Rental Offset

Rental Offset is the practice of a lender counting a portion of the rental income from a property — a secondary suite, a duplex unit, or a basement apartment — toward a borrower's income when qualifying for a mortgage. It affects how much housing cost a borrower can reasonably carry and therefore how large a mortgage a lender may be willing to approve.

How lenders treat rental income

Rental offset works through the two debt service ratios lenders use to test affordability: the Gross Debt Service (GDS) ratio, which compares housing costs to gross income, and the Total Debt Service (TDS) ratio, which adds all other debt payments. Rental income that a lender accepts is added to gross income, which raises both denominators and can increase the mortgage a borrower can carry.

Lenders rarely count every dollar of rent. They typically apply a vacancy allowance or an offset ratio for the subject property and account for operating costs, so the amount added to qualifying income is usually less than the rent actually collected. Treatment varies by lender, by property type, and by mortgage program, and defaults to conservative assumptions where income cannot be documented. For insured loans, CMHC sets its own underwriting expectations, so confirm the current rules with the lender or on the CMHC website.

Which properties qualify

Rental offset is most common on owner-occupied properties where the borrower lives in one unit and rents another — a house with a legal secondary suite, a duplex, or a small multi-unit property within the lender's permitted limits. It can also apply to a property with a garden suite or a separately metered unit. Purely investment properties are usually underwritten on a different basis and may be assessed using debt service coverage rather than personal income.

Legal status matters. An unregistered suite, zoning restrictions, or an unpermitted unit can prevent the income from being counted at all, so buyers should verify the suite's status before assuming the rent will help them qualify.

Why it matters to a borrower

A rental offset can change the maximum purchase price a buyer can afford. Consider two buyers with identical jobs and debts looking at similar homes:

• Without offset, the lender ignores suite income and qualifies the buyer on employment income alone.
• With offset, a share of the documented rent is added to qualifying income, which can support a larger mortgage on the same ratios.

The borrower must still pass the federal mortgage stress test, which qualifies them at a higher rate than the contract rate. Lenders generally want a signed lease, a market rent estimate, or a rental income worksheet as evidence. See GDS and TDS ratios for how the two measures interact.