Supplemental Property Tax Bill After You Buy a California Home: What It Is and When It Is Due

Solve Lending & Realty is a mortgage and real estate brokerage, not a tax advisor. Confirm your own bill with your county tax collector or a tax professional.

What a supplemental tax bill is and why new buyers get one

Most buyers expect one property tax bill a year, paid out of the impound account their lender set up at closing. Then a second envelope arrives. It is due on the date mailed, and if it was mailed in July through October 2026, its first installment is delinquent after 5 p.m. on December 10, 2026, when a 10 percent penalty is added if it is unpaid.

California reassesses a property when it changes hands or when new construction is completed. The State Board of Equalization’s Supplemental Assessments page (read October 15, 2026) calls these “supplemental events.” The assessor subtracts the old assessed value from the new one, and the difference becomes a supplemental assessment. That assessment is billed separately from the regular annual bill, for the part of the fiscal year you owned the home. A fiscal year runs July 1 through June 30.

Two things follow from that. The bill can arrive months after closing: Los Angeles County’s tax collector, in its secured property tax FAQ updated October 2024, says processing “generally” takes “approximately six months.” And if the new value is lower than the old one, the supplemental is negative and produces a refund instead of a bill.

Why your impound account usually does not pay it

This is the part that surprises people. The BOE is direct about it: “lending agencies do not receive the original or a copy of the supplemental tax bill even if they are otherwise being sent and are paying the owner’s annual tax bills.”

The county tax collectors’ own pages, read October 15, 2026, say the same thing their own way. Orange County: supplemental taxes “are generally not covered by impound accounts and a copy of the bill is NOT sent to your mortgage lender.” San Diego County: supplemental bills “are not sent to a lender for payment.” Riverside County: “you must contact your lender to determine who will pay the bill.” Los Angeles County: “Lenders/financial institutions do not usually pay Supplemental Secured Property Tax Bills.”

So the safe assumption is that the supplemental bill is yours to pay unless your servicer confirms in writing that it will pay it.

When it is due, and the December 10 and April 10 delinquent dates

The schedule depends on the month the bill is mailed. Revenue and Taxation Code section 75.52 says “Taxes on the supplemental bill are due on the date mailed” and sets when each installment becomes delinquent. The Orange County and Riverside County tax collectors print the July-through-October dates on their own pages (read October 15, 2026):

• Mailed July through October 2026: the first installment is delinquent after 5 p.m. on December 10, 2026. The second is delinquent after 5 p.m. on April 10, 2027; that date is a Saturday, so the next-business-day rule below applies.
• Mailed November through June: the first installment becomes delinquent at 5 p.m. on the last day of the month after the month it was mailed. The second becomes delinquent at 5 p.m. on the last day of the fourth calendar month after that.

If a delinquent date falls on a Saturday, Sunday or legal holiday, section 75.52 moves the time of delinquency to “5 p.m. or at the close of business, whichever is later, on the next following business day.” Section 2619 says the same for December 10 and April 10. December 10, 2026 is a Thursday, so that date holds this year. April 10, 2027 is a Saturday, so for a bill mailed July through October 2026 the second installment’s delinquency moves to the next business day, Monday, April 12, 2027, unless your county closes that day.

Section 75.52 sets the penalty: “If the taxes due are not paid on or before the date and time they become delinquent, a penalty of 10 percent shall attach to them.” A cost is added after the second installment goes delinquent. That cost varies by county: Orange County lists “$23.00,” San Diego County “$10.”

Your bill prints its own delinquent dates. Those are the dates to use. If you pay by mail, Orange County advises mailing “at least 3 days prior to delinquent date.”

Why some buyers get two supplemental bills

The timing of your closing decides it. Per the BOE:

• Closed June 1 through December 31: “only one supplemental tax bill or refund check is issued.”
• Closed January 1 through May 31: “two supplemental tax bills or refunds are issued. The second bill or refund accounts for the property’s change in value for the entire 12 months of the coming fiscal year, beginning on the following July 1.”

The second bill exists because the next year’s regular roll was already set before your purchase showed up on it. So a spring 2026 buyer may see two supplemental bills on top of the regular annual bill.

How the amount is calculated

The BOE’s page says the bill covers the period from the first day of the month after the purchase to the end of the fiscal year. Revenue and Taxation Code section 75.41 sets the same start: a change in ownership is “presumed to have occurred on the first day of the month following the date on which change in ownership or completion of new construction occurred.” The tax on the supplemental value is then “adjusted by a proration factor to reflect the portion of the tax year remaining” and “computed in two equal installments.”

Your county’s tax collector can tell you the actual rate for your parcel.

When a supplemental means a refund

If the purchase price, or the value the assessor enrolls, is lower than what was on the roll before, the supplemental is negative. The BOE says the auditor-controller “will issue one, or possibly two, supplemental refund(s).” San Diego County notes that the refund check “can be applied to any other open bills you may have on your parcel.” Orange County says refunds are “generally mailed within 90 days of the assessment being enrolled.” Other counties’ timing was not checked.

A refund on the supplemental does not change what you owe on the regular annual bill.

Filing the homeowners’ exemption on a supplemental bill

The homeowners’ exemption takes $7,000 off the taxable value of a qualifying owner-occupied home, per the BOE’s Homeowners’ Exemption page (read October 15, 2026). It is one filing, on form BOE-266 from your county assessor, and it is not applied automatically.

For a supplemental assessment, the current BOE-266 (REV. 14, 07-25) sets two clocks:

• File by 5 p.m. on the 30th day after the date of the Notice of Supplemental Assessment, and the full exemption (up to the amount of the supplemental assessment) may apply, if it has not already been applied to the property for that year.
• File after that, but on or before the date the supplemental bill’s first installment becomes delinquent (December 10, 2026, for a bill mailed July through October 2026), and 80 percent may be allowed. After that, none on the supplemental.

The BOE adds a condition: you must occupy the home as your principal residence within 90 days of the purchase date, and the exemption on a supplemental is prorated from the purchase date through June 30. If the home already had the full exemption for the year, there is no additional exemption on the supplemental.

For the regular annual roll, the same form governs: by 5 p.m. February 15 for the full exemption; February 16 through 5 p.m. December 10 for 80 percent.

Supplemental bill vs. escrow shortage: two different things

The supplemental bill is a one-time catch-up for the months between your purchase and the point where the regular roll reflects your value.

An escrow shortage is something else. Federal rules (Regulation X, 12 CFR 1024.17) require your servicer to analyze your escrow account at the end of each computation year. A “shortage” is “an amount by which a current escrow account balance falls short of the target balance at the time of escrow analysis.” Once your new value reaches the regular annual bill your servicer pays, that bill may be larger than the amount your escrow was set up to cover, and the next analysis may show a shortage and a new monthly escrow amount.

Paying the supplemental bill yourself does not, by itself, prevent a later escrow shortage. Ask your servicer how your escrow was set up and when the next analysis runs.

County by county

The schedule above is state law and applies in every county. What each county’s own pages add (read October 15, 2026):

• Orange: schedule stated for bills mailed “between July 1 and October 30”; impounds “generally not covered”; refunds generally within 90 days; second-installment cost $23.00.
• Riverside: schedule stated for bills mailed “between July 1 and October 31”; contact your lender about who pays.
• San Diego: not sent to a lender; 10% penalty and a $10 second-installment charge; refund checks can be applied to other open bills on the parcel.
• Los Angeles: lenders “do not usually pay”; two bills for January 1 through May 31 events; processing about six months.
• San Bernardino: a lower value means “taxes will be refunded.”
• Ventura: we could not reach the county’s current page when we checked on October 15, 2026. The state schedule applies; use the dates printed on your bill.

Orange and Riverside print different end dates for the July-through-October window. The statute names the months, July through October, which is why the date printed on your bill is the one to trust.

Sources

• California Legislature, Revenue and Taxation Code section 75.52 (accessed 2026-10-23)
• California Legislature, Revenue and Taxation Code section 75.41 (accessed 2026-10-23)
• California Legislature, Revenue and Taxation Code section 2619 (accessed 2026-10-23)
• California State Board of Equalization, Supplemental Assessments (accessed 2026-10-15)
• California State Board of Equalization, Homeowners’ Exemption (accessed 2026-10-15)
• California State Board of Equalization, BOE-266, Claim for Homeowners’ Property Tax Exemption (sample, REV. 14, 07-25) (accessed 2026-10-15)
• Orange County Treasurer-Tax Collector, Supplemental Property Taxes FAQ (accessed 2026-10-15)
• Orange County Treasurer-Tax Collector, Supplemental Tax Bill (accessed 2026-10-15)
• Riverside County Treasurer-Tax Collector, Supplemental Tax Bill Information (accessed 2026-10-28)
• San Diego County Treasurer-Tax Collector, Supplemental Property Taxes (accessed 2026-10-15)
• San Diego County Treasurer-Tax Collector, Supplemental Tax FAQ (accessed 2026-10-15)
• Los Angeles County Treasurer and Tax Collector, Secured Property Taxes FAQs (updated October 2024) (accessed 2026-10-15)
• Los Angeles County, Supplemental Secured Property Tax Bill, field descriptions (accessed 2026-10-15)
• San Bernardino County Assessor-Recorder-County Clerk, FAQ: notice of supplemental assessment (accessed 2026-10-15)
• eCFR, 12 CFR 1024.17, Escrow accounts (Regulation X) (accessed 2026-10-15)