What is my debt-to-income ratio?

Both ratios divide monthly debt service by gross monthly income, which is annual income over twelve. At the example inputs, $100,000 a year is $8,333 a month before tax. The $2,000 housing payment alone is 24.0% of it: the front-end ratio. Adding $500 of other minimums makes $2,500 of total debt service, 30.0% of income: the back-end ratio.

The back-end number is the one underwriting rules on. Fannie Mae's Selling Guide sets its limits on the total ratio only, so the front-end figure here is informational: a clean read on how much of the load is the roof rather than the loans. Income is gross because that is how the guide's arithmetic works; nothing here nets out taxes.

While you rent, the rent is the housing payment. When a lender qualifies you for a mortgage, it swaps the rent out for the proposed full house payment, principal, interest, tax, insurance, and dues, and recomputes the same two fractions.

The limits come from one primary source, Fannie Mae Selling Guide B3-6-02, as of 2025-04-02: a maximum total ratio of 36% for manually underwritten loans, up to 45% with credit score and reserve requirements, and 50% as the Desktop Underwriter maximum. They are ceilings on the back-end ratio, not targets; the guide sets no separate front-end line.

The useful translation is dollars, not points. At the example inputs, $2,500 of debt service on $8,333 of monthly income leaves $500 a month of room under the 36% line, $1,250 under 45%, and $1,667 under 50%. That is the car payment or card minimum you could add before crossing each line, and the calculator recomputes it for your numbers as you type.

Cross the top line and the dollars run the other way. The same income carrying $4,300 of debt service sits at 51.6%, $133 a month past even the 50% line; conventional approval at that ratio is unlikely, and the page says so rather than rounding the verdict off.

The ratio has one numerator and one denominator, so there are exactly two moves. On the numerator, paying off $100 of monthly minimums takes 1.2 points off the back-end ratio at the example income; clearing all $500 of minimums drops it to 24.0% and raises the headroom at the 36% line to $1,000 a month. Paying off a loan entirely removes its minimum; paying it down usually does not, which is why the last payment on a car loan moves the ratio and a big extra payment in the middle does not.

On the denominator, earning $5,000 more a year takes 1.43 points off at the example inputs. Income moves the ratio more slowly than debt at these sizes, but it moves every line's dollar headroom at once: each line is a percentage of income, so a raise widens all three at the same time. The drivers list under the result ranks the three moves for the numbers you entered.

Everything else underwriting looks at. Residual income, what is actually left after the bills, can sink an approval that the ratio alone would pass. Credit score and reserves decide whether the 45% and 50% lines are available at all. Program overlays matter too: FHA and VA run their own ratio rules, and individual lenders overlay stricter ones. The lines here are the conventional Fannie Mae limits and nothing else.

The model uses gross income because that is the underwriting convention the source describes. It also trusts your inputs: a lender verifies income from documents, averages variable pay, and reads minimums off your credit report, which may not match what you type here. The ratio is arithmetic; the approval is a judgment this page does not make.

This calculator is built to be used without a browser. Every input is a query parameter on this page, and the same parameters on the JSON twin return the complete answer as a document.

GET /tools/dti.json?income=150000&housing=2500&debts=400

The response carries inputs after parsing and clamping, result with both ratios as fractions, the band, each lender line with its allowed debt and your dollar headroom or overage, the maximum housing payment at the 36 and 45 lines, and sensitivity tables by debts and by income, drivers ranked by effect with a plain sentence each, assumptions that say for every field whether you supplied it and which source the default came from, sources with URLs and as-of dates, warnings, a disclaimer, and in tool the canonicalUrl and jsonUrl that carry only your non-default parameters. The canonical URL is the answer's permanent address; use it when you cite the number.

Parameters, all optional, in any order:

• income ($ per year), default $100,000 per year.
• housing ($ per month), default $2,000 per month.
• debts ($ per month), default $500 per month.

Values accept plain numbers and loose human formats such as 100k, $100,000, or 6.5%. Unknown parameters are ignored, values outside a field's range are clamped and reported in warnings, and the endpoint never fails on bad input. Responses are cacheable for a day; the defaults change when their sources publish, and tool.version changes when the method does.

• Fannie Mae Selling Guide B3-6-02, Debt-to-Income Ratios, as of 2025-04-02. Manually underwritten loans: maximum total DTI 36%, up to 45% with credit score and reserve requirements. Desktop Underwriter: maximum 50%.

The three lines (36, 45, 50) are the only sourced figures on this page. The income, housing, and debt defaults are examples to be replaced, not statistics.

Carlo is a personal finance agent. It knows your accounts, debts, and goals, so instead of a ratio on example numbers it can compute your actual debt-to-income from the accounts you link, watch it as balances change, and tell you what paying off one specific card would do to it. Text it the question.

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