What Is a San Bernardino Supplemental Tax Bill?

A San Bernardino supplemental tax bill is a one-time property tax charge the county sends after a sale or completed construction changes your home’s assessed value. It covers the difference between the old assessed value and the new one, prorated for the months left in the fiscal year (July 1 through June 30). It is separate from your annual secured tax bill, and it comes directly to you rather than to your mortgage company.¹ The underlying rule comes from Proposition 13, which caps the base rate at one percent of full cash value and limits reassessments to specific triggering events.²

What Triggered Your Bill

California Revenue and Taxation Code Section 75 requires the assessor to update the tax roll immediately when real property changes hands or new construction finishes, instead of waiting for the next annual cycle.³ A change in ownership covers any sale or legal transfer of title, and the property gets reappraised at its full cash value as of the transfer date.⁴

New construction counts once the work is complete, which the statute defines as the earliest of three dates: when the property is available for the owner’s use, when it is occupied with the owner’s permission, or when it can be functionally used.⁵ Adding a bedroom, building a pool, or putting up a detached garage qualifies. Routine maintenance and minor repairs do not.

How the Amount Is Calculated

The San Bernardino County Assessor sets a new appraised value as of the sale or completion date and subtracts the prior assessed value already on the roll. The difference is your supplemental assessment. Buy a home for $600,000 when the previous assessed value was $400,000, and the supplemental assessment is $200,000.

The county then applies the current tax rate (the base one percent plus any local voter-approved bonds) and prorates the result based on how many months remain in the fiscal year. The effective date is the first day of the month after the event. A sale closing in October has a November 1 effective date, leaving eight months and a proration factor of about 0.67. A December closing takes effect January 1, with six months left and a factor of 0.50.⁶ On the $200,000 example with a December close, you multiply $200,000 by the tax rate, then by 0.50, to get the bill.

If the new assessed value is lower than the prior value, the supplemental assessment is negative and the county issues a refund rather than a bill. The refund is paid separately; it does not reduce what you still owe on your existing annual tax bill, which you must pay in full regardless.⁶

Why You May Get Two Bills

If the triggering event falls between January 1 and May 31, you get two supplemental bills instead of one. The first covers the remaining months of the current fiscal year. The second covers the entire next fiscal year starting July 1, because that upcoming year’s annual roll was already set at the old assessed value based on the prior January 1 lien date.⁶

Events between June 1 and December 31 produce only one bill. A June event rolls forward to a July 1 effective date, so it generates a single bill covering the full twelve months of the new fiscal year.⁶

Delinquency Dates and the Ten Percent Penalty

Each supplemental bill has two installments, and the deadlines depend on when the county mails it. Bills mailed between July and October follow the familiar annual-roll calendar: first installment delinquent December 10, second delinquent April 10. Bills mailed between November and June use a rolling schedule tied to the mailing month. The first installment becomes delinquent on the last day of the month after mailing, and the second installment becomes delinquent four months after that. A bill mailed in February, for instance, has a first-installment delinquency date of March 31 and a second-installment date of July 31.

Miss a delinquency date and a ten percent penalty attaches automatically to the unpaid amount.⁷ After the second installment goes delinquent, the county piles collection costs on top. The actual delinquency dates are printed on the bill, and they often will not line up with the December 10 and April 10 dates you know from your annual bill, so read them before you file the bill away.

Why Your Mortgage Company Won’t Pay This

This is where most new homeowners get burned. San Bernardino County mails supplemental tax bills directly to the property owner, not to the lender.¹ The county’s own annual tax statement spells it out: “Supplemental tax bills are not sent to your mortgage company.”⁸

Your mortgage impound account covers annual secured property taxes and insurance. A supplemental bill is a one-time adjustment outside that arrangement. If you assume the lender will pick it up, it goes delinquent and the ten percent penalty hits. You can forward the bill to your lender’s tax department, and some will pay it from escrow surplus if the account has enough. The default, though, is that you pay it yourself.¹

How to Pay

San Bernardino County takes supplemental tax payments online, by phone, by mail, and in person. Online or phone payments drawn from a checking or savings account are free. Credit card payments carry a processing fee set by the card vendor.⁹ Online payments go through MyTaxCollector.com; phone payments can be made at (909) 387-8308 or (760) 241-8829.

Mailed payments go to SBC Tax Collector, 268 West Hospitality Lane, First Floor, San Bernardino, CA 92415-0360. Include the payment stub and write your parcel number on the check. In-person payments are accepted at the Tax Collector’s Office, Monday through Friday, 8 a.m. to 5 p.m.⁹ If you misplace the bill, look it up on MyTaxCollector.com using your parcel number. Each supplemental bill has its own assessment number (ASMT), which is different from the reference number on your annual bill.

Exemptions That Can Lower the Bill

The homeowners’ exemption removes $7,000 from your assessed value and can apply to a supplemental assessment. If the prior owner did not have the exemption on the property, you can claim it on your supplemental bill as long as you move in within 90 days of the ownership change or construction completion.¹⁰ The dollar savings on a single supplemental bill are modest, but skipping the filing also costs you the ongoing annual exemption.

Proposition 19 can do much more. If you are 55 or older, severely disabled, or a victim of a wildfire or natural disaster, you can transfer your old property’s base year value to a replacement home anywhere in California. You must buy or build the replacement within two years of selling the original and file for the homeowners’ exemption on the new property within one year of the transfer. When the replacement costs the same as or less than the original, the full base year value carries over. When it costs more, the difference gets added to the transferred value.¹¹ A successful transfer sharply reduces the supplemental assessment on the new home.

Checking the Bill and Filing an Appeal

Before you pay, compare the bill against the Notice of Assessed Value Change the assessor mailed earlier. That notice shows the parcel number (APN), the event date, and the new base year value. Verify the event date first, because it drives the proration factor and the whole dollar amount. Then compare the new base year value to what you actually paid or spent on construction. If the assessor’s number is higher than your purchase price in an arm’s-length sale, the bill is likely overstated.

You have 60 days from the mailing date of the supplemental bill to file an appeal with the San Bernardino County Assessment Appeals Board.¹² That window is strict and shorter than the regular-roll appeal period. The strongest cases rest on a documented gap between the assessor’s value and your purchase price: gather the closing documents, the settlement statement, and your lender’s appraisal. For construction, bring the invoices and permits. Pay the bill by the delinquency date while the appeal is pending; if you win, the county refunds the overpayment.

1
San Bernardino County Assessor-Recorder-County Clerk. What Is a Supplemental Tax Bill
2
Justia. California Constitution Article XIII A – Tax Limitation
3
California Department of Tax and Fee Administration. Property Tax Annotations – Supplemental Assessment
4
California Legislative Information. California Revenue and Taxation Code 75.10
5
California Legislative Information. California Revenue and Taxation Code 75.12
6
California State Board of Equalization. Supplemental Assessment
7
California Legislative Information. California Revenue and Taxation Code RTC 75.52
8
San Bernardino County Auditor-Controller/Treasurer/Tax Collector. Annual Tax Bill Important Information
9
San Bernardino County. Property Tax Deadline: Convenient Ways to Pay
10
Legal Information Institute. California Code of Regulations Title 18 Section 135.5
11
California State Board of Equalization. Proposition 19 Fact Sheet
12
Justia. California Revenue and Taxation Code Article 6 – Collection of Supplemental Taxes