What debt-to-income measures and why lenders lead with it
Debt-to-income compares the payments you are committed to with the income you have to make them from. It is deliberately crude: it ignores your assets, your spending habits and how much of the payment is principal you get back. What it captures is the one thing that predicts default better than almost anything else — how little room is left in the month when the bills arrive.
Underwriters read two versions. The front-end ratio is the housing payment alone over gross monthly income, and it answers whether the house itself is affordable. The back-end ratio adds every other recurring obligation on your credit report and answers whether you can carry the house alongside everything else. The back-end ratio is the binding one in almost every file; the front-end matters most when a large payment is being taken on with very little other debt.
Both use gross income, before tax and before your 401(k) contribution. That surprises borrowers who budget from net pay, and it is why a 43% back-end ratio can feel like far more than 43% of the money that reaches your account. If you want the net-pay view alongside it, run your gross figure through the take-home pay calculator and divide your obligations by that instead — the result will be roughly a quarter higher, and it is the number your budget actually lives on.
What goes in the numerator, and what does not
The rule underwriters apply is simple: if it appears on your credit report as a recurring monthly payment, it counts. That means mortgages, rent when you are keeping it, auto loans and leases, student loans, credit card minimums, personal loans, 401(k) loans that report, and court-ordered alimony or child support. A co-signed loan counts against you unless you can document twelve months of someone else paying it.
What does not count is anything that is not a debt payment: utilities, phone bills, groceries, insurance premiums that are not part of the escrow, taxes, childcare, and 401(k) contributions. Nor does the balance of a debt — only its monthly payment. A $30,000 card balance with a $600 minimum hurts your ratio four times as much as a $30,000 balance with a $150 minimum, which is exactly why a consolidation loan that stretches the term can improve a DTI without reducing what you owe by a cent.
Two treatments catch people out. Deferred student loans still count: when the credit report shows a zero payment, Fannie Mae and FHA both substitute a calculated figure, commonly 0.5% or 1% of the outstanding balance, so a $60,000 balance in deferment can add $300–$600 to your numerator. And an instalment loan with fewer than ten months left can be excluded under Fannie Mae's rules if the payment is not large enough to affect your ability to pay in the near term, which is a genuine lever when a car loan is nearly finished.
Worked example: $5,000 a month with $2,700 of payments
You earn $60,000 a year, so gross monthly income is 60,000 ÷ 12 = $5,000. You are buying a home with a $1,800 PITI payment, you have a $500 car loan and $400 of card minimums, and your lender wants you at 43%.
- Total the obligations. 1,800 + 500 + 400 = $2,700.
- Front-end ratio. 1,800 ÷ 5,000 = 0.36 = 36.0%. That is above both the 28% conventional guideline and FHA's 31% starting point.
- Back-end ratio. 2,700 ÷ 5,000 = 0.54 = 54.0%, which is above every published limit including Fannie Mae's 50% automated ceiling.
- Payments to remove. At a 43% target you are allowed 0.43 × 5,000 = $2,150 of obligations, so you must remove 2,700 − 2,150 = $550 a month. Clearing the card balances outright removes $400 of it; the remaining $150 has to come from the car loan or a smaller house.
- Or add income. Holding the payments at $2,700, you need 2,700 ÷ 0.43 = $6,279.07 of gross monthly income — a raise of $1,279.07 a month, or $15,348.84 a year.
- Note the exchange rate. $1,279.07 of income does the work of $550 of payments, and 1,279.07 ÷ 550 = 2.326 = 1 ÷ 0.43. That is exact, not a coincidence: the income you need is the payment reduction divided by the target ratio, so at a 43% target every dollar of monthly payment you kill is worth $2.33 of gross monthly income.
Cutting debt is therefore the cheaper lever by a factor of 1/t — and the only one you fully control.
What counts as a good ratio
Below 36% back-end you are inside the most conservative common guideline and no program will decline you on the ratio alone. Between 36% and 43% you are in the range every agency program lends in routinely, and the file turns on your credit score, reserves and down payment rather than the ratio. Between 43% and 50% you need an automated approval and something in support — months of reserves, a large down payment, a high score, or residual income on a VA loan. Above 50% conventional financing is closed to you and the realistic options are FHA with strong compensating factors, or buying less house.
The 43% figure has a specific history worth knowing. The Consumer Financial Protection Bureau's 2013 ability-to-repay rule made 43% the hard ceiling for a General Qualified Mortgage, using the income and debt calculations of Appendix Q. The Bureau replaced that in its 2020 General QM Final Rule with a price-based test tied to the loan's APR relative to the average prime offer rate, with mandatory compliance from 1 October 2022. The 43% line survives anyway, because lenders kept it as an internal screen and because borrowers learned it. Treat it as an underwriting convention, not a legal limit.
The front-end ratio deserves its own look even when the back-end passes. A 28% housing ratio with almost no other debt is a much safer position than a 20% housing ratio propped up beneath 16% of car and card payments, because rent and mortgage payments are the hardest line in a budget to cut quickly. If your front-end ratio is the one that fails, the fix is price, term or down payment — test the combinations with the mortgage payment calculator.
Published DTI limits by loan program
| Program | Front-end | Back-end | Where it comes from |
|---|---|---|---|
| Conventional rule of thumb | 28% | 36% | The long-standing 28/36 guideline lenders quote to borrowers |
| Fannie Mae, manual underwriting | — | 36%, up to 45% | Selling Guide B3-6-02; above 36% requires credit score and reserve minimums |
| Fannie Mae, Desktop Underwriter | — | 50% ceiling | Selling Guide B3-6-02 maximum allowable DTI |
| FHA | 31% | 43% | HUD Handbook 4000.1; higher with compensating factors |
| VA | — | 41% | VA Lenders Handbook M26-7; exceeded when residual income clears the regional table by 20% |
| USDA Guaranteed | 29% | 41% | USDA Handbook HB-1-3555; waivers available through the automated system |
A ratio inside these numbers is a screening pass, not an approval. Credit, reserves, appraisal and employment all still apply.
Mistakes that produce the wrong ratio
- Using net pay. Every published limit is expressed against gross income. Using take-home pay overstates your ratio by roughly a quarter and can make an approvable file look hopeless.
- Entering your current rent as well as the new mortgage. Only the housing payment you will actually have counts. If you are keeping the old home as a rental, different rules apply and the lender will offset the payment with a portion of the documented rent.
- Using what you pay on cards rather than the minimum. Underwriters use the minimum shown on the credit report. Paying $800 against a $160 minimum helps your finances and does nothing to your DTI.
- Leaving out deferred or income-driven student loans. A $0 payment on an income-driven plan is not always accepted; agency rules substitute a percentage of the balance in several situations. Check the treatment with your loan officer and model the payment with the student loan payment calculator.
- Counting bonus or overtime income you cannot document. Variable income generally needs a two-year history and is averaged, not annualised from the best year.
- Forgetting that the housing payment includes escrow. Property tax, hazard insurance, HOA dues and mortgage insurance all sit inside the front-end numerator, and together they routinely add 25–40% on top of principal and interest.
Moving the ratio before you apply
Three levers work, in descending order of speed. Retire small instalment loans outright — a $450 car payment removed is worth $450 of numerator immediately, and under Fannie Mae's rules a loan with fewer than ten payments left may be excluded without paying it off at all. Move card balances to a longer instalment loan, which lowers the required monthly payment even though the debt is unchanged; the consolidation calculator shows what the new payment would be, and the snowball calculator shows how fast the balances disappear if you would rather kill them. Add documented income, which is the slowest lever because most lenders want a two-year history of anything variable.
What does not work is a larger down payment on its own. It lowers the loan and therefore the payment, so it moves both ratios, but the effect is proportional to the principal and interest share of your PITI only — tax, insurance and HOA are unchanged. And paying down a credit card without closing it improves your credit utilisation and your score long before it changes your DTI, because the minimum payment falls slowly.