When a lender evaluates a mortgage application, they aren't asking "how much house can this person afford" in the abstract — they're checking whether the specific loan being requested clears two numeric thresholds: the front-end ratio and the back-end ratio. This calculator runs the same check, from the buyer's side, before you ever talk to a loan officer.
Framing it as a qualification check rather than a price search changes what you look at. Instead of asking "what's my max price," the useful question becomes "does this specific loan amount clear both ratios, and if not, which one is the problem?" — because that's exactly what determines whether an application gets approved, and at what terms.
What underwriters actually check
Front-end ratio: your proposed monthly housing payment (principal, interest, property tax, homeowners insurance, PMI/MIP, and HOA if applicable) divided by gross monthly income. Conventional lenders typically want this at or below 28%; FHA allows up to 31%.
Back-end ratio: the same housing payment PLUS every other recurring monthly debt obligation reported on your credit report — auto loans, student loans, credit card minimum payments, personal loans, even co-signed debt in many cases — divided by gross monthly income. Conventional lenders typically cap this at 36%; FHA allows up to 43%, and some automated underwriting systems approve exceptions above that with strong compensating factors (large reserves, high credit score, low loan-to-value).
Why the loan amount, not just the price, is what gets underwritten
A mortgage application is underwritten against the loan amount and the resulting payment — not the sale price directly. That's why this calculator solves for maximum LOAN capacity first (via the DTI caps) and then adds back your down payment to arrive at a maximum PRICE. If you're comparing this tool's output to a lender's pre-qualification letter, make sure you're comparing loan amounts and payments, not just headline prices, since down payment size shifts the two.
One qualification detail this calculator does not model: credit score. DTI ratios determine capacity, but your interest rate — which directly drives your monthly payment and therefore your DTI — is set by credit score, loan-to-value, and loan program. Run this calculator with the rate a lender has actually quoted you, not an assumed market average, for the most accurate qualification estimate.
Frequently asked questions
What DTI do I need to qualify for a mortgage?
Conventional loans typically require a front-end ratio at or below 28% and a back-end ratio at or below 36%, though some lenders approve exceptions with strong compensating factors. FHA loans allow up to 31% front-end and 43% back-end.
What's the difference between front-end and back-end DTI?
Front-end DTI counts only housing costs (mortgage principal, interest, taxes, insurance, PMI, HOA) against gross income. Back-end DTI adds every other monthly debt payment on top of housing costs. Lenders check both; whichever is tighter for your situation determines your actual qualifying loan amount.
Does this replace a mortgage pre-approval?
No. This is a DTI-based estimate using your entered assumptions. Actual pre-approval also factors in credit score (which sets your rate), employment verification, asset documentation, and specific lender overlays that vary by institution. Use this to understand your realistic range before applying, not as a substitute for a real pre-approval letter.
Can I qualify for a mortgage with a high back-end ratio?
Some lenders and loan programs (particularly FHA, and conventional loans with automated underwriting approval) allow back-end ratios above the standard 36–43% range for borrowers with strong compensating factors — high credit score, significant cash reserves, or a low loan-to-value ratio. This varies significantly by lender.
Worked examples
Worked example 1
The underwriter's checklist, applied
$120,000 income, $400/mo other debts, $35,000 down, 6.5% rate.
Max home price
$376,579
Binding constraint
front
PMI
$171/mo
Loan amount $341,579 clears both DTI caps at $376,579 home price — the same check an underwriter runs, from the buyer's side.
What affects the result
Loan amount vs sale price
Underwriting evaluates the loan, not the price directly — down payment is what bridges the two.
Credit-score-driven rate
Not modeled directly here — run this calculator with your actual quoted rate, not a market average, for the closest qualification estimate.
More questions answered
Do lenders check front-end and back-end DTI the same way this calculator does?
Yes, in principle — conventional and FHA underwriting both apply front-end and back-end DTI caps. Actual lenders also layer on credit-score-based pricing, specific program overlays, and full income/asset verification that this self-estimate does not include.
Model assumptions & disclosures
Not a pre-approval. This calculator estimates your maximum home price using standard debt-to-income (DTI) caps against the income, debts, rate, and down payment you enter. It does not verify income, assets, credit, or employment, and it is not an offer or commitment from any lender. Actual mortgage pre-approval requires full lender verification and may differ from this estimate.
DTI caps are lender-dependent. The 28/36 (conventional) and 31/43 (FHA) caps used as defaults are common industry guidelines, not universal rules. Individual lenders, loan programs, and automated underwriting systems can approve — or require — different ratios based on credit score, cash reserves, loan-to-value, and other compensating factors not modeled here.
Rate, tax, insurance, and PMI are your estimates, not live data. This calculator never fetches a current mortgage rate, your actual local property tax rate, or a real insurance quote. Defaults are reasonable national approximations — enter your own numbers, or figures a lender or insurer has actually quoted you, for an accurate result.
Credit score is not modeled. Your interest rate — which directly drives your monthly payment and therefore your DTI — depends on your credit score and the specific loan program. This calculator assumes whatever rate you enter; it does not estimate what rate you would actually qualify for.
Not financial or legal advice. This calculator provides illustrative estimates based on your inputs. It does not account for your complete financial picture, local market conditions, or individual circumstances. Consult a qualified mortgage lender, financial advisor, or housing counselor before making a home-purchase decision.