California property tax terms, in plain English

The value the county uses to calculate your property tax bill. In California, the assessor enrolls the lower of two numbers every January 1: your factored base year value (the Prop 13 number) or your home's market value on that date (the Prop 8 number). Your bill is roughly 1.1–1.25% of this value. When you appeal, this is the number you're trying to lower. How the two numbers work together →

What your home would sell for in a normal, arms-length sale between a willing buyer and a willing seller — defined in Revenue & Taxation Code § 110. For property tax purposes, the only market value that matters is the value on January 1, the lien date. Not what Zillow says today, not what you paid, not what you owe on the mortgage.

The value the assessor enrolls when you buy a home or complete new construction — usually your purchase price. It's the starting line for everything Proposition 13 does, and it only resets when the property changes hands or you build something new.

Your base year value, grown by an inflation factor of at most 2% per year since you bought. This is the Prop 13 ceiling: your assessed value can never go above it, no matter how hot the market gets. It appears on your annual assessment notice, sometimes labeled the “Prop 13 value.” Prop 13 vs. Prop 8, explained →

The annual adjustment applied to your base year value — the change in the California Consumer Price Index from October to October, capped at 2%. The State Board of Equalization publishes the official factor every year. Most years it's the full 2%; in low-inflation years (2010 was 0.753%) it's less.

Your actual all-in property tax rate once voter-approved bonds and special assessments are added to Prop 13's 1% base rate. In most California counties it lands between roughly 1.05% and 1.25% of assessed value — which is why a $20,000 reduction in assessed value saves about $220–$250 a year, not $200.

The 1978 law that caps your basic property tax rate at 1% of assessed value and limits assessed-value growth to at most 2% a year for as long as you own the home. It's why two identical houses on the same street can have wildly different tax bills — the neighbor who bought in 1995 has a much lower base year value. Prop 13 vs. Prop 8 →

Prop 13's lesser-known counterpart, passed by voters the same year. It requires the assessor to temporarily lower your assessed value when your home's market value on January 1 falls below your factored base year value. This is the law most California residential property tax appeals run on. The full Prop 8 explainer →

The official name for a Prop 8 reduction — the procedure in Revenue & Taxation Code § 51(a)(2) where the assessor enrolls your lower market value instead of your factored base year value. County websites use “decline-in-value,” “DIV,” “DV,” and “Prop 8” interchangeably; they all mean the same thing. How decline-in-value reassessment works →

January 1 — the single date each year when your property's value is fixed for the next tax bill. Everything in an appeal is about proving what your home was worth on this date. A market drop in June doesn't help your current bill; it matters on the following January 1. Every deadline that follows from the lien date →

The elected county official whose office sets assessed values for every property in the county. Informal review requests go to the Assessor's office. Formal appeals go to a separate body — the Assessment Appeals Board — because what you're disputing is the Assessor's number.

The unique ID the county assigns to your property. It's printed on your tax bill and assessment notice, and every appeal form asks for it. If you can't find it, your county assessor's website can look it up by address.

The letter many counties mail each summer showing the value they've enrolled for your property. It matters twice: it's your early warning that you might be overassessed, and in counties that mail notices to all homeowners, it sets the formal appeal deadline at September 15 instead of November 30. Deadlines by county →

A free request asking the Assessor's office to lower your assessed value. A county appraiser reviews your comparable sales evidence — no hearing, no filing fee, and the Assessor cannot raise your value through this process. Every county Overassessed serves offers one, each with its own form and filing window.

The official appeal filed with your county's Assessment Appeals Board on form BOE-305-AH, with a filing fee in most counties ($0–$50 depending on the county). Unlike the informal review, it preserves your legal appeal rights and ends in a binding decision — but the board can also raise your value if the evidence supports it. What evidence wins a formal appeal →

An independent county panel — not part of the Assessor's office — that hears formal appeals and decides your assessed value based on evidence from both sides. Its decision binds the Assessor. Based on the evidence presented, it can lower, confirm, or raise your assessment.

The county office that accepts and processes formal appeal applications and schedules hearings. When a deadline says an application must be “filed with the Clerk,” this is who it means — not the Assessor's office.

A written swap of evidence between you and the Assessor before a formal hearing, under Revenue & Taxation Code § 1606. Request it at least 20 days before your hearing and the Assessor must show you their valuation evidence — the cleanest way to see their case before you present yours.

Who has to prove the value. Normally the Assessor's value is presumed correct and the homeowner must prove it's wrong. But for an owner-occupied single-family home, the burden shifts to the Assessor — provided you supplied all the information the law requires. That's a real homeowner advantage most appeal services never mention.

The Assessment Appeals Board generally has two years from a timely, complete application to decide your case, under Revenue & Taxation Code § 1604. If it doesn't decide in time, your opinion of value generally becomes the assessed value until the board rules — with some conditions and waiver exceptions.

Recent arms-length sales of homes similar to yours in size, age, condition, and location. They're the core evidence in nearly every residential appeal: if three similar homes sold for less than your assessed value around January 1, that's your case. How to pick comps that hold up →

The dollar corrections that translate a comp's sale price into what it implies about your home — subtracting for the comp's extra bathroom, adding back for your bigger lot, correcting for price movement between the sale date and January 1. Required by Property Tax Rule 4. Appeals with documented adjustments are far more credible than raw sale prices.

An appeals board cannot consider sales that closed more than 90 days after the valuation date, under Revenue & Taxation Code § 402.5. For a regular Prop 8 appeal, that means no sales after roughly March 31 of the appeal year. There's no limit looking backward in time — only forward. The 90-day rule in practice →

A computer estimate of your home's value — Zillow's Zestimate, Redfin's Estimate. Useful as a gut check, but not accepted as evidence by California assessors or appeals boards: AVMs aren't tied to the lien date and their methodology can't be examined. Use real closed sales instead.

An extra, one-time assessment (and bill) issued when you buy a home or finish new construction mid-year, covering the gap between the previous assessed value and yours. It has its own appeal clock — generally 60 days from the date on the supplemental notice or bill, depending on the county.

A back-dated assessment correcting a value the county set too low in an earlier year — value that “escaped” taxation. Like supplemental assessments, escape assessments carry their own appeal window, generally 60 days from the date on the notice.