Alameda County Assessor's August Newsletter - Understanding Assessed Value, Supplemental Assessments & Livermore's Historic Wineries

Dear Alameda County Residents,

August is upon us and I'm sure many of you are starting to gear up for the back-to-school season. As we transition into this busy time, I hope you find everything you need to get your families ready for a successful school year!

You received your 2025 - 2026 Assessment Notice in the mail by now. If you disagree with your assessment, you can appeal your assessment. For more information, you can check out our website or you can reach out to our office.

On July 19th, Assessor staff joined the 15th annual Castro Valley Pride Celebration at Castro Valley High School where we met with our constituents. Thank you to all the organizers and attendees!

As always, we remain committed to serving the residents of Alameda County.

Sincerely,

Phong La

Alameda County Assessor

Understanding Assessed Value & Supplemental Assessments

Understanding how your property is valued can help you avoid surprises — like unexpected tax bills — and even save money. Here's a quick guide to help you navigate your property taxes in Alameda County.

What Is Assessed Value?

All taxable property in Alameda County is assigned an assessed value by the Assessor's Office. This value is used to calculate your property taxes and may not match current market value.

Here's how it works:

If you bought your home at market price, your assessed value is likely your purchase price.
If you paid below market price, your assessed value may be adjusted to match fair market value, based on recent sales of similar homes in your area.

Proposition 13, passed in 1978, protects homeowners by limiting how much your assessed value can increase each year—no more than 2%, unless there's new construction or a change in ownership.

What Is a Supplemental Assessment?

After you buy a property, the Assessor's Office will update the value to reflect market value as of your purchase date—even if your regular tax bill is still based on the old value.

This triggers a Supplemental Assessment, which may result in a separate tax bill for the increased value.

Key Points:

Only the difference in value is taxed in the supplemental tax bill
The supplemental tax bill is prorated from the date of purchase to the end of the fiscal year
You'll get a "Notice of Supplemental Assessment" by mail
Supplemental tax bills are in addition to your annual property tax bill

For FAQs and more details, visit the Assessor's Supplemental Assessment page HERE.

Can You Reduce Your Property Taxes?

You may qualify for exemptions or request a review or appeal of your assessed value.

Common Exemptions:

Homeowner's Exemption – If your home is your primary residence
Veterans' Exemption – For qualified military veterans

To appeal your property's value:

Informal review: Contact the Assessor's Office
Formal appeal: File with the Assessment Appeals Board between July 2 and September 15

Find info on exemptions and appeals on the Assessor's website HERE.

Looking Up Your Property Tax Info

To check your current tax balance or make a payment online, visit the Alameda County Treasurer-Tax Collector's website HERE.

Prefer in-person? Visit: County Administration Building 1221 Oak Street, Room 245, Oakland, CA, Or call: (510) 272-3787.

Why Can't You Find Owner Names on the Assessor's Website?

Due to the privacy laws which apply to government agencies—owner names are not published online, even though property records are public documents.

Disclaimer: This newsletter provides general information only. For legal or financial advice, please consult an attorney or CPA.

Alameda County Historic Spotlight

Livermore's Historic Vineyards

Livermore Valley is one of California's oldest wine regions, with a viticultural legacy dating back to 1849 when Robert Livermore planted the area's first vineyard. Originally home to the Ohlone Indians and later part of a Spanish land grant, the valley grew into a vital stop during the Gold Rush and was officially established as a town in 1869. In the late 1800s, wine pioneers like Charles Wetmore, James Concannon, and Carl Wente transformed the region—Wetmore's Cresta Blanca Winery earned international acclaim by winning the Grand Prix at the 1889 Paris Exposition, Concannon produced sacramental wine to survive Prohibition, and Wente founded what is now the oldest continuously operated family winery in the U.S.

By 1900, the valley boasted 50 wineries, but Prohibition devastated the industry. It wasn't until the 1930s that Livermore began to recover, becoming the first U.S. wine region to label and market varietal wines. A winery boom in the 1970s was followed by urban encroachment, which led to a dramatic decline by the late 1980s. In response, local governments implemented the South Livermore Valley plan to preserve agricultural land and support winery growth. Today, visitors can explore over 50 wineries in a region rich with history, fertile gravelly soil, and a Mediterranean climate, where welcoming vintners offer tastings, events, and a true connection to California's winemaking roots.