If you are 55 or older and own a home in Contra Costa or Alameda County, California Proposition 19 lets you sell and buy again without losing your low property tax base. For long-time owners in Danville, Alamo and San Ramon (Contra Costa County) and Dublin (Alameda County), that can be worth thousands of dollars a year. It also works across county lines, so a move from Danville to Dublin qualifies.
Here is the problem it solves. Under Prop 13, your home's taxable value has grown no more than 2% a year since you bought it, while market values rose much faster. Normally, buying a new home resets your taxable value to the full purchase price. Prop 19, in effect since April 1, 2021, lets eligible homeowners take most of their old tax base with them instead.
This guide explains who qualifies, walks through the math with real-number examples, and shows how to file in Contra Costa and Alameda counties. Every situation is different, so we strongly recommend reviewing your plans with a qualified tax professional before you list.
Who qualifies for a Prop 19 base year value transfer
You can transfer your property tax base under Prop 19 if you meet these conditions:
You are 55 or older (or severely disabled, or your home was lost to a wildfire or natural disaster) on the date you sell your original home.
Both homes are your primary residence. You must have owned and lived in the home you sell, and you must live in the new one and qualify for the homeowners' exemption when you file.
You buy or build within two years of selling. The purchase can happen before or after the sale.
The new home can be anywhere in California, at any price. You are no longer limited to the same county.
You can use it up to three times in your lifetime.
If the new home costs more than the one you sold, you still benefit. The difference in value is simply added to the tax base you bring with you. Timing and valuation details can affect how your county calculates this, which is one more reason to confirm your numbers with a tax professional and the Assessor's Office.
How Prop 19 works: a step-by-step example
In this example, a 55+ homeowner saves about $11,570 a year in property tax by using Prop 19. Here is how the math works, step by step.
The situation. A homeowner bought a home in Danville (Contra Costa County) in 2010 for $900,000. Today it would sell for $2,200,000. They want to move up to a $2,800,000 home in Dublin (Alameda County).
Step 1: Find your tax base today
Under Prop 13, your taxable value starts at your purchase price and can rise no more than 2% a year.
Purchase price in 2010: $900,000
Grown at 2% a year for 16 years: × 1.37
Tax base today: about $1,235,500, even though the home would sell for $2,200,000
Step 2: Carry it to the new home
Prop 19 moves that tax base to the new home. Because the new home costs more, the difference is added.
Tax base you bring: $1,235,500
Plus the difference ($2,800,000 − $2,200,000): $600,000
New home's tax base: about $1,835,500, instead of the full $2,800,000
Step 3: Compare the tax bills
We use about 1.2% of the tax base as the yearly property tax rate. Actual rates differ between Contra Costa and Alameda counties and by tax rate area within each, so check the tax bill for the specific property.
Because Prop 13 lets the tax base rise only 2% a year, that gap compounds. Over 30 years, this example adds up to roughly $470,000 in property tax savings.
More Prop 19 examples: moving up and downsizing
The savings depend on one thing: how far your home's market value has pulled ahead of its tax base. The longer you have owned and the more your home has gained, the more Prop 19 is worth.
A few things stand out:
Downsizing keeps your whole tax base. When the new home costs less than the one you sold, nothing is added. In the downsizing example, the owner pays about $14,830 a year instead of $21,600.
A big gain matters more than a long hold. The 2000 buyer has owned longer, but their home gained less relative to its tax base, so their savings are smaller.
These are estimates. Prop 13 increases are capped at 2% but can be lower in some years, so your real tax base may be lower than our math assumes. Your tax bill shows your actual assessed value.
How to file for Prop 19 in Contra Costa or Alameda County
Prop 19 is not automatic. You file the claim with the Assessor in the county where your new home is located, not the one you sold. Buy in Danville, Alamo or San Ramon and you file with the Contra Costa County Assessor's Office. Buy in Dublin or Pleasanton and you file with the Alameda County Assessor's Office.
Sell and buy within two years. Either can come first.
Move in and file for the homeowners' exemption on the new home.
File Form BOE-19-B, the claim for a base year value transfer for homeowners 55 and older, with the Assessor.
File within three years of buying the new home to get full relief back to the purchase date. A later claim can still lower future tax bills.
Keep your records: both closing statements, proof of age, and your old home's tax bill showing its assessed value.
Ask your escrow officer and tax professional to help you line up the dates. A sale or purchase that lands outside the two-year window can cost you the benefit entirely.
Talk to a tax professional before you list
Prop 19 only changes your property tax. Selling a long-held home touches several other parts of your finances, and the right order of steps can save you far more than the transfer itself. Before you sign a listing agreement, sit down with a CPA or tax attorney to review:
Capital gains tax on the sale. Married couples can generally exclude up to $500,000 of gain on a primary residence ($250,000 for single filers). Gains above that can owe federal and California tax.
Timing. Which tax year the sale lands in, and whether to buy before or after you sell, can change both your income tax and your Prop 19 eligibility.
How title is held. Trusts, LLCs, co-owners and spouses can all affect who qualifies and how the claim is filed.
Your property tax deduction. Federal limits on deducting state and local taxes change how much a lower tax bill is worth to you.
Your estate plan. Prop 19 also changed how homes pass from parents to children, which matters if you plan to keep the home in the family.
We are real estate agents, not tax advisors. We can help you price your home, find the next one and time both moves. Your tax professional should confirm the numbers and your eligibility before you act.
Prop 19 FAQ for Contra Costa and Alameda County homeowners
What is Prop 19 in California?
Prop 19 is a 2020 California law that lets homeowners 55 and older, severely disabled homeowners and disaster victims move their property tax base to a new primary residence. It took effect for sales and purchases on or after April 1, 2021.
Can I use Prop 19 if my new home costs more?
Yes. If the new home costs more than the one you sold, the difference is added to the tax base you bring. You still pay far less than a full reassessment in most cases.
Can I move from Contra Costa County to Alameda County?
Yes. Prop 19 allows transfers anywhere in California, so you can sell in Danville and buy in Dublin, or the other way around. You file with the Assessor in the county where the new home is, so a Danville-to-Dublin move is filed with Alameda County.
How many times can I use Prop 19?
Up to three times in your lifetime, if you qualify each time.
How long do I have to buy the new home?
You must buy or build the new home within two years of selling the original home, either before or after the sale.
What form do I file?
Homeowners 55 and older file Form BOE-19-B with the county Assessor where the new home is located. File within three years of the purchase for full relief.
Does Prop 19 lower my capital gains tax?
No. Prop 19 affects property tax only. Capital gains, income tax and estate questions should go to a qualified tax professional.
See what Prop 19 could save you
Thinking about selling in Danville, Alamo, San Ramon or Dublin? Text us at 925.922.4482 with your address and the price range you're shopping in, and we'll run the numbers for you. Then take them to your tax professional before you decide.
Manjra Mian Group · Realty ONE Group FUTURE, DRE #01522885 · Tasneem Manjra, DRE #01802625 · Yasmene Mian, DRE #01461684
This article is for general information only and is not tax, legal or financial advice. Examples are illustrative, use an estimated 1.2% property tax rate and assume the full 2% annual Prop 13 increase. Eligibility and actual savings depend on your situation. Consult a qualified tax professional and confirm with the Contra Costa or Alameda County Assessor's Office before acting.
