How this DTI calculator works
Before a lender decides how much to lend you, it asks a blunt question: how much of your income is already spoken for? The debt-to-income ratio (DTI) is the answer. It divides your recurring monthly debt payments by your gross monthly income, and it is one of the two or three numbers that decide whether a mortgage application is approved and at what rate.
At a glance
- Front-end DTI counts housing only; back-end adds every other debt payment.
- Lenders compare the back-end ratio with 36%, 43% and, in some cases, 50% limits.
- Only recurring debt payments count, not groceries, utilities or childcare.
- Clearing a small loan entirely can lower DTI more than paying down a large one.
This calculator works out both versions lenders use. The front-end ratio looks only at housing. The back-end ratio adds every other debt payment, and it is the one that matters most. It then compares your figures with the limits used for conventional, FHA and qualified-mortgage lending, and tells you the largest housing payment and total debt load the common 28/36 guideline would allow on your income.
The formulas
Front-end DTI = Housing costs ÷ Gross monthly income
Back-end DTI = (Housing costs + Other debt payments) ÷ Gross monthly income
Turned round, the same formulas give the payment a lender would accept:
Max housing payment = Gross monthly income × 28%
Max total debt = Gross monthly income × 36%
Worked example: the default figures
Gross income $8,000 a month. Housing $2,000. Car $400, student loan $250, credit-card minimums $150.
Front-end: 2,000 ÷ 8,000 = 25%. Back-end: (2,000 + 800) ÷ 8,000 = 2,800 ÷ 8,000 = 35%.
Both sit inside the 28/36 guideline. The maximum housing payment at 28% is $2,240, and total debt at 36% is $2,880, leaving just $80 a month of headroom before the back-end limit.
Worked example: a bigger house payment
Same income and debts, but a $2,500 housing payment.
Front-end: 2,500 ÷ 8,000 = 31.25%. Back-end: 3,300 ÷ 8,000 = 41.25%.
The back-end ratio is still under 43%, so a qualified mortgage is possible, but the front-end figure now exceeds both the conventional 28% and the FHA 31% guidelines. A lender may still approve with strong credit and savings, or may ask for a larger down payment to bring the payment down.
What counts as debt
Lenders count payments that recur and appear on a credit report:
- Mortgage or rent, plus property tax, homeowner's insurance and HOA or condo fees
- Car loans and leases
- Student loans (usually the actual payment; some programmes use a percentage of the balance if the loan is deferred)
- Personal loans and buy-now-pay-later instalments
- Credit card minimum payments, not the balance and not what you usually pay
- Court-ordered child support or alimony
Everyday spending, groceries, utilities, phone, car insurance, subscriptions, childcare, is not debt for DTI purposes, however real it feels in your budget. That is why a DTI that passes a lender's test can still leave you stretched; the ratio measures borrowing capacity, not comfort.
Reading the bands
| Back-end DTI | What it usually means |
|---|---|
| Under 36% | Comfortable. Most lenders and loan types available; best pricing. |
| 36% to 43% | Acceptable for many conventional and FHA loans, often with a good credit score or cash reserves. |
| 43% to 50% | Possible with strong compensating factors; fewer lenders, tighter terms. |
| Over 50% | Most lenders decline. Reduce debt or increase documented income first. |
The thresholds shown are widely used US guidelines rather than legal ceilings. Automated underwriting systems approve conventional loans up to 50% in some cases, and the 43% figure comes from the US qualified-mortgage rule, where it now serves as a benchmark rather than a hard cap. Lenders in other countries use similar arithmetic with different limits, UK lenders, for instance, tend to think in loan-to-income multiples and affordability stress tests rather than a DTI percentage.
Lowering your ratio
Two levers move the number: less debt or more income. On the debt side, clearing a loan or card entirely removes its full payment from the calculation, which is why paying off a $3,000 car loan with a $300 payment can help more than paying $3,000 off a mortgage. Avoid opening new credit in the months before an application. On the income side, make sure everything documentable is included, a second job with a two-year history, regular bonuses, rental income, because lenders can only count what you can prove.
What this calculator does not do
It does not check your credit score, loan-to-value ratio, cash reserves or employment history, all of which sit alongside DTI in a lending decision. It also uses the simple monthly-payment definition; a lender may treat deferred student loans, co-signed debts or debts with under ten payments remaining differently.
Using the result
Treat the back-end ratio as your borrowing thermostat. Under 36% you can shop widely and negotiate; between 36% and 43% focus on lenders that suit your credit profile and consider trimming a debt before applying; above 43% the most productive step is usually to pay off the smallest loan in full. And whatever the ratio says, run the mortgage payment through your real monthly budget, the one that includes groceries, before you commit.