Plain-language education
California supplemental property taxes, explained for buyers.
After you buy a home in California, the county reassesses it to its new market value, usually your purchase price, and you may receive an additional supplemental property tax bill. This page explains what triggers it, when it arrives, who pays it, and how to plan for it. It is educational information, not tax advice.
Why it happens
A change of ownership triggers a reassessment.
California’s Proposition 13 limits how much a property’s assessed value can rise each year, which is good for long-time owners. But when a property changes ownership, the law requires the county assessor to reassess it to its current market value, which for a new purchase is typically what you paid.
The reassessment is effective as of the first day of the month following the close of escrow. If the home’s new assessed value is higher than the old base value the seller had, the difference produces a supplemental tax.
How it is figured
The tax on the difference, prorated by year.
The supplemental bill is the property tax on the difference between your new assessed value and the seller’s old assessed value, prorated from the effective date to June 30, the end of the fiscal year. In dollar terms it depends on your purchase price, the seller’s old base, your local tax rate, and how many months are left in the fiscal year when you close.
How many bills you receive depends on when you close. If the change of ownership happens between June 1 and December 31, you generally get one supplemental bill covering the rest of that fiscal year. If it happens between January 1 and May 31, you generally get two bills: one for the rest of the current fiscal year and a second for the full following fiscal year.
When it arrives
Months later, and paid on top of your regular bill.
After escrow closes, the county assessor appraises the property and mails a Notice of Supplemental Assessment. The supplemental bill is normally issued within about six months of the close of escrow, though timing varies by county workload and can sometimes take longer. Even when the bill arrives months later, its effective date reaches back to the first of the month after your purchase.
Payment is commonly due in two installments, with dates that depend on when the bill is mailed. The supplemental bill is separate from, and in addition to, your regular annual secured property tax bill.
Who pays
The buyer plans for it. Plan to set funds aside.
As the new owner, you are responsible for the supplemental tax, and lender impound or escrow accounts typically do not cover these bills. The practical advice buyers hear most is to plan for it: ask roughly what the supplemental amount may be, set money aside at closing, and be ready for a bill to arrive in the months after you move in.
Because the assessment is based on your purchase, you can often estimate the direction of the bill yourself: if homes in the area have appreciated since the seller’s base year, a supplemental bill is likely. After the reassessment, your regular annual tax bill is generally based on your new purchase price going forward.
Your next step
Add it to your budget before you buy.
Supplemental taxes are one of the hidden costs buyers forget until the bill arrives. I help North Laguna Creek buyers build a complete budget, including closing costs and the taxes that follow, so there are no surprises after the move. Let’s talk about how I can help you.
Important: This page is educational and informational only. It is not tax, legal, or financial advice, and it is not a substitute for consulting a qualified tax professional or your county assessor about your specific situation. Assessed values, rates, and timing vary by county and change over time. CA DRE #01194604.