Definition
A co-borrower is a person who signs the mortgage contract alongside the primary borrower and assumes joint liability for the loan. Their income is counted in debt ratio calculations (GDS and TDS), which can increase total borrowing capacity. Their credit score is also evaluated.
A co-borrower differs from a guarantor (co-signer): a guarantor does not occupy the property and is only responsible for payments in case of default. The co-borrower may or may not be on the property title, depending on the chosen structure.
Common situations: couples (married, civil union, or common-law), parents co-signing for a child buying a first property, or business partners for an income property. Note: in Quebec, if co-borrowers are not married or in a civil union, the mortgage contract must explicitly state each party's share on the deed of sale.