Cash Damming in Canada: Steps, Tracing, and the Smith Manoeuvre Difference
- Paragraph 20(1)(c) and Income Tax Folio S3-F6-C1 are the test: interest on money borrowed for the purpose of earning income from a business or property can be deductible. Interest on money borrowed to buy the home you live in is not.
- Cash damming borrows to pay current expenses of the rental or the business, and uses the gross receipts to pay down personal debt. The Smith Manoeuvre borrows to buy investments and readvances as you pay the residence mortgage. They are different uses of a line. Mixing them in one tranche is how the tracing fails.
- CRA has not issued a product approval called "cash damming." The folio is a direct-use and purpose test. A clean sub-account is the evidence. A commingled chequing account is a reconstruction project.
- The interest rate on the line can be higher than the mortgage you are paying down. Part of the "saving" is a rate swap. Price it before you feel clever.
- If you sell the rental or stop the business, the purpose ends. So does the deduction, unless you reborrow into another current income-earning use and can still trace it.
The single-row version of this idea lives inside HELOC strategies. The investment loop is the Smith Manoeuvre. Whether the credit limit grows when you pay principal is the readvanceable mortgage. Cash damming can run on a plain secured line. It does not need the limit to regenerate, until the line is full. A readvanceable product is what keeps room appearing after that.
What are you actually rotating?
| Cash damming | Smith Manoeuvre | |
|---|---|---|
| What the borrowed dollar pays | Current expenses of a rental or a business you already operate: interest, tax, insurance, repairs, or business inputs | A non-registered portfolio with a reasonable expectation of income |
| Where the income goes | Against the residence mortgage, or other non-deductible debt | The portfolio stays invested. The residence mortgage is paid on its normal schedule, and principal paid frees credit |
| What becomes deductible | Interest on the line, to the extent the borrowed money traces to those income-earning expenses | Interest on the investment loan, if the use test holds all year |
| What stays non-deductible | Interest on the residence mortgage | Interest on the residence mortgage |
| What has to be true first | You have rental or business expenses you would have paid anyway, and gross receipts you can redirect | You can qualify for the credit, tolerate the leverage, and keep a dedicated investment account |
A sole proprietor's version is the same rotation with a different deposit. Business revenue that would have paid rent, supplies, or a subcontractor's invoice is sent to the residence mortgage instead, and the line pays those business costs. The folio does not care that the income is on a T2125 rather than a T776. It cares that the borrowed dollar paid an expense incurred to earn income, and that you can show the path. A corporation is a worse casual fit. The company is a separate taxpayer. Having the company pay the owner's mortgage, or having the owner borrow personally against a corporate expense, is a shareholder-benefit problem wearing a cash-dam label. Keep the pattern inside one taxpayer unless a tax advisor has drawn the intercompany piece. The personal rental is the case this article's numbers use.
A rental's own mortgage interest, property tax, insurance, and repairs are already deductible against rental income on the T776 when they were incurred to earn rent. Cash damming does not invent that deduction. It changes which debt sits under expenses you were paying from the rent. Over time, non-deductible principal falls and deductible principal rises. Net worth rises only if the tax saving and the principal you retired beat the extra interest and the risk of a second loan. The deduction list for the property itself is rental property tax deductions. A sole proprietor running the same pattern against business expenses is in the same folio, with a different statement. The filing side of self-employment is the self-employed tax guide.
The steps
- Separate the debts before the first transfer. Ask the lender for a segment or a sub-account with its own statement. The residence mortgage stays the residence mortgage. The line pays rental or business expenses and nothing else. Groceries, a TFSA contribution, and a kitchen renovation do not touch it.
- List the expenses that qualify before you borrow them. They are the expenses you could have deducted if you had paid them from the rent. A personal bill you route through the rental "because the line is open" fails the purpose test and contaminates the trace.
- Deposit the rent or the revenue to an account that pays the residence mortgage. Do not run it through the line. The whole point is that the income dollar retires non-deductible principal, and the borrowed dollar pays the deductible expense.
- Pay each expense from the line, with a memo you could show an auditor. Transfer records, invoices, and the annual interest statement are the file. A one-page note written the week you start, stating the purpose, beats a memory.
- Claim interest only on the clean balance. If any personal dollar entered the tranche, you do not estimate a percentage from a feeling. You reconstruct, or you stop claiming until the balance is clean again. Folio S3-F6-C1 is the document your accountant will actually open.
- When the rental is sold or the business stops, stop. Repay the line or move the borrowed money into another current use that still earns income, and document the move. A line that once paid a furnace and now pays a car is a personal loan with a rental story attached.
I ran the numbers on a five-year rotation
The dollars are a teaching picture, the same shape as the illustration already on the HELOC page, extended so the interest is visible. They are not your rent and not a rate quote. Gross rent is $3,000 a month, $36,000 a year, and all of it is sent to the residence mortgage. Expenses you would have paid from that rent, other than the residence mortgage, are $1,400 a month, $16,800 a year, and those are drawn from the line on January 1 of each year so the arithmetic is easy to audit. The line is interest-only at an assumed 6 percent. The residence mortgage rate is an assumed 4 percent. Neither rate is a lender's offer. The prepayment calculator is where a real contract rate and a real amortization belong. This table ignores the contractual payment schedule. It only asks what the extra principal and the new interest look like if you hold the assumptions still.
| Year | Line balance after the draw | Interest on the line at 6 percent | Extra principal sent to the residence mortgage that year |
|---|---|---|---|
| 1 | $16,800 | $1,008 | $36,000 |
| 2 | $33,600 | $2,016 | $36,000 |
| 3 | $50,400 | $3,024 | $36,000 |
| 4 | $67,200 | $4,032 | $36,000 |
| 5 | $84,000 | $5,040 | $36,000 |
Interest paid on the line over five years is $15,120. If every dollar of that interest is deductible and the marginal rate is an assumed 43 percent, the tax reduction is about $6,502 and the after-tax cost of the line interest is about $8,618. You still paid the interest. The other side of the trade is principal gone from the residence mortgage: $180,000 over five years. At an assumed 4 percent, a balance that is lower by the full cumulative prepayment would avoid about $7,200 of residence interest in year 5 alone. That sentence is a ceiling on the illustration, not an amortization. Early in the five years the balance is only lower by one year's prepayment, so the interest avoided is smaller, and a real mortgage payment also rewrites principal and interest every month. Price your own contract. Do not borrow because $7,200 appeared in a table.
Take the $16,800 of new line in year 1 and buy dividend-paying investments in a non-registered account instead of paying the rental's insurance and repairs. That is no longer cash damming. The rental expenses are still paid from the rent, the residence mortgage does not receive the $36,000, and you now have market risk on top of the interest. Both structures can be deductible. They are deductible for different uses. Running both through one HELOC statement, with a TFSA contribution in the middle, is how a supportable file becomes a percentage you cannot defend. Pick one use per tranche.
The tracing mistakes that undo the year
- One card for everything. The line that pays the rental's property tax and also the family's groceries is a mixed-use debt. The folio does not let you claim "most of it."
- Borrowing to contribute to an RRSP, TFSA, or FHSA. The income inside those accounts is not taxed in your hands. The purpose test fails even when the contribution is a good idea on its own.
- Paying the rental expense from the rent, then borrowing the same amount to spend. That is a personal draw with extra steps. The borrowed money has to be the money that pays the expense.
- A joint line and one spouse's rental. The person who claims the interest should be the person who owes it and who owns the income. Attribution and beneficial ownership are not cured by a nickname. Get advice before the first transfer if both names are on the credit.
- Capital cost versus current expense. A repair can be current. A renovation that improves the property can be capital. Capital cost allowance is a different claim from interest. Do not run a new roof through the "expense" column because the line paid the contractor.
Frequently asked questions
Does CRA allow cash damming?
CRA does not approve strategies by marketing name. Folio S3-F6-C1 and paragraph 20(1)(c) allow interest to be deducted when the borrowed money is used to earn income from a business or property, subject to the limits in the Act. A cash-dam file that meets that use test is a deduction. A file that does not is a personal line with a story. There is no advance ruling hiding in the nickname.
Do I need a readvanceable mortgage?
Not on day one. You need a line that can fund the expenses, kept separate from personal spending. You need a readvanceable limit when the ordinary line is full and you still want new room as you pay the residence mortgage down. The product terms, including any 65 percent revolving cap your lender applies, are in the commitment. They are not in this article.
Is this better than just paying the rental expenses from the rent?
Only if the after-tax cost of the new interest is smaller than the residence interest you avoid, and you can carry the extra debt through a vacancy. A vacant month still accrues line interest. The rent you redirected is gone. Run the vacant case before you automate the transfers.
Can I cash-dam a room I rent in my own house?
Only the expenses that are actually incurred to earn that income, allocated on a basis you can explain. You cannot move the entire residence mortgage into the deductible column because a bedroom has a tenant. Mixed-use houses are an allocation problem. They are not a loophole.
What happens to the line when I sell the rental?
The purpose of that borrowing ended unless you reinvest the borrowed money in another income-earning use and can trace it. Repaying the line from the sale proceeds is the clean version. Leaving it outstanding and spending the proceeds is how deductible interest becomes personal interest in the year of the sale.
Should the tax refund go against the mortgage?
If you want the rotation to accelerate, yes. A refund you spend does not undo the deduction you already claimed. It just fails to create the next dollar of principal reduction. Write the choice down so a spring deposit does not become a vacation by accident.
