How to Calculate Debt-to-Income Ratio

How is debt-to-income ratio calculated?

Your debt-to-income ratio is every monthly debt payment divided by your gross monthly income. The Consumer Financial Protection Bureau defines it in exactly those terms.

Two inputs account for most wrong answers.

Gross, not net. Use income before tax and deductions, not what lands in your account. Someone on $72,000 has $6,000 a month of gross income and perhaps $4,950 of take-home. Using the take-home figure turns a 36% ratio into 44%, and people talk themselves out of applying on the strength of a number the lender was never going to calculate.

The payment, not the balance. A $40,000 student loan on a $210 a month plan contributes $210. The size of the debt behind the payment does not enter the calculation. This is why someone with one large mortgage can look healthier than someone with four small loans, and it is the single most useful thing to understand about the ratio: it measures monthly commitment, not indebtedness.

What counts as a debt payment?

A lender is not measuring your cost of living. It is measuring the fixed obligations that would still arrive if you cut everything else back.

The credit card rule catches careful people out. The lender counts the minimum printed on your statement, not what you actually pay. If you clear your card in full every month, you are still charged a minimum in this calculation, because that is the contractual obligation. It feels unjust to someone who has never carried a balance, and it is simply how the ratio is defined.

One thing that is often missed in the other direction: if the property you are buying has homeowners' association dues, they go into the housing payment. On some condominiums that is $400 a month, which is a serious amount of ratio to discover late.

When your income is not a simple salary

This is where the calculation stops being arithmetic and starts being documentation. A lender does not count income it cannot evidence.

The self-employed case is the one worth planning around, because it has a genuine conflict built into it. Claiming every legitimate expense reduces your tax bill and reduces the income a mortgage lender will recognise. Two years of aggressive deductions can cost you more in borrowing power than they saved in tax. This is not a suggestion to overstate profit, but if you are self-employed and intend to buy in the next couple of years, that trade-off is worth discussing with your accountant before you file, not after.

The debts that behave strangely

Several common debts are not treated the way the statement suggests.

• Student loans in deferment or on an income-driven plan. A $0 payment is frequently not counted as $0. Depending on the loan programme, the lender may substitute a percentage of the outstanding balance instead. On a large balance that can add several hundred dollars a month to your ratio out of nowhere. Ask which figure will be used before you assume.
• Co-signed debts. If you co-signed for someone, the payment generally counts as yours, because you are legally liable for it. It can sometimes be excluded if you can evidence that the other party has made the payments from their own account for twelve months or more.
• Debts with only a few payments left. Some programmes let you exclude an instalment debt with fewer than about ten payments remaining. It is not automatic and it does not apply to leases, which are usually counted regardless because they tend to be replaced.
• 0% promotional finance. A furniture or phone plan at 0% is still a monthly obligation and still counts, even though it costs you nothing in interest.
• Authorised user cards. A card where you are an authorised user but not liable can often be excluded with evidence, though it may still appear on your credit file.
• Business debt paid by your company. Can sometimes be excluded if the business has paid it for twelve months and the payments come from business accounts.

The pattern is consistent: lenders care about legal liability and documented history. If a debt is legally yours, assume it counts until someone tells you otherwise in writing.

How does a joint application change the ratio?

When two people apply together, both incomes count and both sets of debts count. The ratio is calculated on the combined position, not on each person separately.

This produces a result that surprises couples: adding a second applicant does not always help. If one partner brings $900 a month of debt payments and $1,100 a month of income, they make the combined ratio worse, not better. The right question is not "should we both apply" but "does this person’s income exceed their debts by enough to improve the ratio".

Credit scores work differently again: many lenders use the lower of the two middle scores, so a partner with thin credit can affect your rate even when they improve the income side. Both questions are worth asking your loan officer explicitly, because the answer genuinely varies by situation.

What can you do if your ratio is too high?

Only two things move the ratio: payments down, or income up. What matters is picking the lever with the most leverage.

1. Target the biggest monthly payment, not the biggest balance. This is the opposite of how you would pay off debt to minimise interest, and it catches people out. On the example figures, clearing a $380 car payment takes the ratio from 36.3% to 30.0%. Clearing a $210 student loan only gets to 32.8%, even if you owe far more on it.
2. Pay a card down to shrink its minimum. Because the minimum is a percentage of the balance, paying it down lowers the figure the lender counts. This helps twice: less debt, and a smaller counted payment.
3. Do not open anything new. A car financed three months before applying has sunk more mortgage applications than almost anything else. So has furniture on finance for the house you have not bought yet.
4. Document income you already have. If you have two years of consistent overtime or a second job, make sure it is on the application. People routinely leave out income that would have counted.
5. Consider the timing. If a car loan has eight payments left, finishing it before you apply may remove it from the calculation entirely.

A word of caution about all of these. They make the ratio read better, and the ratio is a proxy for something real. Refinancing debts over a longer term lowers the monthly payment and improves the ratio while leaving you owing just as much for longer. That can be a reasonable short-term move and a poor permanent one. Be honest with yourself about which you are doing.

Getting the same number the lender gets

If you want your figure to match the underwriter’s, work from the documents they will use rather than from memory.

1. Pull your credit report and use the minimum payments listed on it. That is the source the lender uses, and it occasionally differs from what you believe you owe.
2. Use gross pay from your payslips or tax returns, not your bank statements.
3. For a mortgage, use the full proposed housing payment: principal, interest, property taxes, homeowner’s insurance, mortgage insurance if your deposit is under 20%, and any association dues. Quoting yourself the principal-and-interest figure from a rate advert is the most common reason a buyer’s own number is better than the lender’s by several points.
4. Calculate both ratios. The front-end ratio is housing alone against income; the back-end is everything. Lenders look at both, and most free calculators only give you one.

Then check it against the limits that actually exist. Fannie Mae caps manually underwritten loans at 36%, rising to 45% where the borrower meets its credit score and reserve requirements, and allows up to 50% through Desktop Underwriter. The widely repeated 43% "legal maximum" is out of date: the CFPB removed that cap and replaced it with a price-based test for applications received on or after 1 October 2022. It survives as a common internal guideline, not a rule.

One last thing worth saying plainly. A ratio that clears a threshold tells you a lender will probably say yes. It does not tell you the payment fits your life. Those are different findings, and only one of them is made by the bank.

Common questions

Sources

Reviewed on 23 Oct 2026 against the published sources below. Laws and prices change, so check the current position before you rely on a figure.

• Consumer Financial Protection Bureau: What is a debt-to-income ratio?
• Fannie Mae Selling Guide B3-6-02: Debt-to-Income Ratios
• Consumer Financial Protection Bureau: General QM loan definition final rule (a price-based test replaces the 43% limit)

The treatment of particular income types and debts described here reflects common agency and lender practice, and individual lenders apply their own stricter overlays. FHA, VA and USDA loans are assessed on their own rules. Always confirm how your own income and debts will be counted with the loan officer handling your application. General information, not mortgage advice.

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