Decline-in-Value Reassessment in California: What It Is and How to Get One
The official name for a Prop 8 reduction. Here's how California's lien date, factored base year value, and county processes actually work.
A decline-in-value reassessment — sometimes called a DV or DIV — is what happens when the California assessor temporarily lowers your assessed value because the market value of your home on January 1 is below the Prop 13 ceiling. The official name comes from Revenue & Taxation Code § 51(a)(2). Most homeowners know it as “Prop 8.” They're the same thing — Prop 8 is the constitutional authority, and decline-in-value reassessment is the actual procedure the assessor follows.
This page explains what gets compared, why January 1 is the only date that matters, what the assessor does on its own versus what you have to request, and how the reduction reverses when the market recovers.
What is a “decline-in-value reassessment”?
It's a temporary downward adjustment to your assessed value, made by the county assessor when your factored base year value (FBYV) is higher than your property's market value as of January 1. R&T § 51(a) tells the assessor to enroll, every year on the lien date, the lower of those two numbers.
It's temporary
Each January 1 the assessor re-checks. If the market has moved back up, your assessed value moves up with it (capped at the Prop 13 ceiling).
It does not reset your Prop 13 base year
Your factored base year value continues to grow in the background by the regular up-to-2%-a-year inflation factor, even while you enjoy a lower assessment.
It applies only as of the January 1 lien date
The assessor cannot give you a decline-in-value reduction based on what your home is worth in May or August — only what it was worth on January 1.
Is decline-in-value the same as Prop 8?
Yes, in plain English. Prop 8 is the constitutional authority — voters in 1978 amended Article XIII A § 2(b) to allow the value to be “reduced to reflect substantial damage, destruction, or other factors causing a decline in value.” R&T § 51 is the statute that implements that authority. The actual annual procedure each assessor follows — comparing factored base year value to market value, and enrolling the lower one — is what gets called a “decline-in-value reassessment.” Most assessor websites use both terms interchangeably (Santa Clara, Alameda, Orange, and San Mateo all do).
For the deeper Prop 8 explainer, see what is Proposition 8. For how Prop 8 fits with Prop 13, see Prop 13 vs. Prop 8.
Why is January 1 — the lien date — so important?
Because it's the only date the assessor is allowed to consider. R&T § 51(a) anchors the entire annual valuation to the lien date, which has been January 1 since 1997 (it was March 1 before that).
This matters in three concrete ways:
- Your comparable sales need to be near January 1. Under R&T § 402.5, an appeals board cannot consider sales that closed more than 90 days after the lien date. For most homeowners, this means sales must have closed by approximately March 31.
- A mid-year market crash doesn't automatically help your current bill. If the market is fine on January 1 but tanks in June, you don't get a decline-in-value reduction for that fiscal year. You'd have to wait until the next lien date.
- A mid-year recovery doesn't reverse a reduction in the same year. Once the assessor enrolls a value as of January 1, that's the value on your bill for the entire fiscal year (July 1 – June 30).
The “lien date” is also why every decline-in-value request form has a specific year on it — the form for the 2026-27 roll is locked to the January 1, 2026 valuation date.
What is “factored base year value” and what gets compared?
Your factored base year value (FBYV) is your purchase price (or the value when you completed new construction), grown each year by an inflation factor of up to 2%. The State Board of Equalization publishes the official inflation factor every year as a Letter to Assessors.
On every January 1, the assessor compares two numbers:
- Your factored base year value (the Prop 13 number)
- The full cash value (market value) of your home on that date, as defined in R&T § 110
The assessor enrolls the lower one. If your FBYV is $815,000 and a competent appraisal of your house on January 1 says it would sell for $760,000, the assessor enrolls $760,000 as a decline-in-value assessment.
A common misconception
“Market value” in this context is the price your home would sell for on January 1 under typical market conditions — not what you paid for it, not what you owe on the mortgage, not what Zillow says today.
How does the assessor's office actually do this?
This varies a lot by county — see your county's page on Overassessed for specifics. The general framework looks like this:
What the assessor reviews on its own
Most California assessors proactively run automated reviews of properties they suspect might qualify, especially properties already in DIV status from a prior year. Alameda County has explicitly committed to this proactive approach for years — its Assessor's Office reviews all properties that received a reduction the prior year, plus any others that might warrant a decrease. Santa Clara proactively reduced more than 17,000 properties in 2023, totaling roughly $4.7 billion in assessed-value reductions, before any homeowner had to file.
R&T § 51(e) explicitly prohibits the assessor from conditioning that annual review on the homeowner filing an appeal: “In no event shall the assessor condition the implementation of the preceding sentence in any year upon the filing of an assessment appeal.”
What you can request
If the assessor's automated review didn't catch your property — or did, but enrolled a value you think is still too high — you can submit an informal decline-in-value request to the assessor's office. Every county has its own form (for example, LA County's Form RP-87, Alameda's Informal Request for Decline in Market Value Reassessment, Santa Clara's online DIV request). The forms are short, free, and don't require a hearing.
You provide your opinion of value, comparable sales as of January 1, and any condition documentation. A certified appraiser at the assessor's office reviews and either lowers your value, leaves it unchanged, or — rarely — raises it.
How county processes differ
Each county runs its own informal-review window and uses its own form. Filing windows and assessor practices vary widely. For the specific deadline and form in your county, see California property tax deadlines by county. For Alameda specifically, see how to appeal in Alameda County.
How is a DIV reduction reversed when values recover?
Each January 1 lien date, the assessor re-checks the market. If your home's January 1 market value is now higher than before but still below your Prop 13 ceiling, the assessor enrolls the new (higher) market value. The 2% Prop 13 cap does not apply during this period, because Prop 8 — not Prop 13 — is governing your assessment. So your assessed value can rise more than 2% in a single year.
There's still one ceiling: your assessed value cannot exceed your factored base year value. Once market value catches back up to the FBYV, you're returned to the regular Prop 13 track and the 2% cap reapplies the next year.
Worked example (illustrative)
- 2018 base-year value: $700,000
- 2021 factored base year value: $742,846
- 2021 market value (Prop 8 enrolled): $710,000 — you save tax on $32,846 of value
- 2022 market value: $695,000 — you save tax on more
- 2023 market value: $740,000 — assessed value jumps from $695,000 to $740,000, a 6.5% increase, because Prop 8 governs and the 2% cap doesn't apply
- 2024 market value: $810,000 — you've now caught back up; the assessor enrolls the factored base year value of $788,314 because that's lower
How do I know if I'm currently in DIV status?
Look at your county's annual Notice of Assessed Value, mailed in June or July depending on the county. Most counties show your factored base year value separately from your “current assessed value” or label your status with something like “Proposition 8 (Decline in Value)” or “Economic Adjustment (ECA).” If the two numbers differ and the lower one is enrolled, you're in DIV status.
You can also call your county assessor's office. Every California county is required to be able to look up both your FBYV and your current assessed value and tell you whether you're under a Prop 8 reduction.
Can I get a decline-in-value reduction for a prior year?
No. Counties are explicit on this — BOE Publication 800-10 and every county assessor that publishes guidance say the same thing: only the current January 1 assessment can be reviewed under decline-in-value. If you missed the window for a prior year, that year is closed for informal review. (A formal assessment appeal has different rules and a separate deadline — see California property tax deadlines.)
The reason is that R&T § 51(a)(2) anchors the value to “the lien date.” Once the roll for that year is closed, the assessor's authority to look at that lien date is exhausted.
Frequently asked questions
Sometimes. Counties run automated reviews each spring, and many properties get reductions without the homeowner doing anything — Alameda has run a proactive review program for over a decade, and Santa Clara reduced more than 17,000 properties in 2023 without homeowners filing. But automated reviews don't catch every property that qualifies. If you think yours was missed, file the informal review request with your county assessor.
No. R&T § 51(e) requires the assessor to annually re-review every property already in DIV status until the factored base year value is again the lower number. You don't refile.
Yes — and this surprises a lot of homeowners. While you're in Prop 8 status, the 2% cap doesn't apply. The assessor enrolls actual market value each January 1. If the market jumps, your assessed value can jump too — but never above your factored base year value for that year.
No. Decline-in-value relief is specific to the January 1 fair market value and does not allow for relief pertaining to other dates, including the supplemental assessment date triggered by a sale or completed construction. To dispute a supplemental assessment, you have 60 days from the date on the supplemental notice to file a formal appeal — a different procedure with a different deadline.
Only if you waited too long. The informal review timeline does not extend the formal appeal deadline. Most counties — Alameda, San Mateo, Santa Clara, San Diego, and Orange — explicitly recommend filing the formal assessment appeal (BOE-305-AH) before the formal deadline as a backstop, even if your informal review is still pending. If you withdraw later because the informal review came out in your favor, you can do that.
Yes — Prop 8 applies to all real property, not just owner-occupied homes. The mechanics are the same, but the evidence is usually different (income approach using rent rolls, vacancy data, and capitalization rates rather than residential comp sales).
What to do next
If you think you might be over-assessed and want to start with the informal route, find your county's decline-in-value request form on your county assessor's website (Overassessed has a county-by-county breakdown linked from the bottom of every page). If you've already missed the informal window or your informal request was denied, the next step is a formal appeal on BOE-305-AH — see what evidence wins and California property tax deadlines.
Overassessed is operated by a homeowner advocate, not a CPA or attorney. Everything on this page traces back to the California Constitution, the Revenue & Taxation Code, the State Board of Equalization, and individual county assessor publications.
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Overassessed provides estimates based on publicly available data and AI-generated analysis. This is not a formal appraisal, legal advice, or tax advice. Results are not guaranteed, and appeal outcomes depend on county review. Users file their own appeals. AI-generated estimates may differ from actual market values.