Debt-to-income ratio explained: the number lenders look at

A debt-to-income ratio, usually shortened to DTI, is one of the first numbers a lender works out when someone applies for a mortgage, a car loan or a personal loan. It compares the money going out to creditors each month with the money coming in. This guide sets out exactly what goes into the ratio, works through one household's figures step by step, explains the thresholds that get quoted and where they come from, and shows how paying a debt down or consolidating it changes the result.

What the ratio measures

The definition is a single division:

DTI = total monthly debt payments ÷ gross monthly income

The result is expressed as a percentage. If a household pays 1,900 a month towards its debts and earns 4,500 a month before tax, its ratio is 1,900 ÷ 4,500 = 0.4222, or 42.2%. The US Consumer Financial Protection Bureau describes the ratio in the same terms: all monthly debt payments divided by gross monthly income, used by lenders as one way to measure an applicant's ability to manage the payments on a new loan.

Two things stand out about this definition. It uses payments, not balances, so a large debt with a small monthly payment weighs less than a small debt with a large one. And it uses gross income, so the percentage is lower than most people expect when they first compare their payments with what actually lands in their account.

Front-end vs back-end DTI

Mortgage lenders often split the ratio in two.

• Front-end ratio. Housing costs only, divided by gross income. For a homeowner that is the mortgage payment, usually with property taxes, buildings insurance and any homeowners' association or service charge added. For a renter, it is the rent. In the example above, 1,200 of the 1,900 is a mortgage payment, so the front-end ratio is 1,200 ÷ 4,500 = 26.7%.
• Back-end ratio. Every recurring debt payment, housing included, divided by gross income. This is the 42.2% figure, and when someone says "DTI" without qualification they almost always mean the back-end ratio.

When a lender is assessing a new mortgage, the housing payment used in both ratios is the proposed one, not the current one. A renter paying 900 a month who applies for a mortgage with a 1,200 payment is assessed on the 1,200.

What counts as debt and what counts as income

The ratio only works if the two sides are built consistently. The usual rules are:

The dividing line is whether the outgoing is a contractual obligation to a creditor. A card balance creates one because the issuer requires a minimum payment every month; a grocery bill does not, because there is no balance carried and no creditor. Note that for cards it is the minimum payment that counts, even if the cardholder habitually pays more. Our guide to credit card minimum payments explains how issuers set that figure.

Income means regular, verifiable gross income: salary before tax and deductions, plus any reliable extras a lender will accept, such as consistent overtime, bonuses with a track record, pension income, or rental income net of costs. Irregular or unverifiable money is normally excluded. In the United States, the gross figure is used because it is the one shown on pay documentation and tax returns and it does not depend on each applicant's individual deductions, which makes ratios comparable across applicants. Net pay varies with tax code, pension contributions and benefits, so a ratio built on it would mean something slightly different for every borrower.

Worked example: one household, step by step

Take a household with a gross income of 4,500 a month and four monthly obligations: a mortgage payment of 1,200, a car loan payment of 350, a credit card with a 150 minimum payment, and a student loan payment of 200.

Every variation in this guide uses the same three steps and the same 4,500 of income. The only thing that changes is the total on the top line.

For contrast, the same payments against a net income of 3,500 would give 1,900 ÷ 3,500 = 54.3%. The debts have not changed; only the denominator has. That is why a ratio is only meaningful alongside the definition of income it was built on.

Thresholds lenders quote, and where they come from

The number most often quoted is 43%. It comes from the US Qualified Mortgage rule under Regulation Z, which from 2014 gave lenders legal protection on loans where, among other conditions, the borrower's back-end DTI did not exceed 43%. Until the rule changed, the CFPB's consumer explainer described 43% as the highest ratio a borrower could generally have and still get a Qualified Mortgage. In 2021, however, the CFPB replaced the fixed DTI cap in the general Qualified Mortgage definition with a test based on the loan's price relative to a benchmark rate, so 43% is now better described as a historical benchmark that many lenders still use as an internal guideline than as a legal line.

Beyond that single figure, practice varies widely. Some lenders prefer back-end ratios in the mid-30s; some government-backed programmes accept higher ratios when other factors are strong; and personal loan and car finance lenders each apply their own limits, which are rarely published. A front-end ratio of around 28% is a common rule of thumb for housing costs, but it is a convention, not a rule.

How paying down a debt or consolidating changes the ratio

Because the ratio counts payments rather than balances, the two common ways of reducing debt affect it quite differently.

This is the main reason consolidation is sometimes described as a DTI tool: stretching the same balance over a longer term lowers the monthly payment and therefore the ratio, even though the total interest over the loan's life usually rises. The debt consolidation calculator shows both effects side by side, the change in monthly payment and the change in total interest, and our guide to consolidation loans goes into the trade-off in detail.

A change in income works through the bottom line in the same way. A rise to 5,000 a month with the original 1,900 of payments gives 1,900 ÷ 5,000 = 38.0%, almost the same effect as clearing the card.

What the ratio ignores

DTI is deliberately narrow, and it leaves out most of what determines how expensive a debt actually is.

• Interest rates. A 150 minimum on a card at 24% APR and a 150 payment on a loan at 6% APR contribute identically to the ratio. Yet the card balance will cost far more over time: 6,000 at 24% APR repaid at a fixed 150 a month takes 82 months to clear and generates 6,191.34 in interest, more than the original balance.
• Balances. The ratio has no term for the amount owed. A 40,000 car loan with a 350 payment and a 6,000 card with a 150 minimum are represented only by 350 and 150.
• Time remaining. A loan with two payments left and one with ten years left count the same, as long as the monthly amount is the same.
• Everything that is not a debt. Two households with identical ratios can have very different amounts left over once utilities, childcare, transport and food are paid.

Those gaps are why DTI is one input to a lending decision rather than the decision itself. Lenders combine it with credit history, loan-to-value or loan-to-income, savings and, in the UK, a full expenditure assessment.

Calculating your own

Working out the ratio by hand takes a few minutes:

• List every monthly debt payment. Use the contractual amount: the figure on the loan agreement, or the minimum payment on the latest card statement. Include rent or mortgage, car finance, student loans, personal loans, card minimums and any court-ordered support.
• Leave out living costs. Utilities, groceries, phone contracts, subscriptions and insurance other than any cover included in the mortgage payment are not debts for this purpose.
• Find gross monthly income. For a salary, divide the annual gross figure by 12. For weekly pay, multiply by 52 and divide by 12. Include only income that is regular and that a lender could verify.
• Divide and convert. Total payments ÷ gross income, then multiply by 100.

If the debts include cards or loans you plan to clear, the debt payoff calculator shows which month each one disappears under a fixed budget, which is the month its minimum drops out of the ratio. Recalculating the ratio at each of those points gives a timeline of how it will fall.

Limits of the ratio

A debt-to-income ratio is a snapshot of monthly commitments against monthly earnings, and no more than that. It does not say whether a debt is cheap or expensive, how long it will last, or whether the household has room to absorb a rise in costs. It is sensitive to definitions: which payments count, whether income is gross or net, and whether a lender uses the current or the proposed housing payment all shift the result by several points. The thresholds attached to it are conventions that differ between countries, lenders and loan types, and some of the best-known figures, including 43%, are tied to rules that have since changed.

Used with those caveats, the ratio is a quick and useful check. Because it moves in predictable steps, it can be worked out in advance of an application and again after any change in payments or income, with nothing more than addition and a single division.

This guide explains how things work in general terms. It isn’t financial, tax or legal advice. Spotted something out of date? Email errors@debtwren.com and we’ll check it against the source.