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The two DTI numbers lenders care about.

Every mortgage lender calculates two separate DTI ratios for every application. The front-end ratio (also called the "housing ratio" or "PITI ratio") divides your proposed monthly housing payment — including principal, interest, property taxes, homeowner's insurance, and HOA fees if applicable — by your gross monthly income.

The back-end ratio divides the sum of all your minimum monthly debt payments — housing plus car loans, student loans, credit card minimums, personal loans, child support, alimony, and any other recurring obligations — by your gross monthly income. The back-end ratio is the one that most often determines whether you get approved, and at what rate.

Why DTI matters more than credit score alone.

A high credit score tells a lender you've paid your bills on time in the past. DTI tells them whether you'll be able to continue paying them after adding a mortgage to the mix. A borrower with a 780 credit score and a 55% DTI may actually be a higher lending risk than a borrower with a 680 score and a 32% DTI — because cash flow determines whether the payment gets made each month.

Lenders use both, of course. But DTI is the ratio that directly limits loan size — it's the number that determines how much house you can buy. Credit score primarily affects the interest rate you'll be offered. DTI affects whether you qualify at all, and for how much.

The math behind DTI.

The formulas are simple — the tricky part is knowing which numbers go in.

Key points: "gross income" means before taxes — never use your take-home pay. "Monthly debts" means minimum required payments only, not what you actually pay. If you're paying $500/month on a credit card with a $35 minimum, lenders use $35, not $500. And "housing payment" for a mortgage application should include the proposed PITI (principal, interest, taxes, insurance) — not your current rent. Use our affordability calculator to model the full payment before entering it here.

How lenders use DTI to approve your loan.

When your mortgage application goes into underwriting, the processor pulls your credit report to find every monthly obligation, adds up the minimums, adds your proposed housing payment, and divides by your verified gross income from pay stubs and tax returns. That final number gets compared against the program's DTI limits.

If you're above the limit, the underwriter may ask for explanations or compensating factors — a large down payment, significant reserves, a high credit score, stable long-term employment, or the absence of any late payments. If none of those offset the high DTI, the loan gets denied or the loan amount gets reduced until the DTI falls within guidelines. Buyers using Beycome's buyer program can apply their up-to-2% commission credit directly toward the down payment — a real compensating factor.

This is exactly why running this calculator before you apply — not after — gives you an enormous advantage. You'll know your DTI position before a lender does, and you'll have time to improve it. Getting pre-qualified or preapproved early helps you understand exactly where you stand.

What the rule is.

The 28/36 rule states that a household should spend no more than 28% of its gross monthly income on housing costs and no more than 36% on total debt. These numbers originated from decades of mortgage default analysis — statistically, households with a back-end DTI above 36% begin experiencing noticeably higher rates of financial stress, late payments, and eventual default. The 28% front-end limit ensures that housing alone doesn't crowd out other financial priorities.

In a practical sense, the 28/36 rule is the "ideal range" that every mortgage professional knows. Staying within it signals to any lender that you're a low-risk borrower. It also means you likely have meaningful room in your budget to handle unexpected expenses — job loss, medical bills, home repairs — without missing a mortgage payment.

When lenders go higher.

In practice, most lenders will approve borrowers well above 36% on the back end. Fannie mae and Freddie mac allow conventional loans up to 43% back-end DTI automatically, and up to 50% when the application clears their automated underwriting engines (Desktop Underwriter for Fannie, Loan Prospector for Freddie). FHA allows up to 50% back-end with compensating factors. VA loans use a residual income test rather than a hard DTI ceiling. The CFPB explains why the 43% threshold matters for qualified mortgage rules.

The compensating factors that give lenders room to stretch include: a credit score above 720, a down payment of 20% or more, significant liquid reserves (six or more months of mortgage payments in the bank), long-term stable employment, and no payment history of late payments. The more of these you have, the more flexibility an underwriter can apply.

When lower is required.

For jumbo loans — mortgages above the conforming loan limit (currently $806,500 in most of the US for 2025) — most lenders require back-end DTI of 43% or below, and many prefer 36% or less. Jumbo loans are held on bank portfolios rather than sold to Fannie or Freddie, so the lender takes on the entire default risk. That makes them significantly more conservative.

Similarly, investment properties typically require lower DTI than owner-occupied homes, because rental income is only partially counted (often at 75%) and the perceived risk is higher. If you're applying for a second home or investment property, aim for a back-end DTI well below 43% — ideally under 36% — to have the smoothest path through underwriting.