BoC Flags Parental Co-Signing of Mortgages Tripling to 11% as Emerging Systemic Vulnerability

Using linked TransUnion and OSFI administrative mortgage data, Bank of Canada researchers found that parental co-signing on first-time-buyer mortgages — among buyers under 50 — rose from about 4% in 2004 to roughly 11% by 2025. In Toronto and Vancouver, the rate is closer to 14%. The practice is concentrated among younger buyers with lower credit scores and lower incomes, which is consistent with co-signing being an underwriting solution rather than a discretionary preference.

The headline number is the trend. The more useful number is the dependency. Seventy-four per cent of co-signed buyers would not have qualified for their current mortgage on their own. Co-signing, in other words, is not topping up a marginal application. It is the difference between getting the loan and not.

A separate Bank of Canada working paper on housing affordability extends the same series back further, showing co-signed buyers enter the market about five years younger than their non-co-signed peers and at credit scores roughly 4% lower. The pattern is structural, not anecdotal. Roughly one-third of co-signing parents already have a mortgage of their own, sometimes with an attached home equity line of credit — meaning a meaningful share of co-signers are layering contingent mortgage exposure on top of existing housing debt.

The mechanics here are economic, not emotional. Canadian mortgage underwriting runs through two debt-service ratios — gross debt service (GDS) and total debt service (TDS) — plus a payment-to-income (PTI) check that became binding after the 2018 stress-test reforms. When a parent co-signs, the lender effectively folds the parent's income into the qualification math, relaxing the constraint that would otherwise cap the child's borrowing.

The Bank of Canada quantified what this loosening produces. In late 2022, co-signed buyers could have afforded an average home of $458,000 on their own. With a parent on the file, their maximum purchasing power jumped to roughly $787,000 — a 72% increase. They actually bought homes averaging $709,000, capturing about three-quarters of the extra room the co-signer created.

That utilisation rate matters. The central bank found that borrowers who used the most additional purchasing power went on to experience the largest subsequent increases in delinquency on credit cards and lines of credit. The same balance-sheet expansion that got the buyer into a more expensive home appears to be feeding back into stress elsewhere in the household.

This is the part most coverage skips. The central bank is interested in financial-system risk, and most retail commentary treats co-signing as a one-time generosity question. The homeowner-side reality is a multi-year set of constraints that follow the parent until the loan is gone or the child has refinanced alone.

The starting point is the federal definition. The Financial Consumer Agency of Canada classifies a co-signer as a joint borrower who is "equally responsible for repaying the unpaid balance." There is no softer version of that obligation. The contract treats the parent and the child as a single underwriting unit until the mortgage is discharged or the parent is formally removed from title and the loan.

From there, four mechanics matter for the parent's own balance sheet.

Your borrowing capacity drops dollar-for-dollar. Lenders include the full co-signed mortgage in the parent's GDS and TDS calculations whether they live in the property or not. That counts against future credit applications — another mortgage, a refinance, a home equity line of credit, or any consumer borrowing the parent might want in retirement.

Your credit profile is exposed to a payment you don't control. Late or missed payments by the primary borrower flow to the co-signer's credit report the same way they would for the parent's own debts. A pattern of delinquency on the child's mortgage can scar the parent's credit history even when every other obligation is paid on time.

At renewal, the lender re-tests both balance sheets. Renewal is not automatic when stress-test or qualification rules have shifted, especially if the household is moving lenders or refinancing. A drop in the parent's income — common at retirement — can knock the combined application off side at exactly the moment the household needs continuity.

Exiting requires the child to re-qualify alone. Removing a co-signer is not a clerical change. The lender treats it as a fresh underwriting decision, usually at current rates and under current rules. If the child could not qualify alone at 5%, the answer at 6% is not better.

The timing of this research matters. The OSFI 2026–27 Annual Risk Outlook flagged about 3.1 million Canadian mortgages — roughly 52% of the outstanding book — coming up for renewal by the end of 2027. Of those, 1.3 million are fixed-rate or variable-with-fixed-payment loans originated during the 2021–2022 low-rate window. The regulator is openly expecting "material" payment increases for that cohort and has noted that delinquencies are already rising.

Co-signed mortgages sit inside that wave. They share the same renewal arithmetic, but with two household income statements feeding the underwriting decision instead of one. That doubles both the upside and the failure modes: a job loss, a retirement, an income-replacement event for either household can put the renewal at risk. The Bank of Canada's concern about spreading mortgage risk across two household balance sheets is not abstract — it is what happens when a 2021-vintage mortgage at 1.99% comes up for renewal at 5%, and both the primary borrower and the co-signer have to clear the new payment together.

Survey data is moving in the same direction as the regulatory signal. A recent TD Bank survey found two-thirds of Canadian homeowners anxious about their upcoming renewal, with a majority planning to cut spending to absorb the increase. Co-signed households face that same arithmetic on a joint balance sheet.

The Bank of Canada chose its language carefully. Calling parental co-signing "an emerging vulnerability for the financial system" places it in the same category as other macroprudential concerns the central bank monitors — household debt levels, mortgage concentration on bank balance sheets, regional housing-market stress. The mechanism is straightforward. Mortgages are the largest single liability on Canadian household balance sheets and the largest asset class on Canadian bank balance sheets. Anything that links those balance sheets in correlated ways makes the system more sensitive to a common shock.

The working paper also identifies a regulatory feedback loop. Canada's 2016 and 2018 mortgage stress-test reforms tightened payment-to-income limits, and the research finds that parental co-signing increased in response — particularly for borrowers close to the qualification threshold. Tighter underwriting did not eliminate the risk. It redistributed it onto parental balance sheets.

That dynamic is showing up elsewhere. The CMHC 2026 Mortgage Consumer Survey reported that 28% of first-time buyers needed a co-signer, aside from a partner or spouse, to purchase their home, and more than half of those co-signers were parents. The figures triangulate with the central bank's administrative data — different methods, same pattern.

OSFI's current supervisory posture rounds out the picture. The regulator has imposed institution-specific portfolio limits on uninsured mortgages with loan-to-income ratios above 4.5×, with particular focus on stress in variable-rate fixed-payment mortgages and smaller lenders concentrated in Toronto and Vancouver — the same markets where parental co-signing is most prevalent. Co-signed borrowers, by definition, are leveraging combined income to clear loan-to-income thresholds, which puts them squarely inside the population the regulator is trying to bound. Independent analysis covered in Morningstar DBRS's review of OSFI's dual safeguard frames why the regulator is reluctant to relax either constraint while the renewal wave is still in motion.

The broader macro picture matters too. Canadian household credit balances continue to grow, with mortgages now claiming a record share of total household debt — context laid out in Homeowner.ca's coverage of the $3.24 trillion household debt milestone. Co-signed mortgages are a small but rising slice of that aggregate, and their distinguishing feature is that they correlate two household balance sheets to a single loan.

The Bank of Canada is not telling families what to do. It is telling regulators, lenders, and policy makers what to watch. For homeowners considering — or already on — a co-signed mortgage, the right read is that a household-level decision is being upgraded to a system-level concern, and the practical implications for parents' borrowing capacity, credit, and retirement balance sheet are not theoretical. A thirty-minute conversation with a qualified mortgage broker or financial advisor is inexpensive. A co-signed mortgage that constrains your own borrowing for the next two decades is not.