Canada’s thin capitalization rules in the Income Tax Act, set out in subsections 18(4) through 18(8), cap how much interest a Canadian-resident corporation or trust can deduct on debt owed to certain foreign shareholders. If that debt exceeds 1.5 times the borrower’s equity, a proportional slice of the interest is denied as a deduction and recharacterized as a dividend paid to the non-resident, which then attracts Part XIII withholding tax. The rules exist because interest reduces Canadian taxable income while dividends do not, so debt is an easy channel for shifting profits offshore.
Who the Rules Apply To
Two categories of Canadian-resident taxpayers fall inside the rules: corporations and trusts carrying debt owed to specified non-residents. Under subsection 18(5), a specified non-resident shareholder is a non-resident person who owns 25% or more of the issued shares of any class of the corporation’s capital stock, counting shares held alone or together with non-arm’s length parties.1Canada Revenue Agency. Income Tax Act Interest on Debts Owing to Specified Non-Residents (Thin Capitalization) The rules also reach any non-resident who does not deal at arm’s length with such a shareholder, even where that person holds no shares.
Canadian-resident trusts face the same framework when they have specified non-resident beneficiaries.2Government of Canada. Income Tax Act – Section 18 The 25% ownership threshold applies whether interests are held directly or indirectly through holding structures.
The 1.5-to-1 Debt-to-Equity Test
The core test compares outstanding debt to specified non-residents against the borrower’s equity amount. If debt exceeds 1.5 times equity, the corporation is thinly capitalized for that tax year.
The debt side captures the greatest amount of interest-bearing obligations owed to specified non-residents at any point during the year. This peak-amount approach means even a brief spike in borrowing can trip the rule, so companies that draw on and repay foreign credit lines need to track daily balances to know their maximum exposure.
How the Equity Amount Is Calculated
For a Canadian-resident corporation, the equity amount under subsection 18(5) has three components:2Government of Canada. Income Tax Act – Section 18
- Retained earnings at the beginning of the tax year, excluding the retained earnings of any other corporation (such as subsidiaries accounted for under the equity method).
- The average of monthly balances of contributed surplus provided by specified non-resident shareholders, including capital contributed beyond the par value of shares.
- The average of monthly balances of paid-up capital for shares owned by specified non-resident shareholders. Shares held by anyone else are excluded.
The monthly averaging matters. A corporation that increases paid-up capital partway through the year picks up partial credit proportional to the months remaining, rather than getting a full-year benefit or nothing at all.
For trusts, the equity calculation starts with the average monthly equity contributions of specified non-resident beneficiaries plus the trust’s tax-paid earnings, then subtracts amounts paid or payable to beneficiaries, with exceptions for amounts already included in a beneficiary’s income or subject to Part XIII tax.2Government of Canada. Income Tax Act – Section 18
How Much Interest Gets Denied
Where debt to specified non-residents exceeds 1.5 times equity, a proportional share of the interest becomes non-deductible. Take the excess debt (total debt minus 1.5 times equity), divide it by total outstanding debt, and multiply the result by the total interest paid or payable to specified non-residents.1Canada Revenue Agency. Income Tax Act Interest on Debts Owing to Specified Non-Residents (Thin Capitalization)
A worked example: a corporation owes $15 million to a specified non-resident and its equity amount is $6 million. Permitted debt is $9 million (1.5 × $6 million). The excess is $6 million. The non-deductible proportion is $6 million ÷ $15 million, or 40%. Forty percent of the interest paid to that non-resident gets added back to taxable income.
Deemed Dividend and Part XIII Withholding
Losing the deduction is only the first hit. Under subsection 214(16), the disallowed interest is recharacterized as a deemed dividend paid to the non-resident lender. It is no longer treated as interest for Part XIII purposes.3Government of Canada. Income Tax Act – Section 214
Canada imposes Part XIII withholding tax on dividends paid to non-residents at 25%.4Canada Revenue Agency. Rates for Part XIII Tax Most bilateral tax treaties reduce this. For major partners such as the United States, the United Kingdom, and many European countries, dividend withholding typically falls between 5% and 15%, depending on the ownership percentage and the treaty terms. Without a treaty, the full 25% applies.
Subsection 214(16)(b) lets the corporation designate which specific interest payments are treated as the deemed dividend, giving some control over the timing of the withholding obligation.3Government of Canada. Income Tax Act – Section 214 The corporation, not the non-resident, is the party responsible for remitting the withholding tax to the CRA. Getting timing or amount wrong invites penalties and compounding interest.
Back-to-Back Loans
Some groups tried to route loans through third-party intermediaries. The foreign parent would deposit funds with a bank, which then lent to the Canadian entity. Because the Canadian company technically owed an arm’s-length bank, the debt would not count under the thin capitalization ratio.
Subsection 18(6.1) closes this off. When an intermediary lends to the Canadian taxpayer and certain conditions are met, the loan is treated as if made directly by the specified non-resident.2Government of Canada. Income Tax Act – Section 18 The conditions look for arrangements where the intermediary’s lending is backed by property provided by the non-resident, where the intermediary’s recourse is limited to the taxpayer’s obligation, or where the intermediary’s loan is conditional on that obligation existing.
When the rules apply, the deemed amount outstanding equals the lesser of what is owed to the intermediary and the fair market value of the pledged property or conditional loan. Interest on that deemed amount then runs through the same thin capitalization calculation as a direct loan. A standalone guarantee, on its own, does not trigger the back-to-back rules.
How EIFEL Interacts with Thin Capitalization
Canada’s Excessive Interest and Financing Expenses Limitation (EIFEL) rules add a separate ceiling on interest deductions. For tax years beginning on or after October 1, 2023, EIFEL applies, and for tax years beginning on or after January 1, 2024, it caps net interest and financing expenses at 30% of adjusted taxable income.5Canada Revenue Agency. Excessive Interest and Financing Expenses Limitation Rules
EIFEL sits alongside thin capitalization; it does not replace it. A corporation can pass the 1.5-to-1 ratio and still have interest denied under EIFEL if net interest exceeds 30% of adjusted taxable income. Several groups are exempt, including Canadian-controlled private corporations with taxable capital under $50 million, entities with aggregate net interest expenses of $1 million or less, and certain standalone Canadian groups with limited ties to non-residents.5Canada Revenue Agency. Excessive Interest and Financing Expenses Limitation Rules Those exemptions focus EIFEL on larger multinational groups, which is roughly the same population most affected by thin capitalization.
Penalties and Filing Exposure
Getting thin capitalization wrong creates exposure on more than one front. The most immediate consequence is reassessment: the CRA adds the disallowed interest to taxable income and assesses the Part XIII withholding tax that should have been remitted on the deemed dividend. The prescribed interest rate on overdue corporate taxes is 7% for Q1 2026, and it compounds daily.6Canada Revenue Agency. Interest Rates for the First Calendar Quarter
Corporations transacting with non-arm’s length non-residents must also file a T106 Information Return.7Canada Revenue Agency. T106 Information Return of Non-Arm’s Length Transactions with Non-Residents The penalties escalate with the nature of the failure:8Canada Revenue Agency. Table of Penalties
- Basic late-filing penalty of $25 per day, to a maximum of $2,500.
- Gross negligence penalty of $500 per month for up to 24 months (maximum $12,000) where the failure is knowing or grossly negligent, less any basic penalties already assessed.
- Failure after demand: $1,000 per month for up to 24 months (maximum $24,000) where the CRA has issued a formal demand and the taxpayer still does not comply.
- Extended non-compliance beyond 24 months: 5% of the cost of the relevant foreign property or indebtedness.
There is a de minimis threshold. Transactions with a particular non-resident totaling less than $100,000 in a tax year do not require detailed reporting in Part III of the T106 slip, but the return itself must still be filed.9Canada Revenue Agency. Form T106 Information Return of Non-Arm’s Length Transactions with Non-Residents – De Minimis Policy
What to Track Through the Year
Working out thin capitalization accurately means capturing several figures on an ongoing basis: monthly debt outstanding to each specified non-resident (to identify the peak), monthly balances of paid-up capital and contributed surplus attributable to specified non-resident shareholders, and retained earnings at the first day of the tax year.
These figures feed the T2 Corporation Income Tax Return, which is due six months after the end of the fiscal year. Alongside the T2, corporations transacting with non-arm’s length non-residents file the T106, which identifies each non-resident party, their country of residence, and the nature of the transactions. Internal working papers that bridge audited financial statements to the return figures are what a CRA auditor will ask for first, and the T106 penalty structure gives that request real weight.