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A co-signed mortgage does not necessarily have to remain in the qualifying debt-to-income calculation, but exclusion is not automatic. I start with the applicable program and the evidence showing who has actually made the payments. A family understanding is different from the documentation the lender needs.
The question from the borrower
A retired borrower had co-signed a relative’s mortgage, and the other party had reportedly made the payments for years. The concern was whether that mortgage would consume qualifying room for the borrower’s own financing.
The case notes describe a payment history to investigate, not an underwriter’s final exclusion. I would want the current mortgage documents and acceptable proof of the other party’s payments before building a loan amount around the assumed treatment.
A specific agency path, not a universal promise
For applicable Fannie Mae loans, excluding mortgage debt paid by someone else requires that payer to be obligated on the debt, no delinquencies in the latest 12 months, no use of the property’s rental income to qualify, and the prescribed 12-month payment evidence. See Fannie Mae’s debts-paid-by-others requirements (new tab). The subject property may still affect the financed-property count. Other programs and lender rules need their own review.
Those conditions explain why “they have always paid it” is the beginning of the conversation. It tells us what evidence to request. It does not let us skip the program review or assume that a few recent transfers establish the full history.
Build the file without mixing payment stories
- Identify everyone obligated on the mortgage.
- Confirm what the full housing expense includes.
- Document the required payment period and the actual payer.
- Identify late payments, reimbursements or shared payments that need explanation.
- Tell the lender whether any rental income from the property is being used.
I would ask the lender what format is acceptable before the family spends time gathering records. Mortgage statements may show that payments arrived, while bank records may help show whose funds paid them. The reviewer decides whether the complete evidence supports the requested treatment.
Run both versions while the question is open
Until the exclusion is confirmed, I would compare the qualifying calculation with the obligation included and with it excluded. That shows how much the unanswered question matters. If the purchase or refinance only works after exclusion, the document review becomes an early dependency rather than a last-minute surprise.
The household budget deserves its own version of the same question. If the relative could no longer pay, is the co-signer prepared for that possibility? A favorable underwriting treatment does not necessarily end the borrower’s contractual responsibility for the original mortgage.
Do not confuse exclusion with release
If the lender excludes it from DTI, am I off the old loan? No. Excluding an obligation from a new loan’s qualifying calculation is not a release from the original note. Ask the existing lender about any separate process for changing liability.
That distinction is central to the advice I would give in this situation. We can investigate whether the mortgage belongs in the new qualification calculation while still recognizing the borrower’s existing commitment. Both questions deserve accurate answers.
Start with the fact that you co-signed and who makes the payments. We can identify the right documentation and a secure way to provide it, then show what the verified treatment means for your next move.
Published September 13, 2026. Adapted from an origination discussion I worked through. Identifying details are omitted. Figures describe the discussion or clearly stated calculations, not current loan offers or guaranteed outcomes. Program, property and borrower requirements need an individual review. Nick Cunningham, Loan Officer, NMLS #907393. Mortgage services through Golden Bay Mortgage Group.
