Debt-to-Income Ratio Calculator

The single number most mortgage lenders care about

When a lender decides whether to approve a mortgage, two checks usually run in parallel: affordability (can the income cover the new payments?) and debt-service ratio (is the borrower already over-leveraged?). Debt-to-income ratio is the primary expression of both. Commonly cited orientation ranges treat DTI above 40% as the level where many lenders become cautious and above 50% as the level where approvals become rare. The calculator above produces the ratio; this commentary is about what to do with the number.

Two DTI ratios, not one

Most sources conflate two different ratios. The distinction matters:

Front-end ratio (housing DTI): monthly housing costs (mortgage, local property tax, insurance, maintenance reserve) divided by gross monthly income. Commonly cited orientation ranges put under 28% as healthy, 28–35% as stretched, and above 35% as pressured.

Back-end ratio (total DTI): all debt payments (housing + car loans + credit card minimums + student loans + personal loans) divided by gross monthly income. Commonly cited orientation ranges put under 36% as healthy, 36–43% as stretched, above 43% as pressured, and above 50% as the level where mainstream lending becomes difficult.

Lenders typically use back-end ratio for approval decisions. Budget planners often track both — a low back-end but high front-end signals over-housed; low front-end with high back-end signals other debt problems.

The 28/36 rule and its history

The 28/36 guideline (28% housing, 36% total debt) traces back to mortgage-industry standards that took shape in the 1980s and 1990s. It is not written into regulation, but many lenders apply similar logic internally. Below 28/36, applications tend to be approved at advertised rates. Between 28/36 and 43/50, applications tend to be approved at higher rates with more scrutiny. Above 43/50, non-mainstream lenders and higher rates dominate. The rule is the industry's aggregate judgment about what ratios remain sustainable through realistic income shocks. It is a heuristic, not a guarantee, and specific cutoffs vary by country and lender.

Gross income or net income?

DTI is conventionally calculated on gross (pre-tax) income for a specific reason: lenders compare against gross because tax positions vary while gross is standardised. For personal budget planning, this is partly misleading — the actual capacity to service debt depends on net income after tax. Running the ratio both ways gives a more complete picture. A household at 35% DTI on gross often sits in the mid-to-high 40s on net, especially for upper-rate taxpayers. The gross figure is what lenders see; the net figure is what bank statements feel like.

What counts as "debt" in the calculation

Typically included: mortgage payments, second-mortgage or home-equity-loan (HELOC) payments, auto loan payments, minimum credit card payments, personal loan payments, student loan payments, court-ordered obligations (alimony, child support), and other regular debt service. Typically excluded: rent (if not buying, though some lenders count rent), utilities, insurance (unless bundled with housing), subscriptions, and one-off expenses. Business debts in a self-employed context are usually treated separately by the lender. A common heuristic when in doubt is to err toward over-including rather than under-including, since understated DTI tends to surface during underwriting and can damage the application.

The "committed vs discretionary" extension

A refinement some financial planners use distinguishes committed debt (mortgage, car loan on a necessary vehicle) from discretionary debt (credit card balances from lifestyle spending, consumer loans for non-essentials). The total DTI can be identical, but the portfolios are differently vulnerable. Committed debt is harder to eliminate but typically cheaper. Discretionary debt is more expensive but can be structurally reduced. Two households both at 40% DTI can have very different paths out of it: one needs time; the other needs to restructure spending.

DTI and credit availability

Lenders look at both DTI and credit utilisation (the percentage of available credit being used). These interact. Someone at 35% DTI using 90% of available credit presents a riskier profile than someone at 40% DTI using 30% of credit, because the first is close to the limit of their access to credit and has less room for surprises. The standard guideline of keeping credit utilisation below 30% exists because it changes how lenders read the same DTI figure. Paying down a credit card before a mortgage application can have a dual effect: it lowers DTI and credit utilisation at the same time.

Mortgage affordability beyond DTI

Mortgage lenders typically run something more granular than DTI alone — a detailed income-and-outgoings assessment that includes fixed commitments, childcare, and discretionary-spending estimates. The DTI figure is a summary; the underlying affordability model is what actually drives the decision. Commonly cited mortgage affordability heuristics use 4–4.5× gross income as a loan cap, stress-tested at rates a few percentage points higher than the current fixed rate. The DTI at current rates is therefore less interesting to the lender than the stressed DTI at the reset rate. Some borrowers self-test against a higher rate as a rough proxy for this check; specific stress percentages vary by jurisdiction, lender, and product type.

Improving DTI: the three levers

Three honest approaches can shift DTI:

Pay down debt. Often slow but most effective on high-interest debt with high minimum payments. As a rough orientation, clearing a credit card balance close to one month's gross income commonly moves DTI by 1–3 percentage points, depending on the starting income and balance.

Increase income. Promotion, job change, second income source, negotiated pay rise. Meaningful pay rises can move DTI by several percentage points, again depending on starting income.

Consolidate to longer terms. Extending a 3-year car loan to 5 years reduces the monthly payment and therefore DTI, though it raises total interest paid. This approach is sometimes used in the run-up to a mortgage application where DTI is the binding constraint; it is less suited as a general debt strategy because it tends to raise lifetime interest paid.

What the calculator shows

The tool computes back-end DTI from the income and debt-payment figures provided. It does not automatically separate front-end vs back-end, or distinguish committed from discretionary. Use the number as the starting diagnostic; layer the commentary above for interpretation and planning.