Front-End vs. Back-End DTI, Explained

When a lender talks about your debt-to-income ratio, they are usually talking about two numbers at once. There is a front-end ratio and a back-end ratio, and they measure different things. Confuse them and you can badly misjudge how much house you can afford — or misdiagnose why a lender said no.

This guide lays out the difference plainly, works both ratios through a real example, and shows you how to tell which one is the constraint on your own budget.

The two ratios, side by side

Both ratios divide your monthly debt by your gross monthly income. What changes is what counts as “debt.”

• Front-end DTI counts only your housing payment — principal, interest, property taxes, and homeowners insurance (the bundle lenders call PITI), plus any HOA dues. It answers: how much of your income does the house alone consume?
• Back-end DTI counts your housing payment plus every other monthly debt — car loans, student loans, credit-card minimums, personal loans. It answers: how much of your income goes to all your obligations combined?

The two are often quoted together as a pair, like 28/36 — a front-end target of 28% and a back-end target of 36%. Those specific numbers are common guidelines, not universal law; different loan programs use different limits. But the structure is always the same: one ratio for housing alone, one for everything.

The 28/36 rule in one place

The “28/36 rule” is just the two ratios expressed as ceilings:

• Keep the housing payment under 28% of gross monthly income (front-end).
• Keep total debt payments under 36% of gross monthly income (back-end).

It is a durable rule of thumb because it protects against two different failure modes at once. The front-end limit stops you from buying too much house relative to your income. The back-end limit stops your other debts from combining with a reasonable house payment into a total that strains the budget. You need to clear both.

Worked through: the same buyer, both ratios

Let these be illustrative numbers, not current figures. Say you earn $8,000 a month gross, and you are considering a home with a $2,000 monthly PITI payment. Separately, you carry $600 a month in car and student-loan payments.

Against a 28/36 target, this buyer clears both: 25% is under 28, and 32.5% is under 36. The loan looks approvable on DTI.

Now change one thing. Suppose the other debts are $1,400 a month instead of $600:

The front-end ratio did not move — the house payment is the same. But the back-end ratio blew past 36%. This buyer might be told they qualify for less house, or need to clear some debt first, even though the home itself is perfectly reasonable for their income. The other debts, not the house, are the problem.

Which ratio actually holds you back

For most buyers, the back-end ratio is the binding constraint — the one that runs out of room first. That is because it carries the extra weight of your existing debts on top of the housing payment. If you have meaningful car or student-loan payments, you will usually hit the back-end ceiling before the front-end one.

The front-end ratio tends to bind only when you carry very little other debt but are reaching for an expensive home relative to your income. In that case the house alone can push past 28% while your back-end stays fine.

Knowing which one is tight tells you what to do:

• Back-end is the limit? Paying down other debts is the fastest way to raise your budget. Every dollar of monthly debt you clear frees a dollar for housing. This is the more common situation — and the reason DTI, not income, tends to cap your budget.
• Front-end is the limit? The issue is the house itself relative to your income. A larger down payment or a less expensive home is the lever.

Why this matters before you shop

Understanding the two ratios changes how you read an affordability estimate. If a calculator or a lender tells you a maximum, the useful follow-up is: which ratio produced that number? If it was the back-end, some of your budget is being consumed by debts you could pay off. If it was the front-end, you are simply near the top of what your income supports for housing alone.

The Home Affordability Calculator reports both your front-end and back-end DTI right alongside your maximum home price, so you can see which one is doing the limiting. Adjust your debts and watch the back-end ratio move; adjust the home price and watch the front-end ratio move. To see how those ratios translate into an actual budget, start with how much house can I afford on my income. And if you are still weighing whether to buy at all, the Rent vs. Buy Calculator compares owning against renting over time.

Frequently asked questions

What is the difference between front-end and back-end DTI?

Front-end DTI counts only your housing payment — principal, interest, taxes, and insurance — against your gross monthly income. Back-end DTI adds every other monthly debt, such as car loans, student loans, and credit-card minimums, on top of the housing payment. Lenders usually weigh back-end DTI most heavily because it reflects your total obligations.

What is the 28/36 rule?

The 28/36 rule is a common affordability guideline: keep your housing payment under about 28% of gross monthly income (front-end DTI) and your total debt payments under about 36% (back-end DTI). Both ceilings should be met. The exact percentages vary by loan program, but the two-ratio structure is standard.

Which DTI matters more, front-end or back-end?

Lenders generally weigh back-end DTI most heavily because it captures all your debt, not just housing. For most buyers the back-end ratio is also the one that runs out of room first, since it carries existing car and student-loan payments on top of the mortgage. The front-end ratio tends to bind only when you carry little other debt but are reaching for an expensive home.

Not financial advice. The figures above are illustrative examples, not current lending limits. Actual DTI targets vary by loan program, credit, and lender. Confirm real numbers with a licensed lender before deciding.