Home Financing & Costs • Greater Seattle
Found A Home In Shoreline Or Bothell With A Basement Apartment Or Backyard Cottage? The Rent From That Extra Living Space Might Help You Qualify For The Mortgage.
Yes. Under qualifying FHA and Fannie Mae conventional loan programs, rental income from an accessory dwelling unit (ADU) can help with mortgage qualification. The calculation commonly starts with 75% of documented rent, subject to a 30% qualifying-income limitation and other loan-specific requirements. How that income is applied differs between FHA and conventional loans.
Imagine finding a $950,000 home in Bothell with a finished basement apartment. Your salary alone doesn’t quite qualify you for the loan, but the apartment could generate monthly rent.
Updated FHA and conventional lending guidelines make it possible for some buyers to use that rental income when qualifying for an owner-occupied home. The important questions are how much rent the lender accepts, whether the unit qualifies, and which loan program fits your situation.
How The 75% Rental Income Calculation Works
Example: A Seattle-area ADU with $2,000 in documented monthly market rent.
This is an illustrative calculation, not a loan approval or a promise that $1,500 will be added to your qualifying salary. The lender must also apply the program’s income limits, documentation rules, and applicable rental-income treatment.
Comparing Your Financing Options
How FHA And Conventional Loans Count ADU Rent
Both FHA and Fannie Mae conventional loans may allow rental income from an accessory dwelling unit to help qualify for a mortgage.
Both commonly begin with 75% of documented rent, allowing 25% for vacancy and expenses. But the way lenders apply that income is different.
| Rule | FHA Loan | Conventional (Fannie Mae) |
|---|---|---|
| Rental Income Calculation | Generally 75% of the lesser of documented market rent or applicable lease rent when there is limited rental history. | Generally 75% of supported gross rent, followed by a calculation that accounts for the property’s housing payment. |
| ADU Income Limit | No more than 30% of total monthly qualifying income. | No more than 30% of total qualifying income. |
| Rental Experience | Prior landlord experience is not generally required to use eligible ADU income under the applicable rules. | With less than 12 months of rental management experience, positive rental income can offset the housing payment only. |
| Documentation | Appraisal and comparable rent schedule, generally Form 1007, plus applicable lease documentation. | Appraisal-supported rent schedule and an executed lease when one transfers to the buyer. |
| Reserves | Generally two months of principal, interest, taxes, and insurance remaining after closing when qualifying with ADU rent. | Depends on the loan and underwriting requirements. |
| Eligible Transactions | Certain purchases and refinances, including qualifying 203(k) rehabilitation loans. Not cash-out refinances. | Purchases and limited cash-out refinances. Not cash-out refinances. |
These rules concern rental income from one qualifying ADU associated with a one-unit residence. Other property types and loan programs may follow different guidelines.
The Biggest Difference For First-Time Landlords
FHA: Eligible ADU rental income may be added to qualifying income under FHA’s rules, even without prior rental-property management experience.
Fannie Mae: With less than 12 months of rental management experience, positive rental income generally may only offset the property’s housing payment. It cannot simply be added to your salary as extra qualifying income.
That distinction can make a meaningful difference for someone buying their first home with an ADU.
Both loan programs also require an acceptable property and reliable rental-income documentation. The lender cannot simply use an owner’s estimate of what the ADU might earn.
If you’re considering a property in Shoreline, Bothell, Kirkland, or elsewhere in Greater Seattle, ask a lender to compare FHA and conventional underwriting before relying on the rental income.
You can review the rules in HUD Mortgagee Letter 2023-17 and the Fannie Mae Selling Guide .
A Realistic Financing Example
How Much Can ADU Income Help You Qualify?
Imagine you and your partner earn $11,000 per month and are considering a $950,000 home in Bothell with a finished basement apartment.
If an appraiser supports monthly ADU rent of $2,000, here’s how an eligible FHA rental-income calculation might work.
An Extra $1,500 In Potential Qualifying Income
FHA can generally count 75% of supported ADU rent when the applicable requirements are met.
In this example, $1,500 is below FHA’s 30% limit on ADU income as a share of total effective income.
The additional income may improve the borrower’s debt-to-income calculation, but it does not guarantee approval for the $950,000 property.
Why ADUs Are Becoming More Common In Washington
Washington’s House Bill 1337 expanded opportunities to build accessory dwelling units throughout the state.
In urban growth areas, most cities and counties must allow up to two ADUs on qualifying residential lots, subject to applicable site restrictions and development standards.
That creates more housing options for buyers who want a basement apartment, converted garage, or backyard cottage.
However, permission to build an ADU does not mean an existing unit automatically meets mortgage requirements.
What Must You Verify About The ADU?
- Permits And Legal Status: Confirm the unit’s approval with the local jurisdiction, including any applicable rental-use requirements.
- Appraisal Classification: Make sure the lender and appraiser recognize the space as an acceptable ADU under the loan program.
- Market Rent: Obtain supported rental estimates rather than relying only on the seller’s projections.
- Loan Requirements: Confirm income treatment, available reserves, and property eligibility with your lender before making an offer.
Before You Write An Offer
Five Things To Check Before Buying A Home With An ADU
Rental income can make a home more affordable, but don’t assume every basement apartment or backyard cottage will qualify. Check these details before relying on the rent.
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Verify The ADU’s Legal Status
Review city or county permits, approved use, and whether the space meets applicable property and lender requirements.
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Confirm The Market Rent
Ask the lender about the appraisal rent schedule and how an existing lease, if any, affects the accepted amount.
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Compare FHA And Conventional
Rental-management experience can change how conventional underwriting treats the income. Have a lender run both options.
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Check Your Cash Reserves
Ask how much money must remain after your down payment and closing costs. Requirements vary by loan program.
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Plan For Real Ownership Costs
Budget for maintenance, vacancies, insurance, utilities, and rental taxes. Qualifying for a loan is not the same as having positive monthly cash flow.
Watch Emily’s ADU Guide
ADU Vs. DADU: Should You Build One Or Buy A Home With One?
If you’re comparing existing ADU homes with properties where you could build one, this video covers Seattle zoning, construction costs, rental potential, and how to evaluate the investment.
The video focuses on the real estate side of ADUs. Your lender should confirm the separate mortgage qualification rules.
Common Buyer Questions
Frequently Asked Questions
How Much More House Can ADU Rental Income Help Me Afford?
It depends on your loan program, documented rent, existing debts, interest rate, and reserves. A lender can compare approvals with and without eligible ADU income. There is no guaranteed increase in purchasing power.
Do I Need An Existing Tenant And A Signed Lease?
Not always. Some purchase scenarios allow an appraisal-supported rent estimate without an existing tenant. If a lease is being transferred, additional documentation is required. Your lender will confirm the applicable rules.
Can I Use ADU Rental Income To Buy An Investment Property?
The FHA and Fannie Mae ADU provisions discussed here apply to qualifying one-unit primary residences with an accessory unit. Investment properties and duplexes have different rental-income rules.
Will I Owe Taxes On The ADU Rent?
Rental income you collect is generally taxable, although qualifying rental expenses and deductions may reduce taxable income. Consult a CPA before estimating your net return.
Could An ADU Help You Buy Your Next Seattle Home?
I help buyers across King and Snohomish Counties evaluate homes with ADUs, compare rental potential, and coordinate with local mortgage lenders.
Let’s look at your actual financing options before you make an offer. We Make Real Estate EASY For You.
Mortgage eligibility and use of rental income depend on underwriting guidelines, property eligibility, and lender approval. Rental estimates are not guaranteed income. Consult your lender and tax professional for advice specific to your situation.