When people ask this they are usually hoping that the answer will be in their favor. They want to know if the lender will average the scores or use just one? They would like to hear the lender will use the higher one or even the highest possible one.
Everyone has three credit scores, one from each of the three major credit reporting bureaus: Experian, TransUnion, and Equifax. The lender will take the middle score that each person has, not the average, but the one in the middle of the three. Now each person has one credit score and the lender will take the lower of the two.
So if Borrower A has three scores – 680, 700, and 710 – and Borrower B has three scores – 820, 780, and 800, the lender will have 700 for Borrower A and 800 for Borrower B. The credit score used for the joint mortgage application will be 700, because it is the lower of the two middle scores.
Sometimes if one of the borrowers has a very low score, the other borrower might try to buy alone. This can only work if that borrower can support the mortgage on their own income. If the lender is not taking into consideration a borrower’s score, the lender won’t use the income either.