I Just Bought My Home — Can I Appeal the Assessment?

New buyers usually assume their assessment is unarguable — they just paid the price it's based on. Sometimes that's right. But a purchase creates a base year value, and correcting a base year value is worth far more than a one-year reduction, because every future year is factored up from it.

What happens to your assessment when you buy

A change in ownership triggers reassessment to full cash value as of the transfer date, establishing a new base year value that then rises up to 2% a year under Prop 13. The assessor's usual starting point is your purchase price, on the reasonable theory that an open-market sale is the best evidence of market value.

You'll then get a supplemental assessment — a bill for the difference between the old and new value, prorated for the remainder of the fiscal year. This is the bill that surprises people who budgeted from the seller's tax history. (Why assessed and market value diverge.)

When the purchase price isn't market value

The purchase price is presumptive evidence, not conclusive. Grounds to argue your base year value should be lower than what you paid:

• It wasn't an arms-length transaction. Family sale, sale between related entities, a purchase from a lender, or any deal not exposed to the open market.
• You bought under duress or on a compressed timeline — a 1031 exchange deadline, a relocation, an estate that needed to close.
• The price included non-real-property items. Furniture, a boat slip, business assets, or a seller-financing structure with an above-market rate. Personal property isn't part of the real property assessment.
• The assessor enrolled something other than your price. They sometimes conclude the market value exceeded what you paid, and enroll the higher figure. That's directly appealable.
• The assessor's record is wrong. Wrong square footage, bedroom count, or condition carried into the new base year value.
• You bought at a market peak and closed after it turned. This one is a Prop 8 decline-in-value appeal for the following lien date rather than a base year challenge — see below.

Two clocks, and they're different

The supplemental assessment: 60 days. Appeal within 60 days of the mailing date on the supplemental notice (next business day if day 60 is a weekend or holiday). This window has nothing to do with the July–September/November period and can open any month of the year.

The base year value: up to four years. This is the part buyers miss. A base year value set at a change in ownership is conclusively presumed correct unless an application is timely filed within the first four years. You may appeal it during the regular filing period for the first year it's enrolled on the roll, or during the regular filing period for any of the next three years.

So if you bought in 2024 and only now realize the enrolled value was too high, you may still have a window — but confirm the specifics with your Clerk of the Board, because which years remain open depends on when the value was first enrolled. (Your county's regular filing period.)

Base year appeal vs. decline-in-value appeal

Don't confuse them; they're different boxes on the application and different arguments.

	Base year value appeal	Prop 8 decline-in-value
Argument	The value set at purchase was wrong	Market value has since fallen below assessed value
Valuation date	Date of transfer	January 1 lien date
If you win	Permanent — lowers the base all future years grow from	Temporary — reviewed annually, restored as market recovers
Window	First year enrolled + next 3 years	Each year's regular filing period

If you bought at the top of a cycle and values fell afterward, you likely want the Prop 8 route for the affected years, not a base year challenge. (What Prop 8 does.)

One caution specific to buyers

Appealing a base year value puts that figure under examination in both directions, and a board isn't bound by either side's number. If your assessor's record currently understates the property, look at it before you invite a closer look. (The realistic risks.)

Also file for the homeowners' exemption if you haven't — it's a separate reduction, and it's the qualifying condition for the presumption that shifts the burden of proof onto the assessor at a hearing.

What evidence to bring

The same currency as any other appeal: arms-length sales of comparable properties near the relevant valuation date, honestly compared on location, type, size, age, condition, and features. For a base year appeal, that means sales around your transfer date; for a Prop 8 appeal, sales near the January 1 lien date, with nothing dated more than 90 days after it (§402.5). Plus, if applicable, the documents showing why your own transaction wasn't a clean market sale. (Choosing comps that hold up.)

CompFinder assembles the comparable-sales side of that for San Francisco, Oakland, San Jose, Seattle, and Issaquah.