By Paarth Shah, REALTOR® · August 10, 2026 · Silicon Valley / San Jose
If you bought a home in San Jose and a second property tax bill arrived a few months after closing, you were not billed twice. That is a supplemental property tax bill, and it is a normal part of buying in California.
Why it happens
Proposition 13 requires real property to be reassessed when it changes ownership or when new construction is completed. Since 1983, that reassessment takes effect on the first day of the month following the transfer or completion date, rather than waiting for the next January 1 lien date. The supplemental bill collects tax on the difference between the seller's old assessed value and your new one, for the remainder of that fiscal year.
How the math works
The county fiscal year runs July 1 to June 30. Santa Clara County takes the difference between the new value and the old January 1 value, multiplies it by a proration factor (the share of months left in the fiscal year), then applies the tax rate, generally 1 percent plus voter approved debt.
Hypothetical example, for illustration only. A San Jose buyer closes October 12. The prior assessed value was $600,000 and the new value is $1,400,000, a difference of $800,000. The reassessment is effective November 1, leaving 8 of 12 months in the fiscal year, a factor of 0.667. That gives $533,600. At a rate of roughly 1.25 percent, the supplemental bill would be about $6,670. Your own numbers will differ. The Assessor publishes a Supplemental Tax Estimator so you can run your actual figures.
One bill or two
Buyers who close between January 1 and June 30 usually receive two supplemental bills. The value for the coming fiscal year was already set on January 1 under the seller's old value, so both fiscal years need correcting.
Your lender probably will not pay it
This is where people get burned. Lenders do not receive a copy of the supplemental bill, and it is usually not prorated in escrow. If you have an impound account, call your servicer and confirm who is paying. The county is explicit that a misunderstanding with your lender is not grounds to waive penalties.
Timing
You should get a Notification of Supplemental Assessment roughly 60 days before the bill. Most bills are mailed within nine months of the event. The bill is payable in two installments. If mailed July through October, the delinquent dates are December 10 and April 10. If mailed November through June, the first installment is delinquent the last day of the following month and the second four months later. Late installments carry a 10 percent penalty plus a $20 cost.
Budget for it at closing rather than being surprised by it. If you want help estimating yours before you write an offer, reach out at paarth@brokerbela.com.
A supplemental property tax bill is issued when Santa Clara County reassesses your home after a change of ownership or new construction, and it charges tax on the increase in assessed value prorated over the months remaining in the fiscal year. It is separate from and in addition to your annual secured tax bill, and lenders do not receive a copy of it.
Sources
This is general market commentary, not financial, investment, or legal advice; figures are as of publication and can change. Verify specifics, including any school assignments, ratings, or boundaries, independently. Bela Realty & Investments is committed to Equal Housing Opportunity and does not steer clients toward or away from any neighborhood on the basis of a protected characteristic.