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A co-borrower is a person who applies for a mortgage jointly with another borrower, sharing both ownership of the property and full responsibility for repayment from the outset of the application, most often a spouse, partner, or family member buying together.
In everyday use the terms overlap, but “co-borrower” typically describes a joint applicant who intends to live in and own the property together, applying from day one — rather than someone added later specifically to help another applicant qualify. That second role is usually described as a co-signer.
Like a co-signer, a co-borrower’s income and debts are fully counted in qualifying income and the debt-service ratios, and each co-borrower is jointly and fully liable for the whole mortgage debt, not a percentage share. This is different from a guarantor, who backstops repayment without any ownership stake.
Joint from the start: co-borrowers typically apply together as intended co-owners, rather than being added later to strengthen a weaker file.
Fully counted in the ratios: a co-borrower’s income and debts are added into GDS and TDS for the whole application, the same as the primary applicant’s.
Jointly and fully liable: each co-borrower is responsible for the entire mortgage debt, not just a proportional share, if the other stops paying.
On title: co-borrowers are registered as legal owners of the property, distinguishing the role from a guarantor.
Definitions reflect Canadian federal and provincial rules as of the “Updated” date above. Not advice for any specific file.
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