A Lower Tax Rate Can Quietly Weaken Your Borrow-to-Invest Mortgage
The investment loan was set up in a year when every dollar of interest came back at 53.5 cents. That's British Columbia's top combined federal and provincial marginal rate in 2026, and for a business owner earning well into that bracket, it made borrowing to invest look cheap.
The pattern is common enough in Abbotsford that it's worth walking through. An owner with a healthy company and a large mortgage restructures into a readvanceable mortgage. As the home balance gets paid down, the freed-up room is borrowed back to buy a non-registered portfolio. Under CRA rules, interest on money borrowed to earn income is deductible, while interest on a home mortgage is not. It's the Smith Manoeuvre™ in its basic form, and it was a sound decision. The trouble arrives later, when the owner's personal tax rate falls and the loan keeps running as if nothing happened. Any deduction is worth exactly your marginal rate, so when that rate drops, the strategy gets more expensive in silence, and nobody sends you a bill for it.
The deduction is only worth your rate
Here is illustrative arithmetic, with round numbers chosen for clarity. Say the investment loan is $400,000 at 5% interest. That's $20,000 a year in deductible interest.
At a 53.5% marginal rate, the deduction saves $10,700. The after-tax cost of the loan is $9,300, or about 2.3% on the balance. The portfolio only needs to beat that after its own taxes to come out ahead.
Now drop the owner's personal income to around $90,000, where the combined BC marginal rate is 31.0%. The same $20,000 of interest saves $6,200. The after-tax cost rises to $13,800, about 3.45%. Same loan, same rate, same portfolio, and the hurdle went up by $4,500 a year.
Your rate moves for reasons unrelated to the loan
In this typical case, the drop came from good advice. The accountant suggested leaving more profit inside the corporation, where it's taxed at a lower rate, and drawing a modest salary. On its own, that was the right call. It simply never got connected to the mortgage file.
Plenty of other things move a marginal rate. A slow year for the business. A shift from salary to dividends. Selling the company, or easing toward retirement. Brackets get indexed to inflation every year, and governments do adjust rates. The federal top rate in Canada sits at 33% for 2026, and any change to it, or to BC's portion, flows straight into what your deductions are worth.
Rising rates add a wrinkle. If your borrowing rate climbs while your tax rate falls, the dollar amount you deduct can still go up, which feels like more savings. Measure the after-tax cost as a percentage of the balance instead, and the picture gets clearer.
Treat any change to your tax rate as a review date for the debt
The leveraged structure may still be the right one. If the portfolio is expected to earn meaningfully more than 3.45% after tax over the long run, the math can still work. It just works with a thinner cushion, and a bad couple of years in the market hurts more than it did when the CRA was absorbing over half the interest.
The alternatives deserve a fresh look at the same time. Paying down a 5% non-deductible mortgage is a guaranteed 5% after-tax return, with no market risk attached. Extra take-home pay from a lower personal tax bill could go to TFSA or RRSP room, which doesn't depend on deductibility at all. For some owners, the better question becomes whether the debt belongs on the personal side or the corporate side.
None of this requires guessing what Ottawa or Victoria will do next. It requires one habit: whenever your income, your pay structure or the tax rules change, pull out the loan and recalculate its after-tax cost at the rate you actually pay now. Whatever number comes back is the hurdle your portfolio has to clear.
The investment loan was set up in a year when every dollar of interest came back at 53.5 cents. That's British Columbia's top combined federal and provincial marginal rate in 2026, and for a business owner earning well into that bracket, it made borrowing to invest look cheap.
The pattern is common enough in Abbotsford that it's worth walking through. An owner with a healthy company and a large mortgage restructures into a readvanceable mortgage. As the home balance gets paid down, the freed-up room is borrowed back to buy a non-registered portfolio. Under CRA rules, interest on money borrowed to earn income is deductible, while interest on a home mortgage is not. It's the Smith Manoeuvre™ in its basic form, and it was a sound decision. The trouble arrives later, when the owner's personal tax rate falls and the loan keeps running as if nothing happened. Any deduction is worth exactly your marginal rate, so when that rate drops, the strategy gets more expensive in silence, and nobody sends you a bill for it.
The deduction is only worth your rate
Here is illustrative arithmetic, with round numbers chosen for clarity. Say the investment loan is $400,000 at 5% interest. That's $20,000 a year in deductible interest.
At a 53.5% marginal rate, the deduction saves $10,700. The after-tax cost of the loan is $9,300, or about 2.3% on the balance. The portfolio only needs to beat that after its own taxes to come out ahead.
Now drop the owner's personal income to around $90,000, where the combined BC marginal rate is 31.0%. The same $20,000 of interest saves $6,200. The after-tax cost rises to $13,800, about 3.45%. Same loan, same rate, same portfolio, and the hurdle went up by $4,500 a year.
Your rate moves for reasons unrelated to the loan
In this typical case, the drop came from good advice. The accountant suggested leaving more profit inside the corporation, where it's taxed at a lower rate, and drawing a modest salary. On its own, that was the right call. It simply never got connected to the mortgage file.
Plenty of other things move a marginal rate. A slow year for the business. A shift from salary to dividends. Selling the company, or easing toward retirement. Brackets get indexed to inflation every year, and governments do adjust rates. The federal top rate in Canada sits at 33% for 2026, and any change to it, or to BC's portion, flows straight into what your deductions are worth.
Rising rates add a wrinkle. If your borrowing rate climbs while your tax rate falls, the dollar amount you deduct can still go up, which feels like more savings. Measure the after-tax cost as a percentage of the balance instead, and the picture gets clearer.
Treat any change to your tax rate as a review date for the debt
The leveraged structure may still be the right one. If the portfolio is expected to earn meaningfully more than 3.45% after tax over the long run, the math can still work. It just works with a thinner cushion, and a bad couple of years in the market hurts more than it did when the CRA was absorbing over half the interest.
The alternatives deserve a fresh look at the same time. Paying down a 5% non-deductible mortgage is a guaranteed 5% after-tax return, with no market risk attached. Extra take-home pay from a lower personal tax bill could go to TFSA or RRSP room, which doesn't depend on deductibility at all. For some owners, the better question becomes whether the debt belongs on the personal side or the corporate side.
None of this requires guessing what Ottawa or Victoria will do next. It requires one habit: whenever your income, your pay structure or the tax rules change, pull out the loan and recalculate its after-tax cost at the rate you actually pay now. Whatever number comes back is the hurdle your portfolio has to clear.
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