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Co-Signer vs. Co-Borrower
First of all, I will address a small confusion in terminology in your question. You referred to your mother-in-law as a potential co-signer, when she would actually be a co-borrower.
A co-borrower is someone who is included on the loan application. The co-borrower's income and credit history are used to qualify for the loan and the co-borrower's name will also be listed on the title of the property.
In general, home loans do not accept co-signers on a loan, as opposed to car loans or student loans. Mortgage loans require co-borrowers instead of co-signers.
A co-borrower is different that a co-signer. While a co-signer assumes full responsibility for the debt, in the event that the borrower defaults on the loan, the co-signer does not necessarily have ownership in the property. Co-borrowers are frequently spouses, relatives, or partners. Their income is combined with the borrower, in order to qualify for a larger mortgage than could be obtained without the co-borrower and the co-borrower ends up as a co-owner of the property.
FHA Loans Require Family Relationship For Co-Borrower
There is no requirement that I am aware of that requires a co-borrower on most mortgages to be related by blood. However, the FHA Government Loan Program does require that co-borrowers be related by blood or marriage.
Occupying Co-Borrower vs. Non-Occupying Co-Borrower
It is important to know if the co-borrower will reside in the house or not. Assuming that your mother-in-law will not occupy the house with you, she will become a non-occupying co-borrower. In this case, the lender will use her credit score to help you qualify; however, you as the primary borrower, must be able to qualify with your debt-to-income ratio. In other words, your income alone must be enough to cover the payment -- your lender will generally require that the mortgage payment, including taxes and insurance be no more than 33% of your gross income. So if you can qualify with your income, then it will be beneficial to have her co-sign on the mortgage with her higher credit score.
Co-Borrower is Fully Responsible for Payment
A co-borrower is an equal party on the loan, fully responsible for the payment of the loan and also vested in the property's title. This is unlike a co-signer on other kinds of loans, who guarantee payment in case the primary borrower defaults. Both co-borrowers and co-signers assume considerable liability.
If a person agrees to be a co-borrower, he or she should consider making an agreement with the primary borrower that when the primary borrower's financial picture and credit score improves, the primary borrower will refinance the loan to remove the co-borrower.
Understand the Risks of Co-Signing
Although your question, as I discussed, is really about co-borrowing, I think it is important for me to make a couple of important general comments about co-signing. Anyone considering co-signing on any kind of loan should fully understand the risks and obligations that go along with co-signing for a loan.
It may also be useful to review How Do I Remove My Self as a Co-signer on a Mortgage?, to learn more.
Whenever shopping for a mortgage, makes sure to visit the Bills.com Mortgage Resource Center.
I hope this information helps you Find. Learn & Save.