California property taxes start from Proposition 13 (Prop 13), the 1978 law that sets a 1% base rate on a home's assessed value. Local voter-approved add-ons, such as school bonds and parcel taxes, push the effective rate to roughly 1.1% to 1.25% in most Bay Area communities. When you buy, the assessed value resets to your purchase price and can then rise no more than 2% a year. In your first year, a one-time supplemental tax bill covers the jump from the prior owner's assessed value to your purchase price. Some newer communities also add Mello-Roos, a special tax that funds local infrastructure, on top of all of this.
This page covers the Prop 13 base rate and the 2% cap, assessed value versus market value, what triggers a reassessment, the supplemental bill, and how Prop 19 and Mello-Roos fit in.
The Prop 13 base
California's base property tax rate is 1% of assessed value, set by Prop 13 when voters passed it in 1978. Local voter-approved items stack on top, so most Bay Area homeowners pay an effective rate around 1.1% to 1.25%, sometimes higher. Your exact figure depends on your parcel; the county assessor can confirm.
In practice your combined effective rate runs higher than the bare 1%. Local voter-approved items (school bonds, water districts, and similar special assessments) stack on top of the 1% base, so most Bay Area homeowners land somewhere around 1.1% to 1.25% of assessed value, and sometimes higher. The exact figure depends on your specific parcel and the districts it sits in, which your county assessor can confirm.
The 2% annual cap
While ownership does not change and you add no new construction, Prop 13 lets the assessor raise your assessed value by at most 2% per year. That cap has held since 1978. It is the quiet half of Prop 13, and over time it matters more than the headline rate.
This is the quiet half of Prop 13, and it matters more over time than the headline rate. A home that does not change hands ratchets up only 2% a year on the tax rolls, even when the market jumps far faster.
Assessed value vs market value
You are taxed on assessed value, not on market value. Assessed value is usually anchored to your purchase price at the time you bought and creeps up only about 2% a year. That is why a long-time owner next door can pay far less on a nearly identical house.
That gap explains why a long-time owner next door pays far less than you do on a nearly identical house. Their assessed value started at an old purchase price and crept up only about 2% a year ever since. Your assessed value resets to what you just paid. Two similar homes, two very different tax bills, and both are working exactly as Prop 13 intends.
What triggers a reset (reassessment)
A sale or change of ownership triggers reassessment: the assessor re-anchors your assessed value to the new purchase price, generally what you actually paid. Not every change is a full reset, though. Certain improvements add only the value of that improvement rather than re-rating the whole property.
Not every change is a full reset. Certain improvements add only the value of that improvement to your assessment rather than re-rating the whole property, which is why a remodel and a sale are treated very differently.
The supplemental tax bill, the year-one surprise
The supplemental bill is a separate, one-time catch-up bill covering the gap between the seller's old, lower assessed value and your new, higher basis. It arrives months after closing, commonly 6 to 18 months later (timing varies by county), and an impound/escrow account often does not cover it, so set cash aside.
It arrives months after closing, commonly 6 to 18 months later, with exact timing varying by county. It bills you for the difference between the seller's old assessed value and your new, higher basis, prorated for the part of the fiscal year you owned the home. California's fiscal year, the 12-month period the county uses for property taxes, runs July 1 to June 30, with the regular bill split into two installments. (Many counties set the delinquency dates at December 10 for the first installment and April 10 for the second; confirm your own dates with the county assessor, since this is the kind of detail that varies.)
People miss the supplemental bill because nothing in the buying process puts it in front of them. Zillow estimates, lender worksheets, and the regular two-installment schedule all tend to show only the ordinary bill. Most important: an impound or escrow account (the account your lender uses to pay your property taxes and homeowner's insurance out of your monthly mortgage payment) often does NOT cover the supplemental bill. It usually comes straight to you, the homeowner, as a bill you pay out of pocket. So set cash aside for it.
How large is it? That depends entirely on the gap between the old assessed value and your purchase price. As a purely illustrative example, not a quote for any specific home: if you buy well above a long-time seller's old assessed value, the one-time supplemental bill can run several thousand dollars. Your own number depends on your purchase price, your county, and when in the fiscal year you closed. It is worth budgeting for alongside your other closing costs.
A brief note on Prop 19
If you inherit a home, Prop 19 (the 2021 measure) can trigger reassessment unless conditions are met: an heir generally must move in within about a year as a primary residence to keep the parent's tax base, and even then a value cap applies. Rules are fact-specific; confirm with a tax professional or estate attorney. For the bigger picture, see estate planning for Bay Area homeowners.
How Mello-Roos is separate
Proposition 13 and Mello-Roos are two different things that often get confused. Prop 13 is a statewide law: it sets the base 1% property-tax rate on assessed value and caps how fast that assessed value can grow, no more than 2% a year, and it applies to nearly every property in California. Mello-Roos is a separate, local, voter-approved special tax that applies only inside a designated Community Facilities District (CFD), mostly in newer developments, and it funds that district's own schools, roads, and parks. The key difference: Mello-Roos does not follow Prop 13's 2% cap, so its charge is set by the bond terms rather than by the assessed-value formula.
Mello-Roos is a separate recurring special assessment that some newer communities add on top of the 1% base to fund local infrastructure. It is not Prop 13, and it is not the supplemental bill. In the East Bay these districts cluster in newer master-planned tracts, such as parts of Dublin and San Ramon. If your home sits in one of these districts, you can read more on the dedicated Mello-Roos page.
Working with me
If you want help projecting your year-one tax bill, including the supplemental bill that catches so many buyers, reach out to me. I have walked buyers through this exact surprise, and I am glad to talk it through in English and Russian so you can budget with your eyes open before you close. You can email me at lilyagaripova@gmail.com or call or text (415) 910-3958.
Lily Garipova
lilygaripova.com | Fremont, California
FAQ
Why is my neighbour's property tax bill lower than mine?
Because property tax is anchored to assessed value, and assessed value usually resets to the purchase price each time a home sells. A long-time owner's assessed value started at an old, lower price and rose only about 2% a year under Prop 13. Your assessed value reset to today's purchase price when you bought, so your bill is higher on a similar home.
What is the supplemental tax bill?
It is a separate, one-time catch-up bill issued after you buy. When your assessment re-bases to your purchase price, the supplemental bill covers the gap between the seller's old assessed value and your new, higher basis for the part of the fiscal year you owned the home. It is in addition to your regular property tax bill.
When does the supplemental bill arrive?
Usually months after closing, commonly 6 to 18 months later. The exact timing varies by county, so it can land well into your second year of ownership. Treat it as money you will owe later rather than a bill that has gone away.
Does my mortgage escrow pay the supplemental bill?
Often it does not. An impound or escrow account is set up to cover your regular property taxes and insurance, and the one-time supplemental bill frequently comes directly to you instead. Plan to pay it out of pocket, and check with your lender and county so you are not caught off guard.
What is the difference between Prop 13 and Mello-Roos?
Prop 13 is the statewide rule that sets the 1% base rate and caps annual increases at 2%. Mello-Roos is a separate, recurring special assessment that only some newer communities add on top of that base to fund local infrastructure. One applies almost everywhere; the other depends on whether your specific home sits in such a district.
Does remodeling raise my property taxes?
It can, but usually not by resetting your whole assessment. New construction generally adds only the assessed value of the improvement itself to your existing assessment, rather than re-basing the entire property to today's market value. Routine repairs and maintenance typically do not change your assessment at all; your county assessor draws the line.
How are property taxes calculated in California?
California property taxes are based on Proposition 13, which sets a 1% base rate on a home's assessed value. Local voter-approved add-ons, such as school bonds and parcel taxes, typically bring the effective rate to about 1.1% to 1.25%. When you buy, the assessed value resets to your purchase price and can rise no more than 2% a year after that. A one-time supplemental tax bill in your first year covers the gap between the prior owner's assessed value and your purchase price, and some newer communities add a Mello-Roos special tax on top.
Is Mello-Roos the same as Prop 13?
No. Proposition 13 is a statewide law that sets the base 1% property-tax rate and caps assessed-value growth at 2% a year for nearly every California property. Mello-Roos is a separate, local special tax that applies only inside a designated Community Facilities District (CFD), mostly in newer developments, and pays for that district's own infrastructure. Mello-Roos does not follow Prop 13's 2% cap, so it is an added charge rather than a change to how your base tax is calculated.
What is the true monthly cost of a $1.3M home in California once you add property tax and insurance?
The advertised payment usually shows only principal and interest, so it can understate the real number. Your full monthly cost is closer to PITI (principal, interest, taxes, and insurance), and in California the tax piece is set by your purchase price rather than the seller's old assessed value, so it resets higher when you buy. To make that concrete (illustrative only, mid-2026, not a live quote): at a rough 1.2% effective rate, the property tax on a $1.3M purchase price runs about $15,600 a year, or roughly $1,300 a month, and Bay Area homeowner's insurance on a home like this commonly lands somewhere around $2,000 to $5,000 a year, or about $170 to $420 a month. Homeowner's insurance has also climbed across much of the Bay Area, and some homes carry HOA dues or a Mello-Roos special tax (a separate charge some newer communities add to fund local infrastructure) on top. Treat any online estimate as a starting point, set cash aside for the supplemental bill in year one (a purchase that closes between January and May can produce two, one for the current tax year and one for the next), and ask for a line-by-line projection on the specific property before you offer.
California property tax looks lower than Texas at 1%. What is the catch?
The 1% base rate is real, but a few things sit underneath it. Voter-approved add-ons such as school bonds and parcel taxes usually push the effective rate to roughly 1.1% to 1.25%, and that percentage applies to California's higher home prices, so the dollar amount can still be large. When you buy, your assessed value resets to your purchase price instead of carrying over the seller's lower figure, a one-time supplemental bill catches up that difference in year one, and some newer communities add a Mello-Roos special tax (a local infrastructure charge) that the 1% rule does not cap. None of this is a hidden trap; it is simply how the pieces stack, and your exact total depends on your parcel and county.
Why would a neighbour with the same house pay far less property tax than a new buyer?
Because property tax is anchored to assessed value, and assessed value usually resets to the purchase price each time a home sells. A long-time owner's assessed value started at an old, lower price and rose only about 2% a year under Prop 13, while a new buyer's resets to today's purchase price, so two nearly identical homes can carry very different bills. This is the system working as intended, not a penalty aimed at new buyers. Once you own, your basis is locked the same way and can rise no more than 2% a year, so over time you become the long-time owner paying the lower bill on the street.
Can I take my Prop 13 tax base with me when I move under Prop 19 (age 55 and over)?
Yes, this is one of the situations Prop 19 was built for. If you are 55 or older (the rule also covers people with a severe disability and certain disaster victims), you can transfer your current assessed value, your Prop 13 tax base, to a replacement primary home anywhere in California, and you can do this up to three times. If the new home costs the same or less than your sale price your old, lower base moves with you, and if it costs more only the difference in value is added, so downsizing generally does not triple your tax. You claim it through the county assessor after you close, using their Prop 19 base-transfer form, and because the timing and eligibility rules are specific, confirm the details for your situation with the county assessor or a tax professional before you rely on this.
