Debt-to-Income Ratio Rules
Debt-to-Income Ratio Rules
Debt-to-income (DTI) is the lender's formal measure of affordability. Front-end DTI (housing costs) and back-end DTI (all debts) have strict thresholds that determine the maximum home price you can qualify for.
Key takeaways
- Front-end DTI (housing costs ÷ gross income) should not exceed 28% for conventional loans.
- Back-end DTI (all debt ÷ gross income) should not exceed 36% for conventional loans.
- FHA allows up to 50% back-end DTI with "compensating factors" (high reserves, strong credit).
- DTI uses gross income, not take-home; this creates a gap between "approved amount" and "affordable amount."
- Student loans, car payments, credit card minimums, child support, and alimony all count toward DTI; they reduce your qualifying power for a mortgage.
The two DTI ratios
Front-end DTI (housing ratio):
Front-end DTI = (P&I + Property Tax + Insurance + HOA) ÷ Gross Monthly Income
Lender prefers this under 28%.
Back-end DTI (total debt ratio):
Back-end DTI = (Housing costs + All other monthly debt) ÷ Gross Monthly Income
Lender prefers this under 36%.
The lender uses whichever is more restrictive (typically back-end), then often applies the more conservative of the two.
Worked example: Front-end and back-end DTI
Scenario: Combined household income $120,000/year
Gross monthly income: $120,000 ÷ 12 = $10,000
Housing costs (front-end):
- Mortgage P&I: $1,679
- Property tax (1.2% annually on $350,000): $350/month
- Insurance: $120/month
- HOA: $0
- Total PITI: $2,149
Front-end DTI: $2,149 ÷ $10,000 = 21.5% ✓ (under 28%, acceptable)
Other monthly debts (added to back-end):
- Car loan: $350
- Student loan: $200
- Credit card minimum (reported monthly obligation): $100
- Child support: $500
- Total other debt: $1,150
Back-end DTI: ($2,149 + $1,150) ÷ $10,000 = 31.5% ✓ (under 36%, acceptable)
Both ratios pass. You're approved for this home price.
Now add a new car loan ($500/month):
New other debt: $1,150 + $500 = $1,650 New back-end DTI: ($2,149 + $1,650) ÷ $10,000 = 37.99% ✗ (exceeds 36%)
You're no longer approved for this home price. Taking on new debt reduced your qualifying power.
What counts toward DTI?
Always counts:
- Mortgage payment (principal + interest)
- Property taxes
- Homeowner's insurance
- HOA fees
- Auto loans (reported minimum monthly payment)
- Auto leases (monthly payment)
- Student loans (reported minimum monthly payment, or 1% of outstanding balance if payment is deferred)
- Personal loans
- Credit card minimum payments
- Child support / alimony
- Medical debt in collections (if ongoing, may count)
Usually doesn't count:
- Cell phone bills
- Utilities (electric, gas, water)
- Groceries, gas, insurance (auto/health)
- Subscriptions (Netflix, gym)
- Childcare (not always; some lenders count if you have dependents)
- Income-based student loan repayment plans (calculated differently; contact lender)
Gray areas:
- Rental payments: If you're renting now, rent doesn't count toward DTI (it's replaced by mortgage). But if you're moving out of a lease early, you may owe break-up fees.
- Alimony/child support: Counts only if you have a legal obligation.
- Dependent care: Some lenders count if you have childcare expenses; others don't.
The $120k household: Front-end vs back-end constraints
Gross income: $120,000/year = $10,000/month
Maximum front-end DTI (28%): $2,800/month housing Maximum back-end DTI (36%): $3,600/month total debt
If you have $0 other debt:
- Front-end limits you to $2,800/month housing
- On a $280,000 loan at 6% + $350 tax + $120 insurance = $2,149/month, you're well under limit
- Home price supported: ~$380,000 (rough estimate)
If you have $700/month other debt (car + student loan):
- Front-end still allows $2,800/month housing
- Back-end allows $3,600 − $700 = $2,900/month housing
- Back-end is MORE restrictive, so $2,900/month is your max for housing
- Home price supported: ~$420,000 (rough estimate)
If you have $1,200/month other debt (car + student loan + credit cards):
- Front-end allows $2,800/month housing
- Back-end allows $3,600 − $1,200 = $2,400/month housing
- Back-end is MORE restrictive
- Home price supported: ~$350,000 (rough estimate)
As you accumulate other debt, your back-end DTI constraint tightens, reducing how much house you can afford.
Example: How to calculate maximum home price
Inputs:
- Gross annual household income: $100,000 ($8,333/month)
- Existing debts: Car loan $300/month, student loans $200/month
- Available down payment: $50,000
- Target rate: 6%, 30-year term
- Estimated property tax: 1.2% annually
- Estimated insurance: $120/month
Step 1: Calculate back-end DTI constraint
- Maximum total debt: $8,333 × 36% = $3,000/month
- Current monthly debt: $300 + $200 = $500
- Available for housing: $3,000 − $500 = $2,500
Step 2: Allocate housing budget
- Available PITI: $2,500/month
- Property tax and insurance: Estimate $120 + (home value × 1.2% ÷ 12)
- For a $300,000 home: $120 + $300 = $420
- Available for P&I: $2,500 − $420 = $2,080
Step 3: Back-solve for loan amount
- Monthly P&I at 6%, 30-year: $1,679 per $280,000
- If you can afford $2,080/month: ($280,000 ÷ $1,679) × $2,080 = $346,000 loan
Step 4: Home price
- Loan: $346,000
- Down payment: $50,000
- Home price: $396,000
You can afford a home around $396,000 at this income and debt level.
Improving DTI: Strategies before buying
1. Pay down credit cards
- Credit card balances reduce available DTI.
- Paying off a credit card (or paying down the balance significantly) lowers the minimum payment.
- Example: Credit card with $15,000 balance and 2% minimum = $300/month payment. Pay it off, save $300/month in DTI capacity.
2. Pay off car loans or student loans
- Waiting to buy until a major debt is paid off can increase your qualifying power significantly.
- Example: Pay off car loan ($350/month), suddenly your back-end DTI improves by 3.5% ($350 ÷ $10,000).
3. Increase income
- Spousal income: If one spouse isn't working, adding spousal income increases qualifying power by up to 50%.
- Promotion / raise: A $10,000/year raise adds $83/month to gross income, allowing ~$30/month more in housing.
- Second job: Income must be documented (usually 2-year average required).
4. Delay major purchases
- Don't buy a car or open new credit cards 3–6 months before buying a home.
- New debt immediately reduces DTI and can disqualify you.
DTI and loan type: Different thresholds
Conventional loans:
- Front-end: 28% (strict guideline; some lenders go to 29–30%)
- Back-end: 36% (strict guideline; Fannie Mae/Freddie Mac allow up to 43% for "QM" qualified mortgages)
FHA loans:
- Front-end: 31% (slightly higher)
- Back-end: 43% (strict guideline; can go to 50% with "compensating factors")
VA loans:
- Front-end: Not strictly applied
- Back-end: 41% (though some VA lenders are more lenient with strong reserves)
FHA and VA allow higher DTI because they carry insurance (FHA/VA mortgage insurance protects lender). Conventional is stricter.
"But I was approved for more..."
Lenders often pre-approve you for MORE than is prudent. A pre-approval letter for $500,000 on a $80,000 income is technically possible (at 43% back-end DTI with no other debt), but it's dangerous.
A safer rule: Keep your own personal front-end DTI under 25% of gross income (vs. lender's 28%), and back-end under 35% (vs. lender's 36%). This creates a buffer for emergencies and lifestyle changes.
Example: $100,000 income.
- Lender says: Approve up to $2,800/month housing (28%)
- You should target: $2,083/month housing (25%)
- Difference: $716/month extra capacity for life's surprises
Worked example: DTI before and after paying off debt
Before:
- Income: $120,000/year ($10,000/month)
- Car loan: $350/month
- Student loan: $200/month
- Credit cards: $100/month
- Other debt: $650/month
- Back-end DTI available: $3,600 − $650 = $2,950/month for housing
- Home price estimate: ~$420,000
After (paying off car loan and credit cards, only student loan remains):
- Income: $120,000/year ($10,000/month)
- Student loan: $200/month
- Other debt: $200/month
- Back-end DTI available: $3,600 − $200 = $3,400/month for housing
- Home price estimate: ~$480,000
By paying off $450/month in other debt, you increased qualifying power by ~$60,000 in home price. This is why eliminating debt before buying is powerful.
Decision tree
Next
You know your DTI and qualifying power. But the rate you get depends on one more factor: your credit score. The same $300,000 loan might cost 5.5% at 780 credit or 7.5% at 640 credit. Understanding credit score thresholds is crucial.