Debt-to-Income Calculator
Compute the two ratios mortgage underwriters check first: front-end DTI (housing ÷ gross income) and back-end DTI (housing + all debts ÷ gross income), read against the standard 36% / 43% guideline bands.
Your DTI ratios
Example: $10,000/mo income, $2,500 housing, $800 debts → 33% back-end.
Companion guide: How affordability is estimated follows the same two ratios in the other direction — from income and debts to a housing budget and a maximum home price — on a fictional household. This page covers the ratios themselves: how the engine computes and labels them, and what the label does not mean. Every explainer on the site is listed under Guides.
What the two ratios measure
A debt-to-income ratio is the share of gross monthly income claimed by fixed monthly payments, and the calculator reports two. The front-end ratio counts the housing payment alone: housing ÷ gross monthly income. The back-end ratio adds every other recurring debt payment: (housing + other debts) ÷ gross monthly income. In the worked example — a fictional household with $10,000 of gross monthly income, $2,500 of housing and $800 of other monthly payments — the front-end ratio is 25%, the back-end ratio is 33%, and the engine labels the back-end figure comfortable. The two differ by 8 points, the share of income the other payments take, because the housing term is the same in both. Every figure on this page is computed at build time by the same tested engine that powers the form, and every dollar amount is a fictional input chosen for the arithmetic.
What the engine computes, step by step
The form hands your three entries to one engine function; the interface only formats what comes back and never does arithmetic of its own.
- Validation. Income must be a finite number greater than zero; the housing payment and the other debts may be zero but not negative; each figure has an upper bound. A zero income is refused before any division runs, with the engine's own message: "The monthly income must be greater than 0."
- Front-end ratio = housing ÷ income × 100: $2,500 ÷ $10,000 × 100 = 25%.
- Back-end ratio = (housing + other debts) ÷ income × 100: ($2,500 + $800) ÷ $10,000 × 100 = 33%.
- Label. The back-end ratio is compared with three fixed boundaries and given one of four labels; the front-end ratio takes no part in it.
| Line | How the engine computes it | Result |
|---|---|---|
| Front-end ratio | $2,500 ÷ $10,000 × 100 | 25% |
| Back-end ratio | ($2,500 + $800) ÷ $10,000 × 100 | 33% |
| Label | Back-end ratio against the engine's boundaries | comfortable |
Reading the bands
The label is a reading of the back-end ratio and nothing more — the engine's own header calls it a conventional-guideline reading. Its boundaries are fixed inside the engine, so this page reads them back rather than typing them: when the page is built, a fictional $10,000 income is run through the engine one dollar of housing at a time and the ratio at which each label last applies is recorded. A back-end ratio at or below 36% is labelled comfortable; above that and at or below 43%, at the limit; above that and at or below 50%, stretched; above 50%, over the line.
Each boundary is inclusive, and the comparison is made on the unrounded value. On the probe income, housing of $3,600 with no other debts gives 36% and the label comfortable; one dollar more, $3,601, gives 36.01% and at the limit. The label is a step, not a grade.
What the label is not is a decision. The methodology page states the limit: "Affordability reflects general lender guidelines, not an underwriting decision. Actual approval depends on credit, employment history, the loan program, and lender-specific overlays."
What moves each ratio
The three inputs act differently. The debts field touches the back-end ratio only: on the example income, $900 of other payments instead of $800 moves it from 33% to 34% — a rise of 1%, which is the share of the income the added $100 represents — and leaves the front-end ratio at 25%. Raise the other payments to $1,800 and the back-end ratio reaches 43%, labelled at the limit: it sits exactly on a boundary, and the boundary is inclusive. The housing field moves both ratios by the same amount, since it appears in both numerators. The income field moves both as a divisor.
The income figure: gross, and monthly
The field asks for gross monthly income — before taxes and deductions — because that is the convention the ratios are defined on, and the engine divides by whatever is entered. Enter annual income and every ratio shrinks twelvefold: the example household's $120,000 a year typed into the monthly field returns 2.08% and 2.75%, labelled comfortable, figures no payment in the example supports. Enter take-home pay and every ratio grows: a fictional $7,500 of net monthly income in place of the $10,000 gross figure lifts the back-end ratio from 33% to 44% and the label from comfortable to stretched, with no change to any payment.
The housing figure: what belongs in the field
The housing field is one monthly amount, and the engine adds nothing to it. The label says what belongs there — rent, or the full mortgage payment with taxes and insurance (PITI) plus HOA dues — but the engine does not compute that total; the Mortgage Calculator does. Example D takes the fictional purchase from that page — a $400,000 home with $80,000 down at 6.5% over 30 years, an illustrative 1.1% property-tax rate and $1,800 a year of insurance — whose monthly total the mortgage engine returns as $2,539.28: $2,022.62 of principal and interest, $366.67 of tax and $150.00 of insurance. Against the example's $10,000 income and $800 of other payments, that total gives a front-end ratio of 25.39% and a back-end ratio of 33.39%, labelled comfortable. Entering the principal-and-interest figure alone understates both ratios by 5.17 points — the share of income the tax and insurance lines take.
The same ratios, run in the other direction
The methodology page states in one sentence where these ratios are used elsewhere on the site: "Affordability uses the 28/36 debt-to-income guidelines, and property tax that scales with the home price is solved with a closed-form rearrangement rather than an approximation." The House Affordability Calculator starts from income and debts and solves for the largest housing payment inside two limits; this calculator starts from a housing payment and reports the ratios it produces. The two engines agree, and this page checks that when it is built. The fictional household in the affordability guide — $90,000 of gross annual income, or $7,500 a month, with $400 of monthly debts — is given a housing budget of $2,100.00, limited by its front-end ratio. Fed back through this calculator with the same income and debts, that budget gives a front-end ratio of 28% — the housing share the affordability engine applied — and a back-end ratio of 33.33%, labelled comfortable. Raise the household's debts to $900 and the budget falls to $1,800.00, limited by its back-end ratio; run through this calculator, the back-end ratio is 36%, exactly on the first boundary, labelled comfortable.
How to read the result
The result box shows four lines, each taken from the engine's output. The headline is the back-end ratio followed by its label — 33% back-end DTI (comfortable) on the example inputs — and it is the only line that carries a label. Front-end (housing only) is housing ÷ income, 25%; Back-end (housing + all debts) repeats the headline ratio without the label; Reference bands is a fixed line listing the four ranges and does not change with your inputs.
Ratios are shown to two decimal places, and the one-line example above the form rounds to one. Internally the engine keeps the full precision of IEEE-754 double-precision arithmetic and decides the label on the unrounded value, so a displayed figure can appear to sit on a boundary while the label says it has crossed it: on the probe income, housing of $3,600.40 gives a ratio the box displays as 36% with the label at the limit, because the unrounded ratio is a few thousandths of a point above the boundary. The displayed value is a rounded view of a more precise internal one — the difference is presentational, not an error. The Copy result button places the two ratios and the label on your clipboard as one line.
Where the calculator stops
The limits are the engine's. It performs two divisions and one comparison; it holds no list of what counts as income or as debt, so whatever is entered is counted in full and whatever is left out is not counted at all. The closing note on this page states the consequence: loan programs define countable income and debts in detail, and lender overlays vary. The engine models nothing about qualification — in the methodology page's words, affordability "reflects general lender guidelines, not an underwriting decision." Inputs are validated before any arithmetic runs; a figure beyond the engine's upper bound, for instance, returns "The monthly income is larger than this tool supports." A correct calculation can still be the wrong calculation for your situation — choosing the right loan for a real-world decision is judgment we cannot automate.
Common misreadings
- Entering annual income. The field is monthly; an annual figure divides every ratio by twelve — the 2.75% example above.
- Entering balances in the debts field. The field is the sum of monthly payments; a balance is not a payment.
- Entering principal and interest alone as housing. The field is the full housing payment, tax and insurance lines included, as Example D shows.
- Reading the label as a decision. It is the position of the back-end ratio against three fixed boundaries, decided on the unrounded value.
Frequently asked questions
What counts as debt in the back-end ratio?
Exactly what is in the two payment fields: the housing payment plus the sum entered as other monthly debt payments — the engine holds no list of its own. The field label names the usual contents of that sum, loan payments and credit-card minimums: recurring obligations rather than everyday spending such as utilities, groceries, subscriptions or insurance premiums. Homeowners insurance is already inside a PITI housing payment, so it is not entered twice. Loan programs define countable income and debts in detail, and lender overlays vary.
Is income gross or take-home?
Gross — before taxes and deductions — which is what the field asks for. The ratios are shares of gross monthly income, which is why they look more forgiving than a take-home budget feels. The engine divides by whatever it is given: replacing the example's $10,000 gross figure with $7,500 of take-home pay lifts the back-end ratio from 33% to 44% and the label from "comfortable" to "stretched", with no change to any payment.
What DTI do I need for a mortgage?
This calculator does not answer that question. It computes two ratios from the figures you enter and labels the back-end figure against fixed boundaries inside the engine. The methodology page states the limit: "Affordability reflects general lender guidelines, not an underwriting decision. Actual approval depends on credit, employment history, the loan program, and lender-specific overlays." A pre-approval is the authoritative answer.
What moves each ratio?
The debts field moves the back-end ratio only: on the fictional $10,000 income, $100 more in other payments moves it from 33% to 34% — the added payment's own share of the income — and the front-end ratio not at all. The housing field moves both ratios equally, because it is in both numerators. The income field moves both as a divisor.
Why does the front-end ratio not change when I edit the debts field?
Because the front-end ratio is housing ÷ income, and the debts field is not part of it. Other payments of $800, $900 and $1,800 on the example give back-end ratios of 33%, 34% and 43% while the front-end ratio stays at 25%.
Why does the label not match the ratio I see on screen?
The ratio is rounded to two decimal places for display, but the label is decided on the unrounded value, and each boundary is inclusive. On a fictional $10,000 income, a housing payment of $3,600.40 gives a ratio the box displays as 36% with the label "at the limit", because the unrounded ratio is a few thousandths of a point above the boundary. The displayed value is a rounded view of a more precise internal one — the difference is presentational, not an error.
What happens if I leave the debts field blank?
The engine reads it as zero, and the two ratios come out equal: 25% front-end and 25% back-end on the example income and housing.
Why do I see an error message instead of ratios?
The engine validates every entry before it divides, and returns its own message rather than a number it cannot stand behind: a zero income gives "The monthly income must be greater than 0." a negative payment gives "The debt payments cannot be negative." and a figure beyond the engine's upper bound gives "The monthly income is larger than this tool supports."
Not financial advice: a general educational estimate. Loan programs define countable income and debts in detail, and lender overlays vary — a pre-approval is the authoritative answer. Values are processed locally in your browser and never transmitted. See the methodology page.