Someone you care about needs a car and can't get approved alone. You're planning to buy a home in the next year or two. Before you sign, it's worth knowing exactly how a mortgage lender will see that signature — because it isn't how most people expect.
Quick answer: Yes, in most cases. A cosigned car loan shows up on your credit report as your debt, and mortgage lenders count its full monthly payment in your debt-to-income ratio even if you never pay a cent. At a 7.18% mortgage rate, every $100 a month of car payment costs you roughly $14,800 of borrowing power, so a typical $525 payment cuts about $77,500 off the mortgage you can get. The exception: once the borrower has made 12 on-time payments from their own account and you can document them, conventional lenders can leave the loan out.
Cosigning makes you legally responsible for the whole loan. The account appears on your credit report with its balance and monthly payment, and an underwriter has no way to know, from the report alone, who actually pays it. So it goes into your debt-to-income ratio — the share of your gross monthly income that goes to debt payments, including the new mortgage.
Most conventional lenders work to a total debt-to-income limit of around 43% to 45%, and Fannie Mae's automated underwriting can go as high as 50% for strong applicants. Whatever the limit, the car payment comes straight out of the room that would otherwise go to your house payment.
Each dollar of monthly debt is a dollar the mortgage payment can't use. At the Freddie Mac 30-year average of 7.18% (November 5, 2026), here's what common car payments cost you:
| Car payment | Mortgage lost | Home price lost (10% down) |
|---|---|---|
| $300/mo | ~$44,300 | ~$49,200 |
| $400/mo | ~$59,000 | ~$65,600 |
| $525/mo | ~$77,500 | ~$86,100 |
| $700/mo | ~$103,300 | ~$114,800 |
A concrete case: $8,000 a month of gross income, $400 of other debts, a 45% limit and $450 a month for taxes and insurance leaves room for about a $406,000 mortgage — a $451,000 home with 10% down. Cosign a $25,000, 60-month loan at 9.5% ($525 a month) and that becomes about $328,000 and $365,000.
If your budget has slack, this may not matter. If you're already stretching to buy in your market, it can be the difference between approval and denial.
Fannie Mae's Selling Guide lets a lender exclude a debt you're obligated on when someone else is paying it — but only with proof. The lender needs the most recent 12 months of canceled checks or bank statements from the person making the payments, showing no late payments. Two practical consequences:
FHA, VA and other loan programs have their own rules for these "contingent" debts, and individual lenders can be stricter, so ask your loan officer before you sign either document.
The new loan brings a hard inquiry and a brand-new account, both of which can nudge your score down for a few months. That's minor. The real risk is a missed payment: it goes on your report exactly as it goes on the borrower's, and a single 30-day late payment can drop a strong score by 60 to 80 points or more — enough to push your mortgage rate up a tier.
If the borrower stops paying and the car is repossessed, the lender sells it, usually at auction, and applies the proceeds to the balance. Experian is clear that the cosigner is equally liable for whatever is left — the deficiency — plus repossession costs, and the repossession stays on both credit reports for seven years.
The shortfall is biggest early in the loan, when the balance is high and the car has just taken its largest depreciation hit. On that $25,000 new-car loan, if payments stopped after six months and the car sold for 80% of its market value, the shortfall would be roughly $6,200 after about $1,200 in fees. After two years, it would still be about $4,000.
Our cosigner risk calculator runs both numbers for your own situation: the home-buying budget you'd give up and what you could owe if the loan goes bad.