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.

Incentive stock options (ISOs) are governed by IRC 421 and IRC 422. If the holding period requirements are met (shares held at least one year from exercise and two years from grant), no ordinary income is recognized at exercise. The gain is capital gain when the shares are sold. The catch is the alternative minimum tax: IRC 56(b)(3) requires the spread at exercise to be added back as an AMT preference item, so the tax-free treatment at exercise is only “free” for regular tax purposes.

If the holding periods are not met (a “disqualifying disposition”), the spread at exercise (or the gain on sale, whichever is less) becomes ordinary income under IRC 421(b), and the ISO effectively collapses into NQSO treatment.

Non-qualified stock options (NQSOs) are governed by IRC 83. The spread at exercise (fair market value minus exercise price) is ordinary compensation income, reported on the W-2, subject to income tax withholding at 22% (37% over $1 million in supplemental wages per Treas. Reg. 31.3402(g)-1), and subject to FICA. The employee’s basis in the shares becomes the fair market value at exercise, so any subsequent gain or loss on the shares is capital gain or loss.

	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 the fair market value of the shares at exercise minus the exercise price (and minus any amount paid to acquire the option right). For non-CCPC employers (public companies, foreign-controlled corporations), the benefit is taxable in the year of exercise. For Canadian-controlled private corporations, ITA 7(1.1) defers the benefit to the year the employee disposes of the shares.

The 50% stock option deduction under ITA 110(1)(d) is available when the exercise price was at least fair market value at grant and the shares are prescribed shares (arm’s-length dealing). This halves the effective tax rate on the benefit, approximating capital gains treatment.

The 2021 amendments introduced a $200,000 annual vesting limit on the 110(1)(d) deduction for non-CCPC employers. Options whose underlying shares exceed $200,000 in fair market value (measured at grant) that vest in a single year do not get the deduction on the excess.

The important structural point: Canada does not distinguish between ISOs and NQSOs. An ISO exercised after a move to Canada is taxed the same way as an NQSO. The IRC 422 holding period requirements, the AMT preference, the absence of withholding, none of that carries over. Canada sees employment income at exercise, with the 110(1)(d) deduction if the conditions are met.

How does the treaty split the income between countries?

The allocation rule for stock options is in Annex B, paragraph 6 of the Diplomatic Notes to the Fifth Protocol, signed September 21, 2007. It provides a specific formula:

Country X’s share = (days between grant and exercise when the employee’s principal place of employment was in Country X) / (total days between grant and exercise when the employee was employed by the employer)

This is different from how either country sources the income under its own domestic law. The IRS’s default sourcing (under Treas. Reg. 1.861-4(b)(2)(i)) uses the grant-to-vest period, not grant-to-exercise. The CRA, following OECD Commentary paragraphs 12 through 12.15, also defaults to the vesting period for domestic purposes (confirmed in CRA Technical Interpretation 2012-0459411C6). But when the treaty applies, both countries use the treaty’s grant-to-exercise formula, which can produce a very different split.

The distinction matters most when the employee relocates after vesting but before exercise. Under the domestic grant-to-vest rule, the post-vesting period doesn’t change the allocation. Under the treaty’s grant-to-exercise rule, every day the employee sits 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. Here’s the math:

Canada taxes the option benefit but includes only 50% in taxable income (after the deduction). The US taxes its allocated share at ordinary income rates (up to 37%). The Canadian foreign tax credit for US tax paid is limited to the Canadian tax attributable to the US-source portion. But the Canadian tax attributable to that portion is calculated on only 50% of the benefit (because of the deduction). If the US tax on the full US-allocated amount exceeds the Canadian tax on half the same amount, the excess US tax has no Canadian 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 with a different allocation rule. The treaty’s Annex B paragraph 6 stock option formula applies only to options (“an option that was granted … to acquire shares”). RSUs vest and settle into shares without an exercise; they don’t pass through Annex B paragraph 6. The CRA applies a separate methodology for RSUs (the “Hybrid Methodology” introduced in 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. Three scenarios:

Exercise before the move. Only one country is the resident country at the time of exercise. If you exercise while still a US resident, the full spread is US-source ordinary income (for NQSOs) or an AMT preference (for ISOs). Canada has no claim because you’re not yet a Canadian resident. This is the simplest path but requires liquidity to cover the tax and (for NQSOs) the withholding.

Exercise immediately after the move. Minimizes the new country’s share of the treaty allocation. If you spent 3 years in the US and exercise one month after arriving in Canada, the treaty fraction gives the US roughly 97% and Canada roughly 3%.

Wait years after the move to exercise. The new country’s share grows with each passing day. If the options are deeply in the money and you’re in no hurry, waiting increases the Canada-allocated portion, which gets the 110(1)(d) deduction. Whether that’s a net benefit depends on the US vs. Canadian tax rates and the FTC math.

The ISO holding periods add a layer: selling the shares less than one year from exercise or less than two years from grant triggers a disqualifying disposition, converting capital gains to ordinary income. If you exercise ISOs while still in the US and sell after moving to Canada, the holding period timing relative to the move date determines whether the ISO treatment survives.

What does Canada do with the spread if I’m a non-resident exercising?

If you moved from Canada to the US and exercise the options 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 option benefit to the Canadian employment period using the framework in Technical Interpretation 2012-0440741I7, applying the treaty allocation and 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 a Canadian payroll, the withholding obligation is less clear, and the employee may need to remit directly through installments or on the return.

What forms are involved?

US side (for a US resident exercising NQSOs): The spread appears on the W-2 in Boxes 1, 3, and 5, and in Box 12 with Code V. If the employer doesn’t issue a W-2 (foreign employer), the income goes on the 1040 as “other income” and the employee may need to self-report for FICA. Form 1116 claims the foreign tax credit for any Canadian tax paid. For ISOs, no W-2 reporting at exercise (Form 3921 is informational); AMT computation on Form 6251.

Canadian side (for a Canadian resident exercising): The benefit goes on the T4 in Box 38 (stock option security benefit) and Box 39 (110(1)(d) deduction). If the employer is not a Canadian payer, the employee self-reports the benefit on the T1 return. Form T2209 (Federal Foreign Tax Credits) claims the FTC for US tax paid.

Treaty allocation: No separate treaty form. The allocation is computed and applied within the FTC calculations on Form 1116 (US) and T2209 (Canada).

What should I do next?

If you’re approaching a move with unvested or unexercised options, the exercise timing decision is the one that drives the tax outcome. Model the treaty allocation under different exercise dates, compare the FTC capacity under each scenario, and factor in the ISO holding periods if applicable. The interaction between the 110(1)(d) deduction and the US ordinary income treatment is where the planning lives.

For RSUs, the analysis is different: the RSU guide. For ESPPs, which have their own character mismatch between the US discount and Canada’s treatment: does the US still tax my ESPP after I move to Canada. For the broader move itself: moving back to Canada from the US or leaving Canada for the US.

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