Debts paid by someone else
Being legally obligated on a debt does not always mean the payment must stay in the borrower's DTI.
Fannie non-mortgage debt
Fannie can exclude qualifying non-mortgage debts when another party has actually made the payments, subject to documentation and the interested-party restriction.
Fannie mortgage debt
For a mortgage payment to be excluded, Fannie requires additional conditions, including that the person making the payments is also obligated on the mortgage debt and the payment history satisfies the applicable rule.
Freddie
Freddie similarly allows installment, revolving and lease debt to be excluded when another party has made timely payments for the required history; mortgage debt has extra requirements and the paying party must be obligated on the Note.
Official guide baseline
Fannie Mae Selling Guide · Freddie Mac Seller/Servicer Guide
Debt treatment can change with documentation, remaining term and AUS feedback. Current agency guide controls.