How are ISOs and NQSOs taxed when I move between Canada and the US?

A stock option exercised after a cross-border move is taxed by both countries. The US and Canada each have their own rules for how much of the spread is income and what rate it’s taxed at, the treaty has its own formula for splitting the income between them, and neither country’s foreign tax credit perfectly offsets the other’s claim. The central complication is that Canada does not recognize the US distinction between incentive stock options (ISOs) and non-qualified stock options (NQSOs). All employee stock options in Canada are taxed under ITA section 7, and qualifying options get a 50% deduction under ITA 110(1)(d) that has no US parallel. That mismatch is where the double tax lives.

How does the US tax stock options?

Two regimes, depending on the option type. ISOs (IRC 421/422) produce no ordinary income at exercise if holding periods are met (one year from exercise, two from grant), but the spread is an AMT preference under IRC 56(b)(3). A disqualifying disposition collapses ISO treatment into ordinary income. NQSOs (IRC 83) produce ordinary compensation income at exercise, reported on the W-2 and subject to FICA.

	ISO (holding periods met)	ISO (disqualifying disposition)	NQSO
At exercise	No regular income; AMT preference	Ordinary income on the spread (or gain, if less)	Ordinary income on the spread
On sale	Long-term capital gain	Capital gain on any excess above the ordinary income portion	Capital gain on any excess above FMV at exercise
Employer deduction	None	Yes, matching the employee’s ordinary income (IRC 83(h))	Yes, matching the employee’s ordinary income
Withholding	None at exercise	Supplemental wage rates	Supplemental wage rates

How does Canada tax stock options?

One regime for all options. ITA 7(1)(a) includes in employment income a benefit equal to fair market value at exercise minus the exercise price. For non-CCPC employers the benefit is taxable at exercise; for CCPCs, ITA 7(1.1) defers to the year of disposition. The 50% deduction under ITA 110(1)(d) applies when the exercise price was at or above FMV at grant, halving the effective rate.

• The 2021 amendments cap the 110(1)(d) deduction at $200,000 in annual vesting FMV for non-CCPC employers.
• Canada does not distinguish ISOs from NQSOs. An ISO exercised after a move to Canada is taxed identically to an NQSO. The IRC 422 holding periods and AMT treatment do not carry over.

How does the treaty split the income between countries?

The treaty’s allocation rule is in Annex B, paragraph 6 of the Diplomatic Notes to the Fifth Protocol. Each country’s share equals the days between grant and exercise when the employee’s principal employment was in that country, divided by total days of employment between grant and exercise.

This differs from domestic sourcing. The IRS’s default under Treas. Reg. 1.861-4(b)(2)(i) uses grant-to-vest, not grant-to-exercise. The CRA also defaults to the vesting period. The treaty formula prevails for treaty purposes.

• The distinction matters most when the employee relocates after vesting but before exercise. Under the treaty formula, every day on vested options in the new country shifts the allocation.

Paragraph 6(b) gives the competent authorities a discretionary override for options that were in-the-money at grant or not subject to a substantial vesting period. In those cases, both competent authorities must agree before a different attribution applies.

Where does the double tax come from?

The 110(1)(d) deduction. Canada includes only 50% of the benefit in taxable income, while the US taxes its allocated share at full ordinary rates (up to 37%). The Canadian FTC for US tax paid is limited to Canadian tax on the US-source portion, but that Canadian tax is computed on only half the benefit. If the US tax exceeds the Canadian tax on 50% of the same amount, the excess has no credit to absorb it.

Working the hypothetical above:

• US taxes $120,000 at, say, 32% effective = $38,400 US tax
• Canada taxes $80,000 (the Canadian-allocated portion), but after the 110(1)(d) deduction, only $40,000 is included in taxable income. At a 50% combined marginal rate, Canadian tax on the option is $20,000
• The Canadian FTC for US tax paid is limited to the Canadian tax otherwise payable on the US-source income. The Canadian tax on the US-allocated portion ($120,000, but only $60,000 included after deduction, at 50%) is $30,000
• The US tax of $38,400 exceeds $30,000, leaving $8,400 of US tax unrelieved

That $8,400 is the structural double tax. It exists because Canada taxes at half rate (via the deduction) while the US taxes at full ordinary income rates, and the FTC mechanism can’t bridge the gap.

What about RSUs?

RSUs are a different instrument. The Annex B paragraph 6 formula applies only to options, not RSUs. The CRA applies a separate “Hybrid Methodology” (Technical Interpretation 2019-0832211I7), splitting the benefit into an in-the-money portion sourced to the grant-year jurisdiction and an appreciation portion sourced by days worked during vesting.

• The RSU guide covers that analysis: cross-border RSUs and the W-2/T4 double-tax problem.

Does exercise timing matter?

It’s the single biggest lever. The treaty allocation runs from grant to exercise, so every day the options sit unexercised in the new country shifts the fraction.

• Exercise before the move: only one country claims the income. Simplest path but requires liquidity for tax and (for NQSOs) withholding.
• Exercise immediately after the move: minimizes the new country’s share. Three years in the US plus one month in Canada gives the US roughly 97%.
• Wait years after the move: the new country’s share grows daily. Whether this helps depends on the rate differential and FTC math.
• ISO holding periods add a layer: selling shares less than one year from exercise or two years from grant triggers a disqualifying disposition.

What does Canada do with a non-resident exercise?

If you moved from Canada to the US and exercise as a US resident, Canada still taxes the Canadian-allocated portion. ITA 115(1)(a)(i) includes in a non-resident’s taxable income the employment income earned in Canada. The CRA allocates the benefit using the treaty formula, taking the lower of the domestic and treaty amounts.

• The employer withholds Canadian tax on the Canadian-allocated portion. If the employer is a non-resident without Canadian payroll, the employee may need to remit directly through installments or on the return.

What forms are involved?

US side: the NQSO spread appears on the W-2 (Boxes 1, 3, 5, and Box 12 Code V). Form 1116 claims the FTC for Canadian tax paid. For ISOs, Form 3921 is informational and AMT goes on Form 6251. Canadian side: the benefit goes on the T4 (Box 38 benefit, Box 39 deduction), and Form T2209 claims the FTC for US tax paid.

• No separate treaty form exists. The allocation is computed within the FTC calculations on Form 1116 (US) and T2209 (Canada).
• If the employer is a non-resident without local payroll in either country, the employee may need to self-report the income and remit directly.

What should I do next?

If you’re approaching a move with unvested or unexercised options, the exercise timing decision drives the tax outcome. Model the treaty allocation under different exercise dates and compare FTC capacity under each scenario.

• For RSUs: cross-border RSUs and the W-2/T4 double-tax problem
• For ESPPs: does the US still tax my ESPP after I move to Canada
• For the move itself: moving back to Canada from the US or leaving Canada for the US
• For the AMT exposure on an ISO exercise: alternative minimum tax (AMT) cross-border
• For employer-managed relocations: tax equalization on cross-border corporate moves
• For cash-based deferrals (NQDC, 409A plans): deferred compensation cross-border

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.