Co-Signing or Guaranteeing a Mortgage in Canada

Co-signing a mortgage means signing the loan alongside the buyer, and usually going on the title as an owner too. Guaranteeing it means backing the loan without owning any of the property. Either way, you are fully liable for the debt if the borrower stops paying: if they miss payments, your credit suffers, and if they default, the lender can come after you for the full amount. Getting off the mortgage later usually means the borrower has to requalify alone. This page explains both roles, what they cost the person providing the support, and the other ways to help someone buy. It is part of our guides to mortgages outside the standard bank route.

Co-signer vs co-borrower vs guarantor

In practice, lenders in Canada use “co-signer” and “co-borrower” almost interchangeably: both go on the mortgage with full liability, and usually on title. The meaningful legal line is between those roles and a guarantor, who backs the debt but has no ownership stake.

When lenders ask for a co-signer or guarantor

If the borrower’s main problem is a low score, our guide to getting a mortgage with bad credit covers the other routes. For an insured mortgage, CMHC’s credit test can be met by a guarantor: For a CMHC-insured purchase, at least one borrower or guarantor needs a credit score of 600 or more; CMHC may use other ways to judge creditworthiness for a borrower with no credit history.

Co-signer or guarantor: which role fits

Going on title as a co-signer makes sense when the supporting person wants or needs ownership:

• they are paying part of the down payment and want a legal share for it;
• they plan to live in the home, as when a parent and an adult child buy together;
• their estate plan relies on owning part of the property;
• the arrangement is a partnership rather than a backstop.

When the borrower will live in the home alone and the supporter wants no stake in it, a guarantee gives the lending support without the ownership, capital gains and land transfer tax complications. When the plan is to buy and own together, the arrangement is really co-ownership: buying a home with friends or family covers title, the written agreement and exits, and couples are covered in joint mortgages for spouses and partners.

The risks for the person signing

If the borrower defaults

How a guarantee affects your own borrowing

Lenders count a mortgage you co-sign or guarantee as your debt, even when the borrower makes every payment. For an insured mortgage, CMHC caps your housing costs at 39% of gross income (GDS) and your housing costs plus other debt payments at 44% (TDS); lenders set their own limits for uninsured mortgages. The example below uses the 44% TDS limit as the yardstick.

In this example the whole guaranteed payment comes out of the room this person had for their own housing costs. Some lenders will leave a guaranteed payment out of the ratios once the borrower has a record of paying it from their own account, but that is lender-specific and can’t be assumed.

What shows on your credit report

Protecting yourself before you sign

1. Independent legal advice. Your own lawyer, separate from the borrower’s, can explain exactly what the documents commit you to.
2. A test of whether you could carry the payments. The arrangement is only as safe as your ability to make the payments yourself if the borrower stopped.
3. An exit agreed in writing. Set when and how you come off the mortgage, for example at the first renewal or once the borrower’s income reaches an agreed level, and document it even between family members.
4. A limited guarantee. Some lenders accept a guarantee capped at part of the mortgage rather than the whole balance.
5. Payment monitoring. Notifications or account access let you see a missed payment when it happens.
6. Life insurance on the borrower. A policy that pays off the mortgage if the borrower dies releases you from the debt.

Getting removed from the mortgage

At renewal

Renewal is the cheapest time to come off a mortgage:

1. The borrower applies to renew, with the same lender or a new one, in their name only.
2. They must qualify for the whole mortgage alone, including the mortgage stress test and the lender’s debt ratios.
3. If approved, the new mortgage is registered without you.
4. A co-signer on title also needs a title transfer, which can trigger land transfer tax in some provinces.

During the term

Coming off mid-term means the borrower refinances in their name only, which ends the existing mortgage early. Breaking a closed mortgage, paying it off early or prepaying more than your privileges allow usually costs the higher of 3 months' interest and the interest rate differential (IRD) on a fixed rate, and typically 3 months' interest on a variable rate; your mortgage contract sets the exact method and comparison rate, and a federally regulated lender must tell you how it calculates the penalty. Legal fees for the new registration and an appraisal are usually added, plus title transfer costs if a co-signer is leaving the title.

Waiting for renewal avoids the penalty entirely. Adding someone to a mortgage you already hold, or taking a person off it, raises its own lender, title and tax questions, covered in adding someone to your mortgage.

Alternatives to co-signing or guaranteeing

The bottom line

Co-signing and guaranteeing both put the full mortgage on your credit and your debt ratios while someone else lives in the home. A co-signer gets an ownership share for that risk; a guarantor gets none. The arrangement works best when the borrower needs temporary support and has a realistic path to qualifying alone, with the exit agreed in writing before anyone signs.