The question behind every ADU conversation isn’t really “what does it cost?” — it’s “what will my monthly payment be, and will the rent cover it?” Here’s the honest 2026 answer for California homeowners.
The Monthly Payment Math
Take a typical $250,000 ADU project financed at October 2026 rates:
| Loan type | Rate used | Monthly payment |
|---|---|---|
| 30-year fixed at 7.40% | 7.40% | $1,731/mo principal + interest |
| 30-year fixed at 7.00% | 7.00% | $1,663/mo principal + interest |
| 15-year fixed at 6.73% | 6.73% | $2,210/mo principal + interest |
| HELOC (interest-only) | 8.02% | $1,671/mo interest only |
Now the key context: Southern California ADUs typically rent for $1,800–$2,800+/month. In many cases the rental income covers — or nearly covers — the loan payment. That’s the core of the ADU financing case.
Your Financing Options Compared (2026)
| Option | Typical terms | Best for |
|---|---|---|
| HELOC / home equity loan | HELOC ~7.3–8.0%; equity loans ~8.2%; usually up to 80–90% combined loan-to-value | Most homeowners — keeps your existing low-rate first mortgage untouched. The most common ADU funding route. |
| Fannie Mae HomeStyle | 3% down (primary residence), 620+ credit, based on as-completed appraised value; up to 50% of funds disbursable upfront | Buyers and owners who want renovation + ADU in one loan; covers ADUs explicitly, including second homes |
| FHA 203(k) | 3.5% down, primary residence only | Lower-credit buyers building on their own lot |
| Construction-to-permanent loan | 7–10% rates, 20–25% down, 680+ credit | Larger projects; converts to a mortgage when building is done |
| ADU-specialty lenders | Streamlined ADU loans, some with 10–15% down | Borrowers who want a lender that understands ADUs (projected-rent underwriting) |
| Cash-out refinance | ~7.4% 30-yr fixed (Oct 2026) | Usually the worst option — refinancing means giving up a sub-4.5% first mortgage, which most homeowners still hold |
Can Projected Rent Count Toward Your Loan?
Yes — this changed the game. Under Fannie Mae’s 2026 guidelines, projected rental income from one ADU can count toward mortgage qualification — capped at 30% of your total qualifying income on an owner-occupied one-unit property. Fannie now also allows financing up to two ADUs on a one-unit property. Traditional banks may still want 12+ months of documented rental history, but specialty ADU lenders underwrite on projected comps.
What About the CalHFA ADU Grant?
Be careful here: the CalHFA ADU Grant (up to $40,000 for pre-development costs) is not funding new applications in 2026 — the last round was fully allocated in late 2023. CalHFA warns that anyone claiming they can still secure it for you may be running a scam. Don’t build your budget around grant money that isn’t currently available.
Fee Breaks That Actually Exist
- Under 750 sq ft: state law (SB 13) exempts most ADUs from impact fees — worth $5,000–$15,000.
- LA’s pre-approved plans: using the city’s standard plans skips much of plan check (and one city-owned plan is free).
- LA’s AB 2533 amnesty (mid-2026): penalty-free legalization of pre-2020 unpermitted ADUs, with most impact fees waived.
The Honest Bottom Line
Most of our clients finance with a HELOC, keep their low first-mortgage rate, and let the ADU’s rent carry most or all of the payment. The projects that work are the ones where the math was done before construction started — real build cost, real monthly payment, realistic rent. That’s exactly what we map out in a free consultation.
Know Your Number Before You Build
We help every client map the full financial picture — real construction cost, real monthly payment, and realistic rental income — before anyone signs anything. Call 310.880.9718 for a free consultation.
Rates and programs change frequently; figures reflect October 2026 data. This page is general information, not financial advice — talk to a licensed lender about your specific situation.