ADU Project Calculator
Model your ADU project from budget to cash flow. Compare All Cash vs. HELOC vs. cash-out refinance financing, estimate rental income, and see the projected return on your investment — before breaking ground.
Get Started in 3 Steps
How to Use the ADU Project Calculator
Enter Your Property & Existing Debt
Input your home's current value, existing mortgage balance and rate, to establish your available equity and current monthly obligation.
Build Your ADU Budget
Break out every cost line — permits, design, site prep, construction, landscaping, and contingency — for an accurate total project budget.
Choose Your Financing & Project Rent
Select All Cash, HELOC, or Cash-Out Refi, enter your expected ADU monthly rent, and instantly see cash flow, ROI, payback period, and DSCR.
ADU Project Calculator
Current Home Equity
· 60.0% LTV$300,000
Total Project Cost
$209,000
Gross Monthly Rent
$1,800
Paying full project cost in cash. To model financing, select the Refinance or Purch. / Const. tabs.
Cash Needed at Closing
$209,000
Project Summary
Total Cost
$209,000
Cash Invested
$209,000
Added Payment
$0
ADU Rent (eff.)
+$1,800
New Total Monthly Payment
$3,500/mo
Before ADU
$3,500/mo
Project Profitability Analysis
Cash-on-Cash
10.3%
annual cash ÷ cash in
10.3%
cash flow + appreciation + recapture
ROE
7.2%
Projected Home Value
$959,000
current value + project cost
Projected Equity
$509,000
after new financing
Cash Invested
$209,000
out-of-pocket basis
Existing Equity
$300,000
before ADU build
Ready to make your project a reality? Schedule an ADU Financing Consultation
Model build costs, interest-only draws, and permanent financing for new construction or major renovations.
Check your debt-to-income ratio against lender guidelines — essential for qualifying on any loan program.
Analyze rental property cash flow and debt-service coverage — the key metric for investor loan qualification.
How much does it cost to build an ADU in Oregon?
ADU construction costs in Oregon typically range from $150,000 to $400,000+ depending on type (detached, attached, garage conversion, JADU), size, finishes, and location. Rental income of $1,500-$2,500/month is common depending on size and neighborhood.
Best for: Oregon and California homeowners considering adding rental income through an accessory dwelling unit
How It Works
Understanding the ADU Project Calculator
An Accessory Dwelling Unit (ADU) is one of the most effective ways to add rental income and property value to your existing home. This calculator breaks out every project cost line and models three financing scenarios (all cash, HELOC, or cash-out refinance) to show your return on investment.
Worked example: Your Portland home is worth $650,000 with a $300,000 mortgage at 3.50%. You want to build a 600 sq ft detached ADU with a $280,000 total budget. Using a HELOC at 8.00%, your ADU financing cost is approximately $1,867/month during repayment. If the ADU rents for $2,200/month, your net cash flow is +$333/month, and the DSCR on the ADU is 1.18. Payback period: approximately 10.6 years.
The calculator models HELOC vs. cash-out refi side by side so you can see which preserves more monthly cash flow. If you used a cash-out refi, you'd replace your 3.50% first mortgage at current rates — the monthly payment jump may offset the ADU income benefit.
Ready to apply?
Numbers look right? Explore our ADU Loans page for eligibility details, rates, and next steps.
About This Calculator
What the ADU Project Calculator is For
Adding an ADU is one of the highest-ROI improvements an Oregon homeowner can make — but the math requires modeling both sides of the ledger simultaneously: the full project cost (permits, design, construction, contingency), how you're financing it (cash, HELOC, or cash-out refi), and what the ADU will actually generate in rent net of vacancy and management. This calculator ties all of it together. Enter your existing property details and debt, break out every line of your CapEx budget, choose your financing method, and project your ADU rent to see your DSCR, monthly cash flow impact, cash-on-cash ROI, payback period, and a GRM-based value estimate side by side.
Common Use Cases
- Deciding whether to cash-out refi or use a HELOC to fund an ADU build
- Modeling net monthly gain from ADU rent vs. additional debt service before committing to a project
- Estimating cash-on-cash ROI and payback period to compare ADU investment against other uses of capital
Ready to turn numbers into a loan?
Common Questions
ADU Project Calculator — Frequently Asked Questions
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From the Blog
Further Reading
Loan TypesADUs for Multigenerational Households: Benefits, Considerations & Financing Options
More families are choosing to live under one roof — or at least on one property. An accessory dwelling unit lets you keep loved ones close while preserving the independence everyone needs. Here's how to think about the benefits, the planning process, and the financing.
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All calculator results are estimates for informational purposes only and do not constitute a loan commitment or guarantee of any specific rate or terms. Actual loan terms will depend on creditworthiness, property type, and market conditions. Lumen Mortgage Corporation · NMLS #1498678 · Licensed in Oregon & California · 920 SW 6th Ave, Suite 1200, Portland, OR 97204.