Does an ADU Increase Property Taxes in California? San Jose Guide

Quick Answer: Yes, building an ADU in California increases your property taxes, but only on the ADU’s assessed value — not on your entire property. A $150,000 ADU adds approximately $1,800/year in property taxes (1.2% effective rate in Santa Clara County). This is offset by typical ADU rental income of $2,200–$4,500/month.

ADU and Property Taxes in California: What San Jose Homeowners Need to Know

One of the most frequently asked questions from San Jose homeowners considering an ADU is: “Will my property taxes go up?” The short answer is yes — but only on the new ADU’s value, not your entire property. Here’s the complete picture.

How California Property Tax Works (Proposition 13)

California’s Proposition 13 (1978) limits annual property tax increases to 2% per year, and properties are only reassessed to full market value when they’re sold or new construction occurs. This is great news for long-time homeowners: if you’ve owned your San Jose home for 20+ years, your existing home’s assessed value may be far below market value — and building an ADU doesn’t change that base assessment.

How ADU Construction is Taxed

When you build an ADU, the county assessor adds only the ADU’s assessed value to your property tax base. Your existing home’s assessed value remains unchanged. The ADU is assessed based on its construction cost (or market value if lower), not the value it adds to your overall property.

Example:

• Your existing home assessed value: $650,000 (from when you bought 15 years ago)
• New ADU construction cost: $150,000
• New total assessed value: $800,000
• New property tax (Santa Clara County ~1.2% effective rate): $9,600/year
• Previous property tax: $7,800/year
• Tax increase: $1,800/year

ADU Tax Increase vs Rental Income

A $1,800/year tax increase is easily offset by ADU rental income:

• ADU rental income (San Jose average): $2,500/month = $30,000/year gross
• Tax increase: $1,800/year
• Net rental income after tax increase: $28,200/year
• Monthly net: $2,350

Additional Tax Considerations

• Rental income is taxable: ADU rental income is ordinary income. You can offset it with depreciation ($150,000 ADU ÷ 27.5 years = $5,454/year depreciation deduction)
• Mortgage interest deduction: If you financed the ADU with a HELOC, interest may be deductible
• Property tax deduction: California property taxes are deductible up to $10,000 state+local combined (SALT cap)
• Capital gains at sale: ADU adds to your home’s tax basis, potentially reducing capital gains when you sell

Quartz Construction builds ADUs in San Jose. The financial case for ADUs is compelling despite the modest tax increase. Call (650) 749-7436. CSLB #1003436 | BBB A+ | 4.9⭐. Learn more about ADU construction.

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Quartz Construction & Remodeling | CSLB #1003436 | Licensed, Bonded & Insured

Phone: (650) 749-7436

Address: 1777 Hamilton Ave #1080, San Jose, CA 95125

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