Debt-to-Income Ratio Calculator
Result
Back-end ratio
- Front-end ratio
- 25.7%
- Total monthly debt
- 2,450.00
- Room left under 36%
- 70.00
- Room left under 45%
- 700.00
- Room left under 50%
- 1,050.00
The arithmetic on this page is three divisions, and you could do all three on paper. What you cannot do on paper is know where the lines are — so that is what the page is for. Two ratios get used. The front-end ratio is the housing payment divided by gross monthly income: 1,800 of housing against 7,000 of income is 25.7%. The back-end ratio divides everything by the same income, including the car payment, the student loan, the minimums on the cards and any child support: add 650 of those and the back-end ratio is 35%. Both are shown because lenders quote both, and because they answer different questions — the first is whether the housing payment itself is affordable, the second is whether the whole set of obligations is. Then there are the thresholds, and this is the part worth reading carefully. On a 7,000 income the three lines sit at 2,520, 3,150 and 3,500 of total monthly debt, so the current 2,450 leaves 70 of room before the first one, 700 before the second and 1,050 before the third. Those three numbers come from one institution's underwriting guide, not from a statute, and they are not even the same line for the same borrower — the lowest applies when a loan is underwritten by hand, the middle one applies to a hand-underwritten loan that meets extra credit score and reserve requirements, and the highest applies to loans run through the automated underwriting system. Different programs, different lenders and different loan types move them again. What the page says is not whether a lender will approve you, because that also depends on your credit score, your reserves and your down payment. What it says is how far you are from the reference points everyone argues about, in the units the argument uses. The pair is quoted together as DTI, and it does more to decide mortgage qualification than any other single figure you can put on an application. One detail trips up more people than any other: the denominator is gross income, before tax, and using take-home pay instead pushes every ratio up by roughly a third. If your numbers look worse than you expected, check that first.
7,000 of gross monthly income, and the three thresholds applied to it
| Threshold (%) | Max total debt | Headroom |
|---|---|---|
| 36 | 2520 | 70 |
| 45 | 3150 | 700 |
| 50 | 3500 | 1050 |
Current total monthly obligations are 2,450, so the third column is what is left of each line. Read it as three different answers to the same question, because that is what it is: 70 of room against the 36% line means one more monthly obligation of any size at all puts you past it, while 1,050 against the 50% line is a real margin. The thresholds are not tiers of one scale that you climb — they belong to different ways of underwriting the same loan, so which line applies to you depends on how the loan is assessed rather than on how much you earn. That is why this table has three rows instead of one, and why the page does not tell you whether you qualify.
Formula
Front-end ratio = housing payment ÷ gross monthly income. Back-end ratio = (housing payment + other monthly debt payments + the payment on any debt being applied for) ÷ gross monthly income. Headroom at each threshold = (threshold × gross monthly income) − total monthly debt obligations.
- I
- Gross monthly income, before tax
- H
- Housing payment: rent or the current mortgage payment
- D
- Other monthly debt payments: instalment loans, student loans, card minimums, child support
- P
- The payment on a debt being applied for, which only enters the back-end ratio
- R
- Back-end ratio: total monthly obligations divided by gross monthly income
- G
- Headroom at a given threshold, in the same unit as the income
Use it before applying, and again after any change that moves the numbers, because both the ratio and the room around it are things you can alter on purpose. Three moves lower the back-end ratio and they are not equally easy: paying down an instalment debt removes its payment from the numerator entirely, which is the largest single effect available; earning more moves the denominator; and taking on a new payment moves the numerator the wrong way. The headroom figures are the practical output — 70 of room against the lowest line is a warning, because a single new monthly obligation of any size puts you over it, while 1,050 against the highest one is the room that actually matters if the loan is going through automated underwriting. The page is also useful in the negative direction, for deciding whether to take on a debt: a 400 a month car payment on a 7,000 income moves the ratio from 35% to 40.7% and turns the 70 of headroom into a 330 shortfall. None of this says whether you will be approved, and none of it is your lender's actual model — your lender's model is the one that counts.
Worked examples
7,000 of income, 1,800 of housing and 650 of other debt
- Total monthly obligations: 1,800 + 650 = 2,450
- Front-end ratio: 1,800 ÷ 7,000 = 25.7%
- Back-end ratio: 2,450 ÷ 7,000 = 35%
- The lowest threshold applied to 7,000 is 36%, which is 2,520 of debt
- Headroom against it: 2,520 − 2,450 = 70
- The other two thresholds are 45% and 50%, which are 3,150 and 3,500, leaving 700 and 1,050
The default case, and the one that shows why two ratios are printed rather than one: the housing payment looks comfortable at 25.7%, and the full set of obligations is close to the lowest threshold at 35%. Both readings are correct and they are about different things. The number to sit with is the 70 of headroom — on this income, one more monthly obligation of any size at all puts the back-end ratio above the lowest line, and the middle and upper lines are a long way off.
The same household taking on a 400 a month payment
- The proposed payment enters the back-end ratio and nothing else
- Total monthly obligations: 1,800 + 650 + 400 = 2,850
- Front-end ratio is unchanged at 25.7%, because the housing payment did not change
- Back-end ratio: 2,850 ÷ 7,000 = 40.7%
- Headroom against the 36% line: 2,520 − 2,850 = −330, so that line is passed
- Headroom against the 45% and 50% lines: 300 and 650
Two things happen here and only one of them is obvious. The first is that the back-end ratio moves from 35% to 40.7% while the front-end ratio does not move at all — which is the entire reason the two are reported separately, since the housing payment is untouched by a car loan. The second is the sign on the first headroom figure: −330 is not an error and it is not zero, it says the lowest line is already behind you. A loan approved by hand without the extra credit score and reserve requirements would fail at that point; the same loan run through automated underwriting has 650 of room left. Same household, same debts, two different answers, because the lines are not one line.
2,400 of housing on 6,000 of income, with no other debts
- Total monthly obligations: 2,400, which is all housing
- Front-end ratio: 2,400 ÷ 6,000 = 40%
- Back-end ratio: the same 2,400, so also 40%
- The two ratios are equal whenever there is no other debt
- Headroom against the 36% line: 2,160 − 2,400 = −240
- Headroom against the 45% and 50% lines: 300 and 600
The case that separates the two ratios by making them identical. With no other debt the back-end ratio is the front-end ratio, which is worth seeing once: it shows that the second ratio is not a different measurement, it is the same one with more added to the numerator. It also isolates how much a housing payment alone can consume. 40% of gross income going to housing clears the lowest line and sits comfortably inside the upper two — on this income the constraint is the housing payment itself, and no amount of paying down other debts changes it by a single point.
Limitations
The three thresholds on this page come from one institution's underwriting guide, and that institution is Fannie Mae, a government-sponsored enterprise in the United States that sets the rules for the mortgages it buys. They are not a legal limit anywhere, they are not the only thresholds in use, and they are not the thresholds your lender applies: the automated underwriting system has its own, government-backed loan programmes such as FHA, VA and USDA have their own, and portfolio lenders who keep loans on their own books have their own again. Treat them as reference points rather than rules. Nothing here says whether you would be approved, because approval also depends on credit score, cash reserves, down payment, property type and the lender's own risk appetite, none of which appear in a ratio. The housing payment field takes one number, and the situation where a new mortgage replaces rent rather than being added to it is the one that field cannot express — enter the housing payment you would have, not both. Other debt payments are counted only where they are genuinely debts: rent, utilities, phone bills and insurance are not, and putting them in the numerator inflates the ratio. Child support and alimony are treated as debt here, while a lender may deduct them from income instead, which produces a different answer on the same facts. The proposed payment field covers one new obligation, so several at once have to be added up by hand. And the denominator is gross income, before tax — the single most common way these ratios come out too high is someone entering take-home pay.
Frequently asked questions
- What is a good debt-to-income ratio?
- There is no single answer, because the lines are set by lenders and programmes rather than by law. The reference points this page uses are 36%, 45% and 50% of gross monthly income for total monthly obligations, and they come from one institution's underwriting guide. A ratio below the lowest of them is the safest position; above the highest, an automated approval becomes unlikely.
- What is the difference between the front-end and the back-end ratio?
- The front-end ratio is housing divided by income, and the back-end ratio is everything divided by income. On 7,000 of income with 1,800 of housing and 650 of other debt they are 25.7% and 35%. The reason both are reported is that a new car loan moves the second one and not the first, which is exactly the distinction a lender is drawing.
- Why is there no 43% threshold here?
- Because it could not be sourced. The widely-quoted 43% figure does not appear in the ability-to-repay rule, and a threshold that cannot be traced to the body that issued it is not put on a page. The three lines shown are quoted word for word from the underwriting guide cited below, along with the conditions that apply to each.
- Should I use gross income or take-home pay?
- Gross income, before tax, because that is what lenders divide by. Using take-home pay makes every ratio on this page roughly a third higher than the number a lender would calculate from the same debts, which is the most common reason a household's own estimate comes out worse than the one they are quoted.
- Does paying off a credit card help my ratio?
- It helps by removing the monthly payment from the numerator, not by reducing the balance. Clearing an instalment loan removes its whole payment, which is the largest single effect available; clearing a card removes only the minimum that was being counted, which is much smaller. Closing the account changes nothing by itself.
- Is a negative headroom an error?
- No — it means that threshold is already passed. The second example has headroom of −330 against the lowest line and 300 against the middle one. A negative figure is not a forecast of rejection either: the same household may sit comfortably inside a different programme's limits, because the lines are not one line.
References
- Selling Guide B3-6-02, Debt-to-Income Ratios: the underwriting guide that states the 36%, 45% and 50% thresholds quoted on this page, and the conditions attached to each — Fannie Mae Selling Guide, Fannie Mae (United States)
- 12 CFR 1026.43(c)(7) — Minimum standards for transactions secured by a dwelling (Regulation Z): defines total monthly debt obligations, and requires a creditor that considers the ratio to consider it — without setting any maximum anywhere — Electronic Code of Federal Regulations, Office of the Federal Register (United States)