Does an ADU Increase Your Property Tax in California?
Updated June 12, 2026 · Upside ADU
Quick answer
Building an ADU does not trigger a full reassessment of your home. California uses a 'blended' approach: only the new ADU's added value is assessed and taxed, while your existing home keeps its Proposition 13 base. Expect roughly 1–1.25% of the ADU's construction value in added annual property tax.
How does ADU property tax work in California?
When you add an ADU, the county assessor values only the new construction and adds that figure to your assessment. Your main home's Proposition 13 base year value is not touched. This is called blended assessment: the old house keeps its protected, lower assessed value, and only the ADU is taxed at current value. So an ADU that costs $250,000 to build typically adds roughly $2,500–$3,100 in annual property tax — not a reassessment of the whole property.
How do you estimate the added tax?
The added tax is roughly the ADU's assessed value times your local tax rate (about 1–1.25% in the Sacramento region, including voter-approved bonds). Assessed value usually tracks construction cost. Use the table to ballpark it, then confirm your exact rate on your county tax bill or with the Sacramento County Assessor.
Estimated annual property-tax increase by ADU value (2026)
| ADU added value | At 1.0% | At 1.25% |
|---|---|---|
| $100,000 | $1,000/yr | $1,250/yr |
| $150,000 | $1,500/yr | $1,875/yr |
| $250,000 | $2,500/yr | $3,125/yr |
| $400,000 | $4,000/yr | $5,000/yr |
See also:What an ADU costs in Sacramento — estimate the added value
Why isn't your main house reassessed?
Proposition 13 caps annual increases in a property's assessed value and only allows full reassessment on a change of ownership or new construction (see the California State Board of Equalization). Adding an ADU is new construction, but the assessor applies it narrowly — only the ADU is the 'new' value. The existing home is unchanged in the eyes of the assessor, so its long-held, lower base year value carries forward untouched.
Is there a special ADU property-tax break?
No — California has no ADU-specific property-tax exclusion. A proposed one (SB 1164) stalled in the Legislature in 2024 and never became law, so don't budget around it. Your only protection is the standard Proposition 13 treatment described above: the assessor adds the ADU's new value and leaves your main home's base year value untouched. Confirm current treatment with your county assessor before you build.
See also:California ADU law in 2026 — statewide ADU changes
How does property tax affect your ADU's return?
The added property tax is a real holding cost, so it belongs in any honest ROI calculation. On a unit renting for $2,000/month, a $2,800 annual tax bill consumes a little over one month of rent — meaningful but small against gross income. The full payback math, including taxes, insurance, and management, lives in the ROI guide.
What are the most common property-tax mistakes?
- Assuming the whole home gets reassessed — only the ADU's value is added
- Forgetting to budget the added tax into monthly cash flow
- Confusing assessed value with market value — assessed value tracks construction cost
- Overlooking local bond rates that push the effective rate above 1%
- Treating this guide as tax advice instead of confirming with the county assessor
This guide is general information, not legal or tax advice. ADU rules change often and vary by city — we confirm the current requirements for your jurisdiction during your free feasibility check.
Sources & references
- Property Taxes & Proposition 13 — California State Board of Equalization
- Property assessment & new construction — Sacramento County Assessor
- Accessory Dwelling Units — official guidance — California Dept. of Housing & Community Development (HCD)
External links open official government and lender resources. Construction price and rent figures reflect 2026 Sacramento-region market conditions; confirm current rules and fees with your jurisdiction.