ADU ROI Calculator and Cash-Out Refinance Loan Planner
Use your home equity to finance ADU construction. This calculator shows your projected rental income, break-even timeline, and total return on investment for accessory dwelling units in California and Washington.
Quick Answer: ADU ROI and ADU Loan Calculator
To estimate ADU ROI in 2026, compare total construction cost against expected rent, vacancy, financing payment, and property value increase. A cash-out refinance works best when the project needs a fixed-rate lump sum. A HELOC works best when you want staged draws and do not want to replace a low-rate first mortgage.
- Primary output: break-even timing and monthly cash flow
- Loan comparison: cash-out refinance, HELOC, and home equity loan
- Best use: garage conversion, detached ADU, or attached ADU planning
- Markets covered: California and Washington homeowner scenarios
| ADU Type | Avg. Cost (CA) | Avg. Cost (WA) | Sq. Ft. Range | Timeline |
|---|---|---|---|---|
| Garage Conversion | $80,000–$120,000 | $65,000–$100,000 | 400–600 sq ft | 3–4 months |
| Attached ADU | $150,000–$250,000 | $130,000–$220,000 | 600–1,000 sq ft | 5–8 months |
| Detached ADU | $200,000–$350,000 | $175,000–$300,000 | 600–1,200 sq ft | 6–10 months |
| Prefab/Modular ADU | $120,000–$200,000 | $100,000–$180,000 | 400–800 sq ft | 2–4 months |
| Feature | Conventional Cash-Out | FHA Cash-Out | HELOC Alternative |
|---|---|---|---|
| Max LTV | 80% | 85% | 90% CLTV |
| Min Credit Score | 620 | 580 | 680 |
| Rate Range (Feb 2026) | 6.25–7.00% | 5.875–6.50% | 7.50–9.00% variable |
| Disbursement | Lump sum at closing | Lump sum at closing | Draw as needed |
| Best For | Large equity, fixed rate | Lower credit, higher LTV | Smaller projects, flexibility |
| Region | Studio/1-Bed | 2-Bed ADU | Avg. Vacancy | Annual Gross |
|---|---|---|---|---|
| Orange County, CA | $2,200–$2,800/mo | $2,800–$3,500/mo | 3–5% | $31,680–$40,320 |
| Los Angeles County, CA | $1,800–$2,500/mo | $2,500–$3,200/mo | 4–6% | $24,192–$36,864 |
| San Diego County, CA | $1,900–$2,600/mo | $2,600–$3,300/mo | 3–5% | $27,360–$37,620 |
| King County, WA | $1,700–$2,300/mo | $2,300–$3,000/mo | 3–5% | $24,480–$34,200 |
| San Francisco, CA | $2,500–$3,200/mo | $3,200–$4,000/mo | 4–6% | $33,600–$46,080 |
Cash-Out ADU ROI Calculator
Educational estimate only. The refinance rate used is hypothetical and does not represent a current rate offer. Actual costs, rents, rates, and financing terms vary based on creditworthiness, loan amount, property type, and market conditions. Not a commitment to lend. Consult a licensed contractor and mortgage broker for project-specific analysis. NMLS #1426884 | Lumin Lending NMLS #2716106.
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ADU Financing FAQ
How does this ADU ROI calculator estimate return?
This ADU ROI calculator compares estimated construction cost, financing cost, market rent, vacancy, and expected property value increase. It is designed to show break-even timing, monthly cash flow, and whether a cash-out refinance or separate ADU loan is likely to be more practical.
Can I use an ADU loan calculator to compare cash-out refinance and HELOC options?
Yes. For ADU projects, the useful comparison is available equity, interest rate, payment type, total funds needed, and whether you need all funds at closing. Cash-out refinance often works for large projects that need lump-sum funding, while a HELOC can work for staged draws on smaller projects.
Can I use a cash-out refinance to build an ADU in California?
Yes. California homeowners with sufficient equity use cash-out refinancing to fund ADU construction at mortgage rates, which are often lower than construction loan rates. You typically need to keep at least 20% equity after the refinance for conventional cash-out financing.
How long does it take to break even on an ADU investment?
Most homeowners in high-demand California and Washington markets break even in 5 to 8 years on ADU construction financed through cash-out refinance. The timeline depends on construction cost, monthly rent, vacancy, property taxes, insurance, and the interest rate on your financing.
Does building an ADU increase my property value?
A permitted ADU can add meaningful property value in California and Washington markets because it adds legal living area and potential rental income. The exact value increase depends on local rent demand, appraisal treatment, ADU quality, and whether the unit is permitted.
Is a HELOC or cash-out refinance better for funding an ADU?
Cash-out refinance is usually stronger for larger ADU projects that need a fixed-rate lump sum. A HELOC can be better when your current first mortgage rate is low or the project needs staged draws. The right choice depends on your existing rate, equity, project budget, and payment tolerance.
Have questions about ADU financing? Call Mo at (949) 579-2057 · NMLS #1426884 · Lumin Lending NMLS #2716106
Key Takeaways
- California SB 9 allows homeowners to build ADUs on single-family lots statewide, bypassing local zoning restrictions since January 2022.
- Washington HB 1110 requires cities with 25,000+ residents to permit at least 2 ADUs per residential lot effective June 2025.
- The Equity-to-Debt Arbitrage Strategy (cash-out refinance for ADU construction) provides lump-sum financing at mortgage rates (6.0-7.0%) versus construction loan rates (8-12%), turning idle equity into income-producing square footage.
- Orange County ADU rental income averages $2,200-$3,500/month depending on unit size, adding 15-25% to property value.