Cash Damming in Ontario
If you run an unincorporated business or own a rental property, some of your interest is already tax-deductible and some of it is not. Cash damming is a strategy that gradually moves your debt from the non-deductible side to the deductible side, without increasing what you owe. It is a tax strategy your accountant confirms, built on a mortgage structure we set up.
The Idea in One Paragraph
In Canada, interest is deductible based on what the borrowed money was used for. Borrow to earn business or property income and the interest is generally deductible. Borrow to buy your home and it is not. Cash damming flips the order of your cash flow: your business or rental revenue goes toward the personal mortgage, while a line of credit covers the business or rental expenses. The total debt stays the same. Its tax character changes.
Before
Revenue pays your business or rental expenses. Whatever is left goes toward the mortgage. The mortgage interest is not deductible.
After
Revenue goes at the mortgage. A line of credit pays the operating expenses. That borrowing is tied to earning income, so its interest is generally deductible.
The Result
Same total debt, but a shrinking non-deductible mortgage and a growing deductible loan. The deduction produces an annual tax saving you can put back against the mortgage.
Who It Suits
Cash damming is narrow by design. It needs two things: a personal mortgage that is not deductible, and a source of business or rental expenses to redirect.
Unincorporated Business Owners
Sole proprietors and partners in a general partnership with real operating expenses, from contractors and consultants to professionals running their own practice. Partnerships carry extra restrictions, so that case needs a tax specialist before anything moves.
Rental Property Owners
Landlords with property taxes, management fees, maintenance and repairs. Rental income goes at your own mortgage while borrowing covers the rental costs.
You Still Carry Personal Debt
The strategy converts non-deductible personal debt, usually a mortgage, though a car loan can qualify too. If you owe nothing personally, there is nothing to convert.
You Have Steady Surplus Cash Flow
A line of credit still has to be serviced. The strategy suits businesses with reliable revenue, not ones already stretched.
You Qualify for the Credit Line
None of this works without the borrowing facility, and that means credit. A strong score and clean history are what get the line approved at a workable rate, so it is worth checking before you plan around the strategy.
The Part That Is Ours
Your accountant confirms the tax treatment. What makes the strategy possible in the first place is the borrowing structure, and that is mortgage work.
The Right Facility
Cash damming needs a line of credit you can draw on cleanly, often a readvanceable mortgage with separate sub-accounts. Not every lender offers one, and not every product supports the separation the strategy relies on.
Separation That Survives Review
Deductibility depends on tracing borrowed money to an income-earning use. A structure with distinct accounts from day one is far easier to defend than one untangled years later.
Rate and Penalty Math
Line of credit rates usually sit above mortgage rates, and breaking a mortgage early can trigger a penalty. We calculate whether the tax saving actually clears those costs before you commit.
The Honest Tradeoffs
This strategy is genuinely useful for the right file and a poor fit for plenty of others. Here is the other side.
A Higher Rate Can Cancel the Benefit
If the line of credit rate is far enough above your mortgage rate, the extra borrowing cost eats the tax saving. There is a break-even, and it is worth calculating before anything moves.
The Record-Keeping Is Real
Deductibility rests on being able to link borrowed money to an income-earning purpose. That means disciplined accounts and clean records, every year.
Debt Without a Deadline
You are trading a mortgage with an end date for a credit line that has none. Without the discipline to repay it, the debt simply persists.
Prepayment Penalties
Paying a mortgage down faster than your privileges allow can trigger a charge. Check the terms before redirecting cash flow at it.
It Works in Years, Not Months
Your net personal debt does not change overnight. Lenders generally think about this in three to five year cycles, and it only pays off if you stay disciplined and keep the flows separate that whole time.
Separation Complicates It
Because the strategy deliberately changes which debts sit where, a separation during or after the conversion can create real inequities in how assets and debts get divided. Couples should go in with that understood, and with legal advice if the relationship is in question.
How We Work It Through
A short, honest process. If the numbers do not clear, we tell you.
We Check the Fit
Do you have non-deductible mortgage debt and redirectable business or rental expenses? If either is missing, the strategy does not apply and we say so.
We Run the Break-Even
We model the annual tax saving against the higher line of credit cost and any penalty, so you can see the net rather than the headline.
Your Accountant Confirms
The tax treatment is theirs to approve. We share the structure and the numbers so the conversation is concrete.
We Structure the Financing
We source the readvanceable mortgage or line of credit that supports clean separation, and set it up properly from the start.
Find Out Whether It Fits
Tell us about your business or rental and your current mortgage. We will run the break-even and give you a straight answer, including when the answer is no. No cost, no obligation.