer who still wants to preserve the sliver of upside from a possible Supreme Court reversal does so by paying the tax and filing a protective refund claim within the refund statute, not by claiming the credit on the return — and for most Americans in Canada the treaty credit is no longer a live planning option but a closed question the base-reduction planning has to work around. The planning that shrinks the base regardless of the treaty question: asset location — holding investment assets inside the RRSP (whose income is deferred and excluded) rather than in taxable or TFSA accounts; the TFSA decision (its income is net investment income to the US every year — one more reason Americans in Canada usually skip it); realizing gains in years when MAGI is below the threshold (a sabbatical, a retirement year); the timing of large dispositions against the threshold; installment sales and charitable strategies that spread or remove gains; and the married-filing-jointly threshold for couples where the Canadian spouse is a nonresident alien — the section 6013(g) election to file jointly raises the threshold from US$125,000 (married filing separately) to US$250,000 but brings the Canadian spouse's worldwide income into the US return, a trade the joint-election guide analyzes. The expat's annual NIIT review: compute MAGI with the exclusion added back; compute net investment income from the U.S. and Canadian accounts; apply the lesser-of rule; decide whether to file a protective refund claim against a possible Supreme Court reversal (the affirmative credit having lost at the Federal Circuit); and run the asset-location changes for next year, because the tax is small in rate and large in persistence, and the base is now the only part of it the taxpayer controls at all.

Key takeaways

• The tax: 3.8% on the lesser of net investment income or MAGI over the unindexed thresholds (US$200,000 single, US$250,000 joint, US$125,000 married filing separately) — interest, dividends, gains, rents, and passive income; not wages, retirement plan distributions, Social Security, or treaty-deferred RRSP income.
• The credit fails under the Code: section 901 credits chapter 1 taxes; the NIIT is chapter 2A; the IRS allows no foreign tax credit against it — Canadian tax on the same income offsets nothing.
• The Canada treaty argument is now foreclosed: in Estate of Bruyea v. United States (Fed. Cir., August 31, 2026), the Federal Circuit reversed a Court of Federal Claims ruling that had allowed a credit, holding that the Code allows foreign tax credits only against chapter 1 income taxes — the NIIT sits in chapter 2A — and that the Canada treaty does not independently provide one. The separate question under the France treaty (Christensen) is not resolved by that ruling. Absent Supreme Court review, the credit is off the table for Americans in Canada.
• Only a protective claim remains: with the appellate court now against the credit for the Canada treaty, an affirmative Form 8833 claim runs against controlling authority; the most a cautious filer does is pay the tax and file a protective refund claim in case the Supreme Court revisits it.
• The base is the controllable part: asset location into the RRSP, skipping the TFSA, timing gains against low-MAGI years, and the joint-election threshold trade for mixed couples.
• MAGI adds back the exclusion: Canadian salary excluded under the FEIE still counts toward the threshold — a common surprise for expats who thought the exclusion made them low-income for US purposes.

The annual NIIT review

MAGI computed with the foreign earned income exclusion added back. Net investment income tallied from every account in both countries (TFSA income included; RRSP income excluded). The lesser-of computation. The treaty decision, now narrow: whether to file a protective refund claim against a possible Supreme Court reversal, deadlines calendared — the affirmative credit having lost at the Federal Circuit for the Canada treaty. The base-reduction plan for next year: what moves into the RRSP, what leaves the TFSA, which gains wait for a lower-MAGI year, whether the joint election changes the threshold. An hour a year, and the tax whose treaty escape hatch the courts just closed.

Worked example

A dual-citizen executive in Toronto earns C$260,000 of salary (credited, not excluded) and holds a C$900,000 taxable portfolio and a C$110,000 TFSA. MAGI: well above US$200,000 as a single filer. Net investment income: about US$38,000 from the portfolio and TFSA (dividends, interest, and realized gains). NIIT: 3.8% of US$38,000 — about US$1,450 — owed on top of the regular US tax that her Canadian tax already fully credits; her Ontario tax on the same investment income was roughly US$18,000, none of which offsets the US$1,450 under the Code. Her decision: because the treaty credit has now lost at the Federal Circuit for the Canada treaty, she pays the NIIT and files a protective refund claim only to preserve the remote chance of a Supreme Court reversal, deadlines calendared — the real money is in the base. Her base reduction: the TFSA is wound down (its C$4,000 of annual income was net investment income with no Canadian tax to even argue about); the portfolio's income-producing holdings are shifted toward her RRSP room over two years; and next year's NIIT is projected at a third of this year's. Her colleague, who filed an affirmative Form 8833 credit in an earlier year before Bruyea came down, now faces the reversal head-on — the credit disallowed, the US$1,450 (plus interest) due — a reminder that the position that looked live in 2024 is closed in 2026.

Official sources

The IRS explains: “The NIIT applies at a rate of 3.8% to certain net investment income of individuals, estates and trusts that have income above the statutory threshold amounts.” — Internal Revenue Service, Questions and answers on the Net Investment Income Tax, https://www.irs.gov/newsroom/questions-and-answers-on-the-net-investment-income-tax

The IRS explains: “If you use Form 1116 to figure the credit, your foreign tax credit will be the smaller of the amount of foreign tax paid or accrued, or the amount of U.S. tax attributable to your foreign source income.” — Internal Revenue Service, Topic no. 856, Foreign tax credit, https://www.irs.gov/taxtopics/tc856

Practitioner note

The net investment income tax is the one double-tax leak the credit machinery can't close, and every high-income American in Canada with a portfolio pays it or argues about it. We explain the treaty position with the actual case outcomes and let the client choose between the affirmative claim and pay-and-protect — then spend the real effort on the base, because moving income into the RRSP and out of the TFSA shrinks the tax regardless of how the courts eventually read the relief article.

See also: For the retire-in-Canada-or-the-US comparison, account by account, see the retire-in-Canada-or-the-US comparison, account by account; and browse every cross-border tax topic guide, organized by situation.

Next step

Fairlight prepares the NIIT engagement — the annual MAGI and net-investment-income computation with the exclusion add-back, the treaty-position decision documented with refund-claim calendaring, and the asset-location and timing plan that reduces the base. See cross-border pricing or book a call.