If credit score is the gate, DTI is the seatbelt — every loan approval has both. A 780 score with a 50% DTI gets the same denial as a 600 score most of the time. Understanding the math before you apply prevents the surprise.
The two ratios
Front-end DTI (sometimes called the "housing ratio") is the proposed monthly housing payment divided by gross monthly income. It includes:
- Principal + interest on the new mortgage
- Property tax (estimated annual amount divided by 12)
- Homeowner's insurance (annual divided by 12)
- HOA dues if applicable
- Mortgage insurance (PMI on conventional with under 20% down, MIP on FHA, funding fee on VA)
That sum is PITI(A) — Principal, Interest, Taxes, Insurance (and Association dues / mortgage insurance if applicable). PITI(A) ÷ gross monthly income = front-end DTI.
Back-end DTI is PITI(A) plus all other monthly debt obligations, divided by gross monthly income.
What counts in "other monthly debt":
- Minimum payments on credit cards (lender uses the higher of statement minimum or 1% of balance)
- Auto loan payments
- Student loan payments (income-driven plan amount or 0.5% of balance, depending on loan type and lender)
- Personal loan payments
- Child support, alimony, court-ordered payments
- Any installment loan with 10+ remaining payments
What does NOT count:
- Utilities (electric, water, internet)
- Cell phone bill
- Insurance you pay yourself (auto, renters, life)
- Subscriptions
- Groceries / food
- Gym memberships, streaming services, entertainment
It's specifically debt-to-income, not expense-to-income. This is why people are often surprised that a $400/month childcare bill doesn't affect mortgage qualification — childcare isn't debt, it's an expense.
The thresholds by loan program
Conventional (Fannie Mae / Freddie Mac)
The classic 28/36 rule:
- Front-end DTI: 28% (some programs allow 25%)
- Back-end DTI: 36% (some programs allow up to 45% with compensating factors like high credit score, large reserves, low LTV)
Conventional underwriting via Fannie's automated system (DU — Desktop Underwriter) and Freddie's (LPA — Loan Product Advisor) can approve back-end DTIs up to ~50% in narrow circumstances when the rest of the file is exceptional.
FHA
The 31/43 rule:
- Front-end: 31%
- Back-end: 43%
With "compensating factors" (significant reserves, low LTV, strong residual income, minimal credit obligations), FHA can approve up to 50% back-end DTI. This is the safety net that makes FHA the lane for higher-DTI borrowers who can't qualify conventional.
VA
VA primarily uses back-end DTI of 41% as the headline guideline, but the actual decision rests on residual income (what's left after all debts and basic living expenses are paid). VA allows back-end DTI well above 41% if residual income easily clears the regional baseline. Many VA approvals at 50%+ DTI happen because residual was strong.
USDA
USDA rural loans use 29/41 as the standard ratios, similar to FHA but slightly tighter on the front-end.
The income side: what counts as "gross monthly income"
For mortgage purposes, your income is averaged in a specific way:
W-2 employees: Year-to-date pay divided by months elapsed, averaged with prior year(s). Bonus income generally requires a 2-year history to count.
Self-employed: Net income from Schedule C (after deductions), averaged over the last 2 years per Fannie Mae guidelines. This is the brutal one — every deduction you took to reduce taxable income now reduces your qualifying income. Many self-employed buyers find their qualifying income is half what their gross revenue suggests. (See also the 2-year self-employment rule and exceptions.)
Retirement / Social Security: Allowed if the income will continue at least 3 years from the loan closing date. Documentation required.
Rental income: 75% of gross rental income (the 25% haircut accounts for vacancy + maintenance) if documented on tax returns. New rental properties without history have stricter rules.
Gift income / family support: Generally does NOT count.
The math: a worked example
Buyer profile:
- Gross income: $90,000/year ($7,500/month)
- Looking at a $400,000 home with 10% down
- Estimated PITI(A): $2,800/month
- Existing debt: $300/month auto loan + $150/month minimum on credit cards + $200/month student loan = $650
Front-end DTI: $2,800 / $7,500 = 37.3% Back-end DTI: ($2,800 + $650) / $7,500 = $3,450 / $7,500 = 46%
This buyer:
- Fails conventional 28/36 on both ratios
- Fails FHA 31/43 on both ratios
- Could potentially qualify FHA with compensating factors (back-end up to 50% allowed in DU/LPA)
- Is well outside VA without strong residual income
If they want conventional, they need to either:
- Increase income (raise/promotion) or document additional income (rental, side gig with 2-year history)
- Pay off the auto loan (or refinance to a smaller balance with longer term — caution: the new term must be 10+ months remaining for the payment to count)
- Lower the target home price to reduce PITI(A)
Where most people miscalculate their own DTI
Three common errors:
1. Using net income (take-home) instead of gross. Net is what's left after taxes, 401k, insurance. Lenders use gross. This shifts the percentage by 25-35% wider than people estimate.
2. Forgetting tax + insurance. People estimate "my mortgage will be $2,000" based on principal + interest only. Then property tax + homeowner's insurance + PMI add another 20-30% to the actual PITI. A $2,000 P&I in many areas means $2,500-2,800 PITI(A).
3. Using current credit card balance instead of minimum payment. Lender uses the higher of statement minimum or 1% of balance. Someone with $30K in credit card debt at 2% minimums has $600/month counting toward DTI — even if they pay $1,500/month and are paying the cards down. The reported minimum is what matters.
How to lower DTI quickly
Score-improvement is slow. DTI improvement can be fast.
Pay off small balances entirely. A $4,000 auto loan with $300/month payment removed from DTI is worth more than a $30,000 student loan payment reduction. Killing payments is more powerful than reducing them, because anything 10+ months remaining still counts.
Pay down credit cards aggressively. Drops the 1%-of-balance minimum the lender will use. $20K paid down to $5K drops the lender's calculated minimum from $200 to $50, freeing $150/month in DTI capacity.
Consolidate or refinance. If you have a $400/month auto loan with 24 months left, refinancing to 60 months might drop the payment to $180. The payment counts, not the underlying debt — so the DTI improves.
Wait to apply. If the auto loan has 8 months left, it doesn't count toward DTI per Fannie/Freddie rules (under 10 months). Sometimes the right move is to wait 2 months and apply when the auto debt becomes "non-counting."
Where Paliscore fits
The DTI calculator inside Paliscore (Starter+ tier) takes your reported income and existing debts and shows you the front-end and back-end DTI for conventional, FHA, and VA simultaneously, with the specific PITI(A) you can support at each band. The readiness brief flags DTI as a priority when it's the binding constraint, before it becomes a denial at application time.
Take the quiz — 2 minutes to see your DTI position.
Related reading
- Mortgage reserves — what counts as cash reserves
- How fast can you drop credit utilization 20 points?
- Self-employed mortgage prep: tax transcripts
- The two-year self-employment rule for mortgage
- Which FICO version mortgage lenders actually use
Sources
- Fannie Mae Selling Guide, B3-6-02 (DTI ratios) — Fannie Mae documentation portal
- Freddie Mac Single-Family Seller/Servicer Guide, Section 5401.2
- HUD FHA Single-Family Handbook 4000.1, Section II.A.5.d
- VA Lender's Handbook, Chapter 4 (DTI + residual income tables)
- USDA Single Family Housing Guaranteed Loan Program 7 CFR Part 3555
DTI thresholds and underwriting overlays change frequently. Verify current limits with your specific lender before relying on the numbers in this article.