How to Calculate DTI for Mortgage Approval

As a mortgage underwriter, the first number I look at when a loan file lands on my desk isn't your credit score — it's your debt-to-income ratio (DTI). A 780 FICO score won't save a file where the DTI is 56%, and a 680 score can absolutely close on time when the DTI is clean. DTI tells me, in a single ratio, whether you can realistically absorb a new housing payment on top of your existing obligations. If you're preparing to apply in 2026, here's exactly how to calculate DTI for mortgage approval — the way a lender will.

What Is DTI?

Your debt-to-income ratio is your monthly debt payments divided by your gross monthly income:

DTI = Monthly Debt Payments ÷ Gross Monthly Income

For mortgages, lenders compute two ratios, not one:

• Front-end ratio (housing ratio) = PITI ÷ gross monthly income
• Back-end ratio (total debt ratio) = (PITI + all other debt) ÷ gross monthly income

PITI is your Principal, Interest, property Taxes, and Insurance — and for most loans we also include HOA dues and, where applicable, mortgage insurance, giving us PITIA. The front-end ratio isolates housing; the back-end ratio captures your total monthly debt burden. Both must clear the lender's thresholds.

DTI Limits by Loan Type (2026)

Each loan program sets its own DTI ceiling. The numbers below reflect the governing guides in effect for 2026 originations.

A critical point: these are maximums, not targets. Files at the ceiling need compensating factors — strong reserves, high credit scores, or stable residual income — to get an approve/eligible decision.

How to Calculate DTI

Step 1: Determine Gross Monthly Income

Use income before taxes. For a W-2 borrower, that's annual salary ÷ 12. For variable income (bonus, commission, self-employment), we average the most recent two years.

Step 2: List All Monthly Debt Payments

Include:

• New mortgage payment (PITIA) — principal, interest, taxes, insurance, HOA
• Revolving debt — use the minimum payment on the credit report, not what you actually pay
• Installment loans — auto, student, personal
• Child support and alimony — paid, not received

Do not include:

• Utilities (electric, gas, water, internet)
• Cell phone
• Insurance premiums (non-housing)
• Gym, subscriptions, streaming services
• Groceries, gas, childcare

Note on deferred student loans: Even if payments are deferred, we typically count them at 1% of the outstanding balance or the fully amortized payment — per Fannie Mae Selling Guide B3-6-05.

Step 3: Calculate the Ratios

Divide PITI by gross monthly income for the front-end. Add all other debt to PITI and divide by gross monthly income for the back-end. Multiply by 100 to express as a percentage.

Worked Example

Borrower profile:

• Annual salary: $75,000 → $6,250 gross monthly income
• Proposed mortgage PITI: $1,800
• Car payment: $400
• Student loan: $300
• Credit card minimums: $150
• Total monthly debt: $2,650

Front-end DTI:

$1,800 ÷ $6,250 = 0.288 = 28.8%

Just over the 28% conventional front-end limit.

Back-end DTI:

$2,650 ÷ $6,250 = 0.424 = 42.4%

Over the 36% conventional back-end limit, but under the 43% FHA limit.

Underwriter's verdict: This file will not receive a conventional approve/eligible from Fannie Mae's Desktop Underwriter at standard thresholds. It may qualify for FHA under Handbook 4000.1 — particularly if reserves, rent history, or residual income provide compensating factors. Want to run your own scenario? Use our DTI Calculator to model it in seconds.

Income Sources That Count

Not all income is qualifying income. Here's what underwriters can use:

• W-2 wages — need a 2-year history, current pay stubs, and W-2s
• Self-employment income — 2-year average of net business income (from tax returns, not bank deposits)
• Bonus and overtime — 2-year history, documented as likely to continue
• Commission — 2-year average
• Rental income — 75% of gross rent (we apply a 25% vacancy/maintenance allowance)
• Investment income — must be likely to continue for 3+ years
• Alimony/child support (received) — must continue 3+ years past loan term
• Social Security and pension — grossed up by 25% if non-taxable (so $2,000/mo tax-free counts as $2,500)

Debts That Count vs. Don't

Count Toward DTI

• Mortgage and HELOC payments
• Auto, student, and personal loans
• Credit card minimum payments
• Child support and alimony (paid)
• Co-signed loans (unless you can prove someone else paid them for 12+ months)

Don't Count Toward DTI

• Utilities (electric, water, gas, internet)
• Non-housing insurance premiums
• Cell phone
• Gym and subscriptions
• Groceries, gas, childcare

Deferred Loans

Deferred student loans are the #1 reason borrowers get blindsided at underwriting. Fannie Mae typically uses 1% of the balance unless you can document the actual amortizing payment. Freddie Mac Seller Guide Section 5401.2 allows the lesser of 1% or the amortized payment. FHA uses 1% unless the credit report shows a fixed payment. Always clarify this with your loan officer before applying.

How to Lower Your DTI

If your ratios are over the limit, here are the levers — in order of impact:

1. Pay off debt — target the highest monthly payment first to free up the most DTI room
2. Increase income — side income must be 2-year stable to count; recent raises generally won't qualify until reflected on a W-2
3. Add a co-borrower — their income and debts enter the ratio together
4. Lower the purchase price — directly reduces PITI
5. Make a larger down payment — smaller loan = smaller payment
6. Refinance existing debt to a longer term — lowers the monthly payment that counts against DTI
7. Use gift funds to pay off debt — gift letters must document no repayment is expected

A practical tip: paying down a credit card to lower its minimum payment is faster and cheaper than waiting for a raise. Our Debt Payoff Calculator shows exactly how much DTI room you reclaim per dollar paid down.

Common DTI Mistakes

I see these on loan files every week:

• Using net income instead of gross — lenders use gross, always. If you've been budgeting on take-home, your DTI math is off.
• Including utilities in DTI — utilities are living expenses, not debts. Don't add them.
• Forgetting deferred student loans — they count even when deferred. See above.
• Applying for new credit before closing — a new car loan or credit card can push DTI over the limit and derail a clear-to-close. Freeze new credit applications from application through closing.
• Co-signing for someone else's loan — it shows on your credit report and counts against your DTI unless you can document 12 months of payments made by the primary borrower.

Bottom Line

DTI is the gatekeeper of mortgage approval. Know your two ratios before you apply, know which loan program fits your numbers, and clean up the variables you can control — pay down balances, avoid new credit, and document income thoroughly. A borrower who walks in with a clean DTI calculation closes faster, gets better terms, and avoids the most common underwriting conditions. Run your numbers first with our DTI Calculator, then map the resulting payment to a home price with the Mortgage Calculator and the Affordability Calculator.

Next Steps

• DTI Calculator — compute your front-end and back-end ratios in under a minute
• Mortgage Calculator — estimate PITI for the home you're considering
• Affordability Calculator — reverse-engineer the max home price your DTI supports
• Debt Payoff Calculator — see how paying down debt lowers your DTI
• Credit Card Payoff Calculator — target the revolving balances dragging your ratio
• FHA Calculator — model an FHA scenario when conventional DTI is too tight

Sources

• Fannie Mae Selling Guide B3-6-01 (Liability Assessment) and B3-6-05 (Monthly Obligations)
• Freddie Mac Seller Guide Section 5401 (Liabilities) and 5401.2 (Monthly Debt Payment)
• FHA Handbook 4000.1, Section II.A.4 (Liabilities) and II.A.5 (Income Analysis)
• VA Lenders Handbook (VA Pamphlet 26-7), Chapter 4 (Credit Underwriting) — residual income standards
• Consumer Financial Protection Bureau — "What is a debt-to-income ratio?" consumer guidance
• USDA Guaranteed Underwriting System (GUS) and HB-1-3555 Chapter 9 (Income Analysis)