What Is Cash Damming? The Landlord's Guide to Tax-Deductible Rental Expenses

Cash damming — also called the cash dam or cash flow dam strategy — is one of the most quietly effective moves available to Canadian landlords, and one of the least talked about. It doesn't require new debt or a new property. It just requires paying your existing bills in a different order.

The One-Sentence Version

Cash damming uses a line of credit to pay your tax-deductible rental property expenses, while your rental income is freed up to pay personal, non-deductible expenses instead — making the interest on that line of credit tax-deductible.

How the Cash Dam Actually Works

1. You have a rental property and a line of credit (often a HELOC on your principal residence or the rental itself).
2. Instead of paying rental expenses — property tax, insurance, repairs, mortgage interest on the rental — out of your regular bank account, you pay them from the line of credit.
3. Your rental income, which would normally cover those expenses, is now free to pay personal living expenses instead.
4. Because the line of credit was used to earn rental income, the interest on it becomes tax-deductible under the same traceability rule that underlies the Smith Manoeuvre.

Why Landlords Use It

Without cash damming, a landlord typically pays down their line of credit or personal debt with whatever's left over from rental income — and that debt is non-deductible personal debt. With cash damming, the same cash flow ends up covering personal expenses, while the debt that grows is the deductible kind. Nothing about your total spending changes. What changes is which debt is doing the growing.

What Qualifies

Only genuine rental property expenses paid through the line of credit qualify — mortgage interest, property tax, insurance, repairs and maintenance, property management fees. The moment personal spending gets mixed into that line of credit, the deduction on the whole balance is at risk.

Where Landlords Get This Wrong

The single biggest mistake is using one account for both rental expenses and personal spending. CRA's traceability rule requires a clean, documented paper trail showing exactly what the borrowed money was used for. Keep a dedicated line of credit for rental expenses only, and the deduction holds up. Blend it with day-to-day spending, and you're gambling with it.

Curious what cash damming would add up to on your own rental property? Try the Mortgage-To-Millions™ Calculator to see the numbers.