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Understanding assessments

We assess property to help calculate fair property taxes. Your assessed value is based on rules set by Proposition 13, passed by CA voters in 1978.

Assessed Value and Proposition 13

Marin County Civic Center

Proposition 13 added Article XIII A to the California Constitution. It changed how property taxes are calculated.

Here’s what it did:

  • Limited the general property tax rate to 1% of the assessed value (plus any voter-approved local bonds)
  • Made it harder for governments to add new property taxes
  • Changed how and when property is reassessed

How we calculate your assessed value

Your assessed value starts with the market value of your property at the time you buy or inherit it. This is called your base year value.

Each year after that, the value:

  • Can increase by no more than 2%
  • Stays the same unless you make changes or sell the property

When your property gets reassessed

Your property may be reassessed if:

  • You sell, transfer, or inherit it
  • You build something new or remodel significantly

We do not reassess every year unless one of these changes happens. When reassessing, we may use:

  • Local real estate market trends
  • Sales of similar properties
  • Construction costs
  • Potential income the property could earn

Get more information

Received a notice? Check your current value? Estimate new taxes? Use the buttons below. Need help? Contact us at 415-473-7215 (CA Relay 711). We’re here to answer your questions.

Notices  Find my Assessed Value 

Frequently asked questions about assessed value for property tax purposes

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You can find your property’s assessed value on your property tax bill, which is mailed each year in late September or early October.

You will only get a separate notice if:

  • Your property was reassessed for a reason other than the standard 2% increase allowed under Proposition 13
  • You had a temporary reduction in value under Proposition 8, and that value has changed

If your value increased more than 2%, it may be because of Proposition 8.

Here’s how it works:

  • Proposition 13 limits increases to 2% per year on your base year value
  • But Proposition 8 allows for temporary reductions if your property’s market value drops
  • When market values go back up, the temporary reduction ends, and your assessed value can increase by more than 2%, but only up to your original base year value, adjusted for inflation
  • After that, the 2% limit applies again

If you think your assessed value is too high, you can:

  1. Request an informal review with the Assessor’s Office (between July 1 and October 31)
  2. File an appeal with the Assessment Appeals Board (between July 2 and November 30)

We’re here to help you understand the process.

Call us at 415-473-7215 (CA Relay 711). You can also schedule an appointment online. 

More about declines in value: informal reviews and formal appeals

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If your assessed value is higher than what you believe your property is worth, you may qualify for a temporary reduction in value under Proposition 8.

What you can do: 
Call us at 415-473-7215 (CA Relay 711) to discuss your concerns

  • Request an informal assessment review between July 1 and October 31
  • File a formal appeal with the Assessment Appeals Board between July 2 and November 30

An informal assessment review is a free appraisal by the Assessor’s Office. We compare your assessed value with your property’s market value as of January 1.

To qualify for a temporary reduction:

  • Your market value must be lower than your assessed (factored base year) value
  • This reduction is temporary and reviewed each year
  • If market value rises, your value may increase by more than 2% until it reaches your factored base year value

This rule comes from Proposition 8, passed in 1978, which allows for temporary tax relief when property values drop.

Example 1:
You bought a home in 2023 for $1,500,000. On January 1 this year, its market value is $1,350,000.
✅ You may qualify for a temporary reduction because the market value is lower than your base year value.

Example 2:
You bought a home in 2010 for $500,000. The assessed value is now $627,995, but the market value is $975,000.
❌ No reduction applies because the market value is higher than your assessed value.

  • Forms are available each year starting July 1
  • You can get a form:
    • Online
    • By calling 415-473-7215
    • At our office: Marin County Civic Center, Suite 208
  • The deadline to submit the form is October 31
  • You can include your opinion of value and any recent comparable sales

If you disagree with the value on your tax bill or notice, and want a formal hearing, you can:

  • File an Assessment Appeal Application with the Clerk of the Assessment Appeals Board
  • The filing period is July 2 to November 30
  • There is a $50 fee
  • Late applications are not accepted

For more information, call 415-473-7345 (CA Relay 711) or visit the  Assessment Appeals Board page.

The examples below illustrate scenarios in a changing real estate market. Although a decline in value reduction (Proposition 8) may be appropriate in the top example, it is not applicable in the bottom example.

The graph below illustrates the assessable value being lowered to correspond to a lower market value in years 3, 4, and returning to the factored value at year 5. 

 

Line graph showing a reduction in market and assessed values as described in text.

The graph below illustrates the market value did not drop below the assessed value; therefore, a reduction is not warranted. 

Line graph showing the assessed and factored values slowly increasing and remaining below the market value.

  • July 1 to October 31 – Informal assessment review filing period
  • July 2 to November 30 – Formal appeal application filing period

We’re here to answer your questions and help you navigate the process.

  • Call 415-473-7215 (CA Relay 711)
  • Visit our online calendar to make an appointment

Related

Page updated June 4, 2025

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