Most Californians know Proposition 13 caps annual increases in assessed value at 2%. Far fewer know about its companion, Proposition 8, passed the same year in 1978, which requires the assessor to temporarily lower your assessment when your property's market value drops below its Prop 13 value. If your home's value has fallen, Prop 8 is how you get relief.
How Prop 8 works
Each year the assessor must enroll the lower of two numbers: your Prop 13 factored base-year value, or your property's market value as of the January 1 lien date. When the market falls below your Prop 13 value, Prop 8 requires the assessor to use the lower market value — reducing your taxable value and your bill for that year.
The catch: it's temporary and can rise again
A Prop 8 reduction is not permanent. Once your property is in Prop 8 status, the assessor reviews its value every year. As the market recovers, your assessed value can increase by more than the usual 2% Prop 13 cap — all the way back up to your factored base-year value. Prop 8 gives real relief in a down market, but it is not a permanent cap reduction.
How to request a review
- Start informally: many county assessors accept a decline-in-value review request (an online form or letter) and will re-examine your value without a formal appeal.
- If the informal request is denied or the deadline is near, file a formal Application for Changed Assessment (Form BOE-305-AH) with your county Assessment Appeals Board.
- File the formal application during your county's regular appeal window — generally July 2 through September 15 or November 30, depending on the county.
Evidence that wins a Prop 8 case
- Comparable sales close to the January 1 lien date — Prop 8 is judged as of that date, so sales from later in the year carry less weight.
- Two to four sales of similar nearby homes that sold below your current assessed value.
- Documentation of condition problems that reduce your market value.
Check whether your county assessor offers a proactive decline-in-value form first — it is faster and free. Keep the formal Assessment Appeals Board deadline (Sept 15 or Nov 30) as your backstop so you don't lose the year.
Sources & currency: Proposition 8 decline-in-value rules, the January 1 lien date, and the BOE-305-AH appeal process were verified against the California State Board of Equalization and county assessor practice as of July 2026 (Revenue & Taxation Code section 51). County filing windows differ (Sept 15 vs Nov 30) — confirm yours.