Property Taxes- Supplemental


Supplemental Tax Bills are generated due to a reassessment of the value of property due to an event such as:

  • A change in ownership (property sold or transferred, someone being added or removed from the Deed, placing into or removing the property from a Trust, etc.)
  • Completed construction (improvements, new buildings, some landscaping)

When the Assessor’s office is made aware of these events, they reassess the property’s value to either bring the whole property in line with market value (in ownership changes) or to add the value of the new construction to the property. These changes in value are billed separately from the annual tax bill so as to avoid the confusion from bills being canceled and reissued.

There are three reasons why an owner might receive more than one supplemental tax bill.

1. The supplemental event occurred between January 1 and May 31

An event occurring between January 1 and May 31 will generate a second supplemental assessment for the subsequent fiscal year affected. The second bill is generated because the annual roll assessment created for the coming fiscal year does not reflect the change in value generated by that event, and must also be adjusted to reflect the difference.

2. A prior owner had a supplemental event in the same fiscal year

When a series of supplemental events take place within the same fiscal year for different owners, there may also be multiple supplemental tax bills. If the bill for the prior owner’s supplemental event is for the same fiscal year in which you took ownership, you will receive a prorated portion of that bill for the time period you owned the property.

3. Multiple Supplemental Events Occurred While You Owned the Property

If multiple supplemental events (changes in ownership and/or new construction) occur while you own the property, you will receive one or more supplemental bills for each of these events. Supplemental assessments are generated for each event.

No, Supplemental Tax Bills are mailed directly to you. It is your responsibility to contact your lender to determine who will pay the Supplemental Tax Bill.

There are two types of Supplemental Tax Bills, secured and unsecured.

Secured Supplemental Tax Bills are issued to the current real property owner and are attached by a lien to the property. If you are not the current real property owner, and you have received a Secured Supplemental Tax Bill please contact the Tax Collector’s Office at (805) 781-5831 or by email at [email protected]

Unsecured Supplemental Tax Bills are issued to prior owners, or on unsecured property such as mobilehomes and possessory interest assessments. There is no real property to attach the lien to, and the bill is issued to the individual. If you currently own the real property referenced on the bill and you have received an Unsecured Supplemental Tax Bill please contact the Tax Collector’s Office at (805) 781-5831 or by email at [email protected]

If your Supplemental Tax Bill is not paid by the end of the fiscal year the property becomes tax-defaulted. If the taxes remain unpaid for a maximum of five years following tax-default, your property becomes subject to the County Tax Collector's Power to Sell.  See Payment of Delinquent Property Taxes.

If your Supplemental Tax Bill was Unsecured at billing, different laws apply. If your bill is not paid by June 30, and is given a prior year tax status a lien may be recorded which will affect your credit. Additional fees, interest and a Release of Lien Fee will be charged, in addition to the original tax amount. Delinquent collection cost(s) may also be added as collection efforts are taken.

Normally Supplemental Tax Bills can take 6-12 months from the date of the ownership or construction completed, however in the event of multiple taxable events have taken place, (Example: Construction followed by change in ownership) this may delay bills longer than 12 months.

The date on which Supplemental Tax Bill(s) become delinquent varies, depending upon when they are mailed by the County Tax Collector.

For Bills Mailed in: 1st Installment Delinquent Date 2nd Installment Delinquent Date
July December 10 April 10
August December 10 April 10
September December 10 April 10
October December 10 April 10
November December 31 April 30
December January 31 May 31
January February 28 June 30
February March 31 July 31
March April 30 August 31
April May 31 September 30
May June 30 October 31
June July 31 November 30

Penalties of 10% are added to any installment which is not paid before the delinquency date, and an additional delinquent cost is added to a late 2nd installment.

Yes, the Supplemental tax Bill is in addition to the annual tax bill. Both bills must be paid by their respective delinquent dates. For information on the annual tax bill, see the section, Secured Property Taxes.

You may be eligible for an Exemption on your Supplemental Tax Bill, which would result in a reduction of taxes. Applications for homeowner, veteran, church, welfare, or other exemptions may be obtained at Property Exemption Information or from the Assessor's Office at (805) 781-5643.

  • The fiscal year for which the taxes are assessed.
  • The legal description of the property.
  • The old and the new Assessed Values and the difference (net Supplemental Value) upon which the tax is computed.
  • The type and amount of any Exemptions, if applicable.
  • The total amount of taxes due.
  • The due and delinquent dates.

New construction includes any addition to real property or any substantial alteration to an existing structure which requires a building permit.

A change in ownership occurs when title to the property is transferred. Transfer can be caused by sale, inheritance, or seizure.

Exclusions may be granted, but require the filing of documentation with the Assessor’s Office. For claim forms or further information regarding the requirements for filing exclusions contact the Assessor at (805) 781-5643.

The Assessor determines a new value for the property. The Assessor then calculates the difference between the new value (set at the time of purchase or completion of new construction) and the previous value. This results in the Supplemental Assessment Value. Once the new assessed value of your property has been determined, the Assessor will send you a Notice of Supplemental Assessment.


New value at date of purchase or completion of new construction $220,000
Assessed Value for current fiscal year -200,000
Supplemental Assessment Value $ 20,000

Supplemental Taxes are calculated based on the difference (or increase) in values. As a result, one or more Supplemental Tax Bills will be issued. 
If the reassessment results in a reduction in value, a refund will be issued by the Auditor-Controller's Office. A reduction in value will not reduce the amount due on the annual tax bill. The annual tax bill must be paid in the amount originally billed before a refund can be issued.

Yes, however, you should first discuss the matter with the Assessor's Office to schedule an informal assessment review. If the matter is not resolved to your satisfaction, there is an Assessment Appeals Board established to formally appeal the assessment. Appeals must be filed within sixty (60) days of the mailing date shown on the Notice of Supplemental Assessment sent by the County Assessor’s Office.

If you are appealing your assessment, your Supplemental Tax Bill(s) should be paid before they become delinquent. If left unpaid, penalties may accrue during the appeal process. If the outcome of your appeal results in a refund, it will be issued by the Auditor-Controller's Office.

Further information regarding the appeals process can be obtained by calling (805) 781-5080, or writing to: County Clerk, Room D-120, County Government Center, San Luis Obispo, California, 93408. Assessment Appeals

No, the California Revenue and Taxation Code does not authorize the County Tax Collector to remove penalties in this situation.

If the reassessment results in an increase you will receive a Supplemental Tax Bill for the period that you owned the property. The new owner of the property will receive a separate Supplemental Tax Bill from their date of purchase. You may not receive the Supplemental Tax Bill until after you transfer the property to the new owner.

Check the dates used in prorating your Supplemental Tax Bill to ensure that the period covered is correct. If you believe the proration period is incorrect, contact the Assessor's Office at (805) 781-5643.

No, you are only taxed on the Supplemental Value for the remaining portion of the year, from the date you purchased the property or completed new construction. However, if the purchase date or the construction completion date was after January 1, you will receive an additional Supplemental Tax Bill for the following fiscal year.


How to Read Your Supplemental Tax Bill