A Tax on What You Paid, Not What It's Worth
In most states, your property tax is based on your home's current market value. California threw that model out in 1978. Under Proposition 13, your tax is based on what you paid for the home, adjusted upward by at most 2% per year, no matter what the market does. Two identical houses on the same street can carry bills that differ by a factor of five, depending only on when each owner bought.
Understanding this system, and the 2020 update known as Prop 19, is worth real money whether you're buying your first California home, turning 55, or inheriting a family house.
How Prop 13 Works
Proposition 13 has three moving parts:
- The 1% cap. The base property tax rate is limited to 1% of assessed value. Voter-approved bonds and special assessments get added on top, so real-world total rates typically land between 1.1% and 1.3% of assessed value depending on the city and school district.
- The 2% cap. Your assessed value starts at your purchase price (the "base year value") and can grow by at most 2% per year, tied to inflation. In practice, inflation has exceeded 2% in almost every recent year, so the full 2% applies.
- Reassessment on sale. The property is reassessed to full market value only when it changes ownership or when new construction is completed (and only the new construction is added at market value).
The math over time: buy a home for $500,000 and after ten years of 2% increases your assessed value is about $609,000, roughly $6,700–$7,900 a year in tax at typical total rates. If the home's market value doubled to $1,000,000 in that time, you're paying taxes on barely 60% of what it's worth. Your new neighbor who just paid $1,000,000 for the identical house next door starts at the full million. That's the famous "welcome, stranger" effect: the longer you've owned, the bigger your discount, and newcomers subsidize long-time owners.
The Supplemental Bill That Surprises New Buyers
When you buy, the county doesn't just adjust next year's bill. It issues a supplemental assessment covering the gap between the seller's old assessed value and your purchase price, prorated for the months remaining in the fiscal year (July 1–June 30). Buy between January and May and you'll receive two supplemental bills, one for the current fiscal year and one for the next, because the next year's roll was already set using the old value.
Two practical warnings: supplemental bills are mailed to you directly, and mortgage escrow accounts typically do not pay them. Budget for it, or the first year of homeownership will cost more than your closing estimate suggested.
Prop 19: Taking Your Tax Base With You After 55
For decades, Prop 13 had a lock-in problem: empty nesters wouldn't downsize because selling meant losing their low assessed value. Proposition 19, effective April 2021, addressed this. Homeowners who are 55 or older (or severely disabled, or victims of a wildfire or declared disaster) can sell their home and transfer their old factored base year value to a replacement home:
- Anywhere in California (the old rules limited transfers to a handful of counties)
- Up to three times in a lifetime
- To a home of any price, with an adjustment if you buy up
- The replacement must be bought or built within two years of selling the original home
The buy-up math, using the state Board of Equalization's own example: your current home has a taxable value of $300,000 and sells for $600,000. You buy a replacement for $700,000. The $100,000 excess is added to your transferred base: your new taxable value is $400,000, not $700,000. At a 1.1% rate, that's roughly $4,400 a year instead of $7,700, a saving of $3,300 every year going forward. If you buy a replacement at or below your sale price, your taxable value simply carries over unchanged ($300,000 in this example).
The claim isn't automatic: you file a form (BOE-19-B for the age-based transfer) with the county assessor, generally within three years of buying the replacement.
Prop 19's Other Half: Inherited Homes
Prop 19 also took something away. Before 2021, parents could pass a home (plus up to $1 million of other property each) to children with no reassessment, even if the kids rented it out. Now the parent-child exclusion applies only to a family home or farm that the child moves into as their primary residence within one year of the transfer. Inherited rentals, vacation homes, and houses the children don't occupy are reassessed to full market value.
Even for a child who does move in, the exclusion is capped: the old taxable value plus an inflation-adjusted allowance, currently $1,044,586 (for transfers from February 2025 through February 2027; the figure adjusts every two years). Worked example from the BOE: a home with a taxable value of $300,000 and a market value of $1.5 million at transfer. The excluded amount is $300,000 + $1,044,586 ≈ $1.34 million; the excess above that gets added, so the child's new taxable value is about $455,000, still a fraction of the $1.5 million a buyer would be assessed, but no longer the parents' untouched $300,000.
Two Programs Californians Forget to Claim
- Homeowners' exemption: $7,000 off assessed value for your owner-occupied primary residence, worth about $70 a year. Small, but it's a one-time form (BOE-266) and it stays in effect as long as you live there. A surprising number of eligible owners never file it.
- Property Tax Postponement (PTP): homeowners who are 62+, blind, or disabled, with household income of roughly $55,000 or less and at least 40% equity, can defer their property taxes entirely. The state pays the county; you repay with 5% simple interest when the home sells or transfers. Funding is limited and applications (October–February each cycle) are first-come, first-served through the State Controller's Office.
What This Means Depending on Who You Are
| Situation | What matters most |
|---|---|
| First-time buyer | Budget on ~1.1–1.3% of your purchase price, not the seller's old bill, and expect a supplemental bill escrow won't cover |
| Long-time owner | Your low base is an asset. Renovating adds only the new construction at market value; selling resets everything |
| Age 55+, thinking of moving | Prop 19 lets you carry your tax base anywhere in the state, up to three times. Run the buy-up math before assuming a move is unaffordable |
| Inheriting a home | Move in within a year and file the claim, or expect reassessment to market value. Renting it out ends the exclusion |
| Senior on limited income | Check the PTP deferral program and don't skip the homeowners' exemption |
Bottom Line
California's system rewards holding and penalizes moving, which is exactly why Prop 19's transfer rules matter so much for anyone over 55, and why its inheritance rules catch so many families off guard. If you're comparing what you'd actually pay in different California counties, our California pages break down rates by county, and our guides to assessed vs. market value and estimating taxes before you buy cover the fundamentals that apply everywhere.