Cash Damming: The Mortgage Strategy Self-Employed Canadians Keep Missing

In Canada, the interest on your home mortgage is normally a personal expense: you pay it with after-tax dollars and it deducts nothing. Interest on money borrowed to earn business or rental income is different: it is generally deductible. Cash damming lives in the gap between those two sentences.

It is not a loophole and it is not exotic. It is an established structure with real court history behind it, used by self-employed Canadians and rental property owners who simply route their cash flows deliberately instead of by habit. It does demand discipline and clean records, which is why most people have never had it explained properly.

The idea in one paragraph

Your business or rental property produces income and it also has expenses. Normally you pay those expenses out of the income and use whatever is left however you like. With cash damming, you flip the routing: the income goes toward your home mortgage, aggressively paying down your non-deductible debt, while the expenses get paid from a dedicated line of credit. That borrowed money was used to fund the business or property, so its interest is generally deductible. Over time, non-deductible mortgage shrinks fast while a deductible balance grows in its place. Same total debt, better tax character.

What you need for it to work

• Qualifying income. Sole proprietor income or rental income are the classic fits. Salaried employment income does not qualify: this is a strategy about business borrowing, and employees do not have business expenses to fund.
• The right mortgage structure. The clean setup is a readvanceable mortgage: a mortgage paired with a line of credit whose room grows as the mortgage shrinks. Every prepayment opens matching borrowing room, so the conversion runs continuously.
• Separation and records. One line of credit used only for the business or property expenses, never for groceries or a vacation. Mixing personal spending into the borrowing is the classic way people break the deductibility, so the accounts stay separate, full stop.
• An accountant in the loop. The mortgage structure is our job. Confirming the deductions and filing them correctly is your accountant's. Every cash damming setup we build assumes both professionals are involved.

Who it fits, and who it does not

It fits a self-employed contractor with steady revenues and real expenses, a landlord with one or more rentals, or a professional running an unincorporated practice, in each case with a meaningful mortgage on their own home. The bigger the expenses flowing through the structure, the faster the conversion works.

It does not fit purely salaried households, and it does not suit anyone who will not keep the accounts separated. The strategy is only as strong as its paper trail. If your bookkeeping is chaos, fix that first: the structure will still be here.

Seeing your own numbers

We built a free cash damming calculator and workbook at mudrickmortgages.com/cash. Put in your mortgage, your business or rental cash flows, and it shows the conversion year by year: how fast the non-deductible balance falls and what the structure is worth to you. If the numbers look interesting, we set up the mortgage side and connect the plan with your accountant.

This article is general information, not tax advice. Whether cash damming works in your situation depends on your income sources and how the flows are documented. Confirm your setup with your accountant or tax professional before acting.