Conventional loan DTI limits top out at 50% for loans run through Fannie Mae’s Desktop Underwriter and 65% for loans run through Freddie Mac’s Loan Product Advisor. Those ceilings drop sharply when a loan is manually underwritten: Fannie Mae starts at 36% and stretches to 45% only when credit and reserves are strong. The number that governs approval is your back-end DTI, which stacks every monthly debt payment, including the new mortgage, against your gross monthly income.
How DTI Is Calculated
Divide your total monthly debt payments by your gross monthly income, then multiply by 100. If you earn $8,000 per month before taxes and your monthly debt payments including the proposed mortgage add up to $3,200, your DTI is 40%.
Lenders look at two versions. The front-end ratio, sometimes called the housing ratio, includes only your proposed mortgage payment: principal, interest, property taxes, homeowners insurance, any private mortgage insurance, and homeowners association dues.1Fannie Mae. Fannie Mae Selling Guide – B3-6-02, Debt-to-Income Ratios The back-end ratio adds every other recurring debt on top of that housing payment. Neither Fannie Mae nor Freddie Mac sets a separate maximum for the front-end ratio, so the back-end number is what drives approval.2Freddie Mac. Guide Section 4302.5
What Counts Toward Your Monthly Debt
Your back-end DTI captures every recurring obligation on your credit report, plus certain court-ordered payments:
- Credit card minimum payments. If the report doesn’t show a minimum, the lender uses 5% of the outstanding balance.
- Installment loans such as auto loans, personal loans, and timeshare payments, when more than ten monthly payments remain.
- Student loan payments shown on your credit report, or a calculated amount if the report shows zero.
- Alimony and child support that continue for more than ten months.
- The proposed mortgage: principal, interest, taxes, insurance, PMI, and any HOA dues.
Those obligations are documented in Fannie Mae’s monthly debt obligations guidelines.3Fannie Mae. Fannie Mae Selling Guide – Monthly Debt Obligations
Several common expenses are deliberately left out. Utility bills, groceries, car insurance, cell phone plans, and health insurance premiums are treated as living expenses, not credit obligations, so they don’t count. High living costs won’t directly block your approval, though they obviously affect what you actually have in your account each month.
The 10-Month Installment Rule
Installment debts with ten or fewer payments left can be excluded from your DTI. If you have a car loan with nine payments remaining, your lender can drop that payment from the calculation entirely, which can push a borderline application under the ceiling.3Fannie Mae. Fannie Mae Selling Guide – Monthly Debt Obligations
There is a catch. Even with ten or fewer payments to go, the lender must still count the debt if the payment materially affects your ability to handle your obligations. A $75 payment on an almost paid-off personal loan is easy to exclude. A $900 car payment with eight months left is harder to ignore, especially against a modest income. Lenders tend to use that discretion conservatively.
Fannie Mae DTI Limits
For loans underwritten through Desktop Underwriter, the maximum DTI is 50%. DU weighs your entire risk profile, including credit score, reserves, and down payment, and will approve ratios up to that ceiling when compensating factors support it.1Fannie Mae. Fannie Mae Selling Guide – B3-6-02, Debt-to-Income Ratios
For manually underwritten loans, the baseline is 36%. Fannie Mae allows a stretch to 45% when the borrower meets specific credit score and reserve thresholds in the Eligibility Matrix.4Fannie Mae. Eligibility Matrix For a one-unit purchase or rate-and-term refinance, you generally need a credit score of at least 660 to 700 (depending on loan-to-value) and six months of reserves to reach 45%. Three- and four-unit properties require higher scores and up to twelve months of reserves.
Freddie Mac DTI Limits
Freddie Mac is more generous on the automated side. Loans underwritten through Loan Product Advisor can qualify with a DTI up to 65%.2Freddie Mac. Guide Section 4302.5 A 65% approval is not easy to get. LPA weighs the full risk picture, and a borrower at that level would need exceptional compensating factors: a high credit score, substantial reserves, or a low loan-to-value ratio. The higher ceiling still gives Freddie Mac lenders more room to work with borrowers who have high income and high fixed obligations.
When a loan doesn’t earn an automated approval, Freddie Mac’s manual underwriting standards apply, with tighter limits similar to Fannie Mae’s manual thresholds.
Why Automated Underwriting Drives Approvals
Most conventional loans today go through automated underwriting, and the system’s decision matters more than any single DTI number. Desktop Underwriter and Loan Product Advisor don’t just check whether your ratio sits below a cutoff. They run a comprehensive risk analysis that weighs credit history, liquid assets, down payment size, loan type, and property characteristics against each other.5Fannie Mae. Desktop Underwriter and Desktop Originator6Freddie Mac Single-Family. Loan Product Advisor
Two borrowers with identical DTI ratios can get opposite results. A borrower at 48% with a 780 credit score, six months of mortgage payments in savings, and 20% down has a fundamentally different risk profile than someone at 48% with a 680 score, minimal reserves, and 5% down. The automated system sees that difference instantly. When it encounters a DTI above the normal comfort zone, it looks for compensating factors to justify the approval. Strong credit scores and cash reserves after closing carry the most weight.
h2>Student Loans: Where the Two Agencies Diverge
Student loan treatment is where Fannie Mae and Freddie Mac rules create the biggest practical difference. If your credit report shows a monthly student loan payment, both agencies use that number. The divergence happens when the credit report shows a zero payment, common for borrowers in income-driven repayment or deferment.
Fannie Mae requires the lender to use either 1% of the outstanding balance or a fully amortizing payment calculated from the loan’s actual terms.3Fannie Mae. Fannie Mae Selling Guide – Monthly Debt Obligations On a $50,000 student loan balance, that’s $500 per month added to your DTI even if your actual payment is zero. One exception: if the borrower is on an income-driven plan and can document the actual payment is $0, the lender may qualify the borrower with a $0 payment.
Freddie Mac uses 0.5% of the outstanding balance when the credit report shows zero.7Freddie Mac. Guide Section 5401.2 That same $50,000 balance counts as $250 per month instead of $500. For income-driven plan borrowers whose documented payment will increase after recertification, Freddie Mac uses the greater of the current payment or 0.5% of the balance. This difference alone can swing a borderline approval. Borrowers with large student loan balances should ask their lender which agency’s guidelines produce the better ratio.
Excluding Debt Paid by Someone Else
If you are obligated on a debt but someone else has been making the payments, you may be able to drop it from your DTI. The person paying cannot be an interested party to the transaction, such as the seller or real estate agent.3Fannie Mae. Fannie Mae Selling Guide – Monthly Debt Obligations
For non-mortgage debts like car loans, student loans, or credit cards, the lender needs twelve months of canceled checks or bank statements from the person actually making the payments, with no late payments during that period. For mortgage debts, the requirements tighten: the person paying must also be obligated on the mortgage, there can’t be any delinquencies in the most recent twelve months, and the borrower can’t be using rental income from that property to qualify.
This comes up often when divorced borrowers still appear on a joint auto loan or mortgage that an ex-spouse is paying. Pulling those twelve months of documentation together before you apply saves real time in underwriting.
Community Property States
If the property you’re buying sits in a community property state, your spouse’s debts can count against your DTI even if your spouse is not on the loan. The nine community property states are Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin. Alaska, South Dakota, and Tennessee offer opt-in community property systems.
In these states, the lender pulls a credit report on the non-borrowing spouse and includes their debt obligations unless state law provides a basis for excluding them. The spouse’s credit score isn’t used and can’t be a reason for denial, but their debts affect the math. Applying without your spouse in a community property state? Review the spouse’s credit report early to avoid surprises during underwriting.
How to Lower Your DTI Before Applying
If your DTI is too high, the most direct fix is paying down revolving debt. Credit cards drive DTI through their minimum payments, so even moderate paydowns can meaningfully lower your ratio. Paying a credit card balance from $5,000 down to $1,000 might drop the minimum payment from $150 to $25, shaving $125 off your monthly obligations.
A few other moves that work:
- Get all your documented income on paper. If overtime or bonus income isn’t consistently reflected on your pay stubs, fix that before you apply. A raise or a higher-paying job directly improves the ratio.
- Avoid new credit. Opening a new credit card or auto loan before your mortgage application adds to your monthly obligations and can drop your credit score.
- Time the application around the 10-month rule. If an installment loan will have ten or fewer payments remaining by the time you close, waiting a few months could take that payment off your DTI entirely.
- Ask about Freddie Mac pricing. If your student loan balances are high and payments show as zero on your credit report, Freddie Mac’s 0.5% calculation versus Fannie Mae’s 1% could meaningfully change your ratio.
Refinancing or consolidating existing debts into a lower monthly payment can also reduce DTI, but taking on new credit right before a mortgage application carries its own risks. Talk through the timing with your loan officer before making any moves.