When you go to buy unit number two, the rental income from unit number one can either carry the deal or sink it, and which way it goes is decided almost entirely by paperwork. Lenders do not take your word for what a property earns. They want a lease, a rent history, and the Schedule E from your last tax return, and they run those documents through a formula that is far less generous than the rent check you actually deposit. Understanding that formula before you apply is the difference between qualifying for the next building and getting told to come back next year.
Almost every page that ranks for this is written by someone selling you the loan, or it is the raw Fannie Mae guideline, which reads like tax code. This is the same rules translated from the side of the landlord who has to hand over the records: what the 75% haircut really does to your numbers, why your tax return can quietly count against you, and what kind of bookkeeping makes the math land in your favor. The figures below reflect Fannie Mae's selling guide as of June 2026; lender overlays and guideline updates move these rules, so confirm the current version before you apply.
The 75% rule, in plain terms
The headline number every landlord hears is 75%. When a property has no tax-return history yet, a conventional lender counts 75% of the gross rent toward your qualifying income and treats the remaining 25% as a built-in allowance for vacancy and maintenance. It does not matter that your actual vacancy last year was zero. The 25% haircut is structural, baked into Fannie Mae's selling guide so that one good year does not let a borrower over-qualify on rent that may not hold.
qualifying rent = 0.75 × gross monthly rent
Say you own a duplex where each side rents for $1,400, so $2,800 a month gross. The lender counts $2,100 of that, not $2,800. The missing $700 is gone for qualifying purposes, even though it lands in your account every month. That credited rent is then either added to your income or used to offset the mortgage payment on that property, depending on whether the property is your primary residence or a pure investment. On an investment property you already rent out, the rent first offsets that property's own payment, and only a net positive adds to your income.
When the lender uses Schedule E instead
The 75% gross-rent method is for properties without a filing history. Once a rental has appeared on a tax return, the rules change: the lender works from Schedule E, the form where you report rental income and expenses line by line. They take your net rental income or loss from that schedule and then add back the deductions that did not actually cost you cash that year, chiefly depreciation and, often, mortgage interest, plus a few items like one-time repairs and amortized costs.
The point of the add-backs is to reconstruct real cash flow. A rental can show a paper loss on Schedule E because depreciation is a non-cash deduction: you write off 27.5 years of building basis without spending a dime that year. The underwriter adds that depreciation back so it does not count against your income. If your books are sloppy and you missed depreciation entirely, you lose that add-back and your qualifying income drops for no good reason. This is one of several places where forgotten depreciation quietly costs you twice.
Worked through: suppose Schedule E shows $16,800 of rent received, $9,000 of operating expenses, $6,000 of mortgage interest, and $5,200 of depreciation, for a reported net loss of $3,400. The lender starts at that −$3,400, adds back the $5,200 depreciation and the $6,000 interest, and arrives at roughly $7,800 of annual qualifying income, or $650 a month. The property that looked like a loss on your return becomes positive income to the underwriter, which is exactly why the add-backs matter.
Why your tax return can work against you
Here is the trap that catches self-managers. Many landlords are coached to minimize taxable income, so they claim every deduction and report the smallest legal profit. That is fine for the IRS, but the same return is what the mortgage underwriter reads, and a return engineered to show near-zero income gives them near-zero income to count. The deductions that are non-cash get added back; the ones that represent real spending do not.
- Under-reported rent costs you the most. If you collected $1,400 but recorded $1,200 because the bookkeeping drifted, the lender sees $1,200. There is no add-back for rent you simply did not write down.
- Real cash expenses lower your counted income. Insurance, property taxes, management fees, and ordinary repairs are genuine outflows, so they are not added back. Classify a true improvement as a repair and you have just lowered your qualifying income, on top of the tax issue covered in repairs versus improvements.
- One bad year of records can stall the next purchase. The underwriter wants the rent history to be clean and continuous. A gap, an unexplained dip, or a lease that does not match the deposits invites questions that slow or kill an approval.
The fix is not to over-report income to the IRS. It is to keep records accurate enough that the income you genuinely earned is visible and documented. Complete books usually mean more counted income, because nothing real falls through the cracks.
The documents a lender will ask for
Whether the property is seasoned or brand new, the request list is predictable. Have these ready before you apply and the file moves faster.
- Current signed leases for every unit. The lease establishes the rent the lender will use when there is no tax-return history, and it has to match the deposits showing in your bank statements.
- Schedule E from your most recent return. For any property you have owned through at least one tax year, this is the primary source for the income calculation.
- Form 1007 or Form 1025. The appraiser completes the Single-Family Comparable Rent Schedule (Form 1007) or the small residential income property appraisal (Form 1025) to set market rent. Lenders generally use the lower of the appraised market rent and your actual lease rent.
- A rent roll and twelve months of payment history. Not always required, but it resolves disputes fast when the lease, the deposits, and the Schedule E do not line up at a glance.
The market-rent question is its own skill. Before you ever sit in front of an underwriter, it pays to know what your units should rent for, the same way you would pull rent comps yourself rather than trust a listing's hopeful number.
How this fits your financing plan
The 75% rule is what lets a buy-and-hold investor keep moving. Each property you season adds documented income that helps qualify for the next one, which is the mechanical engine behind a small portfolio that grows past two or three doors. The flip side is that every new mortgage stacks debt against that income, so the debt-to-income math and your debt service coverage ratio tighten as you scale. This page is about counting income on a conventional loan; if your tax returns are working against you, a property-qualified loan can be the cleaner path, which the wider guide to financing a rental property lays out alongside conventional and DSCR options.
If you are buying an owner-occupied multifamily, the rental-income rules shift, because you live in the building and a different set of agency tests applies. That projected-rent case is covered in house hacking financing rather than repeated here, so cross-read it if your next purchase is a duplex you plan to live in.
Where the records come from
Everything an underwriter wants comes down to a clean, continuous record of what each unit charged and what you collected, tied to a tax schedule that does not leave money on the table. That is the seam rents.ai is built for: it keeps a rent roll with per-tenant payment history, splits each mortgage payment into deductible interest, non-deductible principal, and escrow, and produces a Schedule E rollup and CSV export you can hand to your CPA or your lender. What it will not do is pull your rate, talk to an underwriter, or file the loan; the financing itself stays entirely in your hands and your lender's. Before you apply, run the property through a cash-on-cash calculator on the actual cash going in, and read tracking mortgage interest, principal, and escrow so the interest the lender adds back matches what you reported. The borrower with the tidy paper file gets the loan; the one reconstructing a year of rent from memory gets the delay.
The primary sources here are Fannie Mae's selling guide section B3-3.8-01, Rental Income, which governs the calculation, and the appraisal forms that set market rent, Form 1007 and Form 1025. Read those alongside your lender's own overlays before you count on any number above.
Rental-income credit percentages, add-back rules, and documentation requirements are set by Fannie Mae and individual lenders and change over time; confirm the current Fannie Mae selling guide and your lender's overlays before you apply. The worked examples are illustrative, not a quote. Nothing here is lending, tax, or legal advice.