What a Prop 8 review is
California's Proposition 13 sets a base value for your home when you buy it, and lets it grow no more than 2% a year. That grown-up number is your Prop 13 value.
Proposition 8, in the words of the State Board of Equalization, allows “temporary reductions in assessed value in cases where real property suffers a decline in value.” The County's form puts it this way: state law “authorizes the Assessor to temporarily lower the assessed value of any real property when it is greater than the market value as of January 1, lien date.” The request you file is the Assessor's Request for Value Review (Prop 8).
Three things to know, from the State Board of Equalization:
- It's temporary. “The decline in value is typically temporary.”
- It's reviewed every year. “Once a property's assessment has been reduced under Proposition 8, the Assessor reviews the assessment annually.”
- It never goes above your Prop 13 value. Unless the home sells or is built on, its “assessed value can never increase above its existing factored base year value.”
Who it helps
The question is whether your home's market value on January 1, 2026 was below the value the County has on the roll. The Board of Equalization's example: “if you purchase your property before a time when the real estate market falls dramatically, your property will likely benefit.”
That is most likely to be true if:
You bought in 2022, 2023 or 2024
Your Prop 13 value started at your purchase price, near the top of the market. Homes like yours may have sold for less around January 1, 2026.
Nearby sales came in below your roll value
Similar homes near yours sold for less than the County's number, close to January 1, 2026. The form has room for three.
You own a condo or a newer build
Compare with sales in your own complex or tract, not the houses around it.
Something hurts value the County can't see
The Board of Equalization says a decline “may result from changes in the real estate market, the neighborhood, or the property itself.”
Who it usually doesn't help: anyone who has owned since the 2010s or earlier. Your Prop 13 value has grown 2% a year from an old purchase price, and today's market value is almost certainly above it: a home “will not benefit from a lower assessment unless its market value falls below its current factored base year value.”
Check your numbers
Two numbers decide whether you have a case.
1. The County's value
Your 2026-27 tax bill shows it; the Treasurer-Tax Collector says annual bills “are mailed once a year in late September through early October.” You can also look it up on the Assessor's ParcelQuest property search. Your Assessor's Parcel Number (APN) is on the bill.
2. What similar homes sold for
The form asks for up to three comparable sales, each with its address or APN, sale date, price, square feet and a short description (“Single or Multi-family: # bedrooms & baths, # of units if multi-family, proximity”). The sale date “Must be prior to 3-31-26.”
If your sales come in meaningfully below the County's value, you have something to file. If they come in around it or above, you probably don't.
Your opinion of value
The form has one box that matters most: “Your opinion of value as of January 1, 2026.” That is the number you are asking the Assessor to use. Make it the number your sales support, not a wish.
You sign the form under penalty of perjury, declaring that its statements “are true, correct, and complete to the best of my knowledge and belief.”
If Jasmine Lane prepares your Package, the figure we give you is an opinion of value built from recorded sales of nearby homes. You decide whether to adopt it as your own before you sign.
How that figure is built, and why it is the higher of two readings, is documented at jasminelane.app/methodology/california.
How to file — free, yourself
The County calls it a “FREE Informal Value Review.” There is no online form: download the Request for Value Review (PDF), fill it in, sign it, and return it to the Assessor's Office.
The County's date, in its words. The form asks you to “return this request to the Assessor’s Office by November 30, 2026.” It also says: “Please attach any additional information pertaining to this request.”
Contact information
Your name, mailing address, daytime phone and email.
Property information
The APN, the property address, and your opinion of value as of January 1, 2026.
Up to three sales
Rows A to C: address or APN, sale date (before 3-31-26), price, square feet, description.
Sign and date
Under penalty of perjury, as the form states.
Fax or mail it, keep a copy
Keep the fax confirmation or a copy of what you mailed, with the date.
After you file
The Assessor reviews your request. Keep paying your bill. The form: “Any tax bills you’ve received must be paid. If this review results in a change in your assessed value, your taxes will be adjusted to reflect the difference.”
Questions: the Assessor's Office at (925) 313-7400, as the form says.
The review can't push you above your Prop 13 value.
If your home is taxed at its Prop 13 value, as most filers' are, the outcome is a lower number or no change.
The Appeals Board is a separate process
The County's form describes it this way:
- “The Assessment Appeals Board (AAB) is an independent body established to resolve differences of opinion between the Assessor and property owners as to property value.”
- “To have your issue heard before the board you must file a timely Application for Changed Assessment. These forms are available through and must be filed with the Clerk of the Board of Supervisors Office.”
- “The annual filing period for an Assessment Appeal is from July 2 through November 30, annually.”
The Clerk of the Board: Assessment Appeals or (925) 655-2008. Jasmine Lane does not prepare Appeals Board applications and does not appear before the Board.
While you're there — the Homeowners' Exemption
If you own and occupy the home as your principal place of residence, the Homeowners' Exemption takes $7,000 off its taxable value every year, which the County says “will reduce the annual property tax bill by at least $70 each year.” After you buy, the Assessor mails you the application “within several months.”
Our Homeowners' Exemption guide covers who qualifies, the dates, and how to claim it in Contra Costa County.
What Jasmine Lane does, and what it doesn't
Our Decline-in-Value Evidence Package is for owners who want the numbers done. In Contra Costa, where the form goes by fax or mail, we also send it:
- We prepare; you sign; we fax. We fill in the County's own form with the sales we relied on and an opinion of value. You check it and sign it on our site, along with a written authorization for us to fax it. We fax the form, a copy of your authorization (California law requires it), and the supporting pages to the Assessor.
- The Assessor talks to you, not us. Your name, phone and email go on the form. We don't sign for you and don't discuss your home's value with the Assessor or the Appeals Board.
- $149, due only after the fax goes through. Nothing is charged, held, or invoiced before then, and nothing is owed if you decide not to file.
- Refunded if you don’t save more than $149. Savings are the Assessor’s reduction times your tax rate. In full, decided by June 30, 2027. This is a promise about our fee, not about what the Assessor will decide.
The full terms are the Service Agreement (California). Enter your address below and the site shows the County's value for your home and what nearby sales say, before anything else.