October 1, 2026 Mortgage Rates: DTI Headroom

Freddie Mac’s October 1, 2026 mortgage rates release put the 30-year fixed average at 7.28%, up from 7.03% a week earlier. On a hypothetical $400,000 loan over 30 years, that change adds $67.58 to monthly principal and interest. With $10,000 in qualifying monthly income and all other inputs unchanged, total debt-to-income (DTI) rises about 0.68 percentage points.

For a preapproval near its applicable DTI limit, that increase can consume much of the remaining headroom. These calculations illustrate the effect of a benchmark change; they are not a loan quote or approval decision.

What changed in the October 1 PMMS release?

The 30-year increase was 0.25 percentage points, or 25 basis points, from September 24. The 15-year fixed average also rose, from 6.42% to 6.60%, an increase of 18 basis points. The dated release focuses on conventional, conforming purchase mortgages for borrowers with excellent credit and 20% down. That borrower and loan profile limits how directly the averages apply to an individual preapproval.

Under Freddie Mac’s Thursday-through-Wednesday collection schedule, the October 1 report covers September 24–30 application activity. The Primary Mortgage Market Survey (PMMS) uses applications submitted through Loan Product Advisor. It reports a weekly average rather than a Thursday price sheet, as Freddie Mac’s methodology explanation, published November 3, 2022, describes.

Our mortgage-rate data and reports provide the series context; broader mortgage-rate coverage explains related developments.

Isolate the payment effect of the rate change

Consider a hypothetical household with a $400,000, fully amortizing, 30-year fixed mortgage and $10,000 in gross monthly income accepted for qualification. Hold other qualifying debt payments at $1,100, property taxes at $500, and homeowners insurance at $150 a month. Assume no mortgage insurance, association dues, flood insurance, subordinate loan, or other housing charges.

Only the interest rate changes between the two scenarios:

These are our calculations using 360 monthly payments, with full precision retained until results are rounded for display. Because every other input stays constant, the $67.58 payment increase flows entirely into total obligations.

Fannie Mae’s DTI guidance defines the ratio using monthly qualifying obligations and income accepted for qualification. For this illustration:

Total DTI = (housing expense + other qualifying debt payments) ÷ qualifying monthly income × 100.

The denominator is the income used in underwriting, which can differ from a household’s stated earnings.

Use the mortgage payment calculator to reproduce the principal-and-interest comparison, keeping the balance and term unchanged. Then carry each result into the full DTI calculation.

Measure how much DTI headroom the increase uses

For this example only, assume the lender has established a 45% total-DTI ceiling. This is an illustrative assumption, not a universal lending rule. Fannie Mae’s DTI provisions differ by underwriting method and transaction, and lenders can apply more conservative practices. Fannie Mae’s guidance describes those distinctions.

At $10,000 of qualifying monthly income, the assumed ceiling allows $4,500 in monthly obligations:

• Before: $4,500 minus $4,419.27 leaves $80.73 of monthly headroom.
• After: $4,500 minus $4,486.85 leaves $13.15.

The rate change consumes about 84% of the original headroom, even though DTI rises by less than one percentage point. The file remains below the assumed ceiling, but with little room left for additional obligations. That remaining headroom does not establish eligibility.

To calculate the change in the ratio directly, use:

DTI increase in percentage points = added monthly payment ÷ qualifying monthly income × 100.

Here, $67.58 ÷ $10,000 × 100 is approximately 0.68.

Keep property costs in the qualifying payment

Taxes and homeowners insurance remain in both columns. For an actual property, also include applicable mortgage and flood insurance, association dues, special assessments, ground rent, co-op fees, and subordinate financing payments. Exclude utility charges attributable to individual units from association dues, and deduct the borrower’s allocated individual-unit utility charges from co-op fees. Fannie Mae identifies these components in its monthly housing expense requirements.

Holding an estimate constant isolates the rate effect; it does not establish that the estimate is accurate. A different property’s taxes or association dues can use the remaining headroom independently of rates. Confirm the property-specific costs before relying on the result.

Have the lender rerun the actual file

Replace the benchmark with the file’s actual qualifying rate. For Fannie Mae fixed-rate loans, qualification uses the note rate; a temporary buydown does not substitute its reduced rate. See the qualifying payment requirements.

Recalculation and formal resubmission are distinct. For Desktop Underwriter (DU), Fannie Mae’s automated system, an interest-rate increase requires resubmission when recalculated DTI newly exceeds 45%, or increases by at least three percentage points while remaining at or below 50%. Those are resubmission triggers, not assurances of approval. Fannie Mae’s DU tolerance rules govern that determination.

Before relying on an existing preapproval for an offer, ask the lender for the updated payment, accepted income and debts, revised DTI, applicable limit, and any required underwriting action. Those file-specific figures establish how much qualifying headroom remains.