Mortgage lenders calculate your income by taking every stable, documented source of money you earn, converting it into one gross monthly number using fixed formulas, and then measuring your debts against that number through a debt-to-income (DTI) ratio. The arithmetic looks simple at the end, but the work sits in deciding which dollars qualify, how to average income that moves around, and how much of certain streams (like rent) the lender will actually credit you with.
Income That Qualifies, Income That Doesn’t
Lenders are looking for income that is stable, documented, and reasonably expected to continue. If a particular stream has a known expiration date, it generally needs to last at least three years from the date of your mortgage note to count.1Fannie Mae. B3-3.1-01, General Income Information
Base salary and hourly wages from a primary job are the most straightforward. Beyond that, lenders count bonuses, overtime, commissions, and tips when you have a consistent track record of receiving them. Social Security benefits, pensions, court-ordered alimony and child support, dividends, interest, and rental income can all qualify too.1Fannie Mae. B3-3.1-01, General Income Information
What doesn’t count: one-time windfalls such as lottery winnings, inheritances, or cash gifts. Temporary unemployment benefits are excluded because they lack continuity. Income that can’t be documented, such as cash payments without tax records, doesn’t exist in the underwriting world.
How Each Type of Income Gets Converted to a Monthly Number
Salaried and Hourly Workers
Fixed salary is annual pay divided by 12. Hourly workers with a steady schedule get their weekly gross multiplied by 52, then divided by 12. Biweekly pay is multiplied by 26 and divided by 12. Semi-monthly pay (twice a month on set dates) is multiplied by 24. Biweekly and semi-monthly aren’t the same thing, and using the wrong multiplier misstates income by roughly 8%.
Bonuses, Overtime, Commissions, and Tips
When earnings fluctuate, the underwriter averages the most recent two years. If the trend is flat or rising, you get the two-year average. If the most recent year is lower, the lender typically uses that lower figure rather than the midpoint, on the view that a downward trend predicts future earnings better than an average does.2Fannie Mae. Bonus, Commission, Overtime, and Tip Income Seasonal work follows the same logic: two years of earnings divided by 24 months, with proof that the cycle will continue.
Self-Employment
Self-employed borrowers face the most scrutiny. The lender starts with net profit from your tax returns, typically Schedule C for sole proprietors, then adds back certain non-cash deductions that reduced taxable income but didn’t actually leave your bank account. Depreciation, depletion, and amortization are the usual add-backs.3Fannie Mae. Cash Flow Analysis (Form 1084) If you reported $80,000 in net profit and $15,000 in depreciation on equipment, your qualifying cash flow is closer to $95,000. Two years of returns are standard, and a declining year gets used instead of the average, just like with variable wage income.
Rental Income
If you own rental property, you don’t get credit for 100% of the rent. Fannie Mae’s automated underwriting applies a 25% reduction to gross rent to cover vacancies, maintenance, and management. For an investment property, qualifying income is 75% of gross rent minus the full monthly payment on that property (principal, interest, taxes, insurance, and association dues). For a two-to-four-unit home you live in, it’s 75% of gross rent from the non-owner units.4Fannie Mae. Income from Rental Property in DU
The 25% haircut surprises many borrowers. Collect $2,000 a month on an investment property with a $1,200 payment, and only $300 lands in your qualifying total, not the $800 you might expect.
Documentation the Lender Will Ask For
Your financial picture gets captured on the Uniform Residential Loan Application (Fannie Mae Form 1003).5Fannie Mae. Uniform Residential Loan Application (Form 1003) From there, every income source listed needs backup.
Wage earners provide a recent pay stub dated no more than 30 days before application, showing year-to-date earnings, along with W-2 forms covering one or two years depending on the income type.6Fannie Mae. Standards for Employment and Income Documentation Self-employed borrowers and anyone with complex finances supply full federal tax returns (Form 1040) with all relevant schedules. Underwriters look at specific line items, including Adjusted Gross Income on line 11.
Social Security and disability recipients should request a benefit verification letter through the SSA; that letter is the standard proof of benefit income on a loan file.7Social Security Administration. Get Benefit Verification Letter Investment income usually calls for recent 1099 forms and brokerage statements.
Lenders verify employment on their own too. They can send a written verification (Fannie Mae Form 1005) to your employer’s HR department to confirm position, start date, and likelihood of continued employment, and a separate verbal verification is required within 10 business days of closing.8Fannie Mae. B3-3.1-04, Verbal Verification of Employment
How That Income Gets Tested Against Your Debts
Once the lender has a gross monthly income figure, it runs two DTI ratios. The front-end ratio (the housing ratio) divides proposed monthly housing costs (mortgage payment, property taxes, homeowner’s insurance, and any association dues) by gross monthly income. A common soft benchmark sits at 28% to 31%, though it isn’t a hard cutoff for most programs.
The back-end ratio is the one that matters most. It takes all recurring monthly debts plus the proposed housing payment, divided by gross monthly income. Earn $8,000 a month with total debts (including the new mortgage) of $3,200, and your back-end DTI is 40%.
What Shows Up on the Debt Side
Car loans, credit card minimums, personal loans, and existing mortgage payments all count. So do some obligations that don’t appear on a credit pull.
Student loans cause the most problems. If you’re on an income-driven plan and the credit report shows your actual payment, that’s what the lender uses, even if it’s $0. If your loans are in deferment or forbearance with no payment reporting, the lender has to calculate one: either 1% of the outstanding balance or a fully amortizing payment based on the loan’s repayment terms.9Fannie Mae. Monthly Debt Obligations A $40,000 balance in deferment generates a $400 monthly obligation under the 1% rule, which can single-handedly push you over the limit.
Court-ordered alimony and child support that will continue more than ten months count as recurring debt. For alimony specifically, the lender can either add the payment to debts or subtract it from income; the DTI comes out the same either way.9Fannie Mae. Monthly Debt Obligations Child support must be treated as a debt, with no income-side option.
A 401(k) loan won’t appear on your credit report, but the lender can see the repayments on your pay stubs and may factor them into DTI anyway. The same goes for other payroll-deducted obligations.
DTI Ceilings by Loan Type
Conventional Loans
Fannie Mae’s baseline for manually underwritten loans is 36%, stretching to 45% with specific credit score and reserve requirements. Most conventional loans run through the Desktop Underwriter (DU) automated system, where the maximum DTI can reach 50%.10Fannie Mae. Debt-to-Income Ratios Reaching that ceiling takes strong compensating factors: a high credit score, significant cash reserves, or a large down payment. Individual lenders may set their own lower caps.
FHA Loans
FHA standards are more flexible. The front-end limit is 31% and the back-end is 43% under standard guidelines, but loans run through FHA’s automated underwriting (TOTAL Scorecard) can go as high as 57% on the back end for borrowers with strong overall profiles. Manual underwriting allows 43% to 50% with documented compensating factors.
VA Loans
The VA has no hard DTI cap. It uses 41% as a guideline, and borrowers above that threshold face additional review but aren’t automatically disqualified. The real test is residual income: what’s left after the mortgage, all debts, taxes, and essential living expenses. Required residual income varies by family size and region, and borrowers above 41% DTI typically need to exceed the residual income guideline by at least 20%.
If Your Own Income Falls Short
Adding a non-occupant co-borrower, such as a parent, is a common fix for a high DTI. Fannie Mae allows the income and debts of all borrowers to be combined into one DTI through automated underwriting, with no separate DTI requirement for the occupant borrower.11Fannie Mae. Non-Occupant Borrowers On a manually underwritten loan, the occupant must still qualify at 43% DTI or less on their own income and debts. The co-borrower’s existing debts come along too, so a high earner with heavy obligations doesn’t help as much as the raw income number suggests.
The 43% QM Rule No Longer Applies
You may still see references to a 43% DTI cap tied to the Qualified Mortgage rule. That rule is outdated. In December 2020, the Consumer Financial Protection Bureau replaced the 43% hard cap with a price-based test: a loan qualifies as a General Qualified Mortgage if its annual percentage rate doesn’t exceed the average prime offer rate for a comparable loan by more than 2.25 percentage points.12eCFR. 12 CFR 1026.43 – Minimum Standards for Transactions Secured by a Dwelling The mandatory compliance date was July 1, 2021.13Consumer Financial Protection Bureau. General QM Loan Definition Final Rule
Lenders still have to consider DTI as part of the broader Ability-to-Repay analysis under Dodd-Frank. They must verify your income, debts, and monthly obligations, and make a good-faith determination that you can repay. The practical DTI limits you’ll run into come from the individual loan programs described above, not from the QM rule.