When a husband and wife are qualifying as borrower and co-borrower many lenders will use the lowest middle score to qualify them for a particular program. This is why it's important to keep your scores as high as possible.

The borrower on the loan is the one with the highest income however co-borrowers are equally responsible for the mortgage payments as well.

There are some lenders that have loan programs that will use the score of the co-borrower.

Having a co-borrower on the loan often may be the difference between qualifying or being denied for a loan.