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Learn about supplemental assessments
Property reassessments upon changes in ownership or completion of new construction.
Supplemental assessments
Changes in ownership or completed new construction are referred to as 'supplemental events.' They result in supplemental tax bills that are in addition to the annual property tax bill.
How it works
- Supplemental event: This triggers a reassessment of a property's value. It can be a change in ownership (like buying a house) or new construction (adding a room).
- Market value determination: our office determines the property's current fair market value based on the date of the event.
- Net supplemental value calculation: our office then subtracts the property's prior assessed value from its newly assessed value. The difference between the two is the supplemental value that will be assessed and enrolled as a supplemental assessment.
- Enrollment of new value: The net supplemental value is added to the tax roll, leading to a higher or lower tax bill (depending on the change in value).
Example of supplemental notice assessment from our office:
- New value at date of purchase or completion of new construction: $250,000
- Less prior assessed value: (200,000)
- Equals net supplemental assessment: $50,000
Number of notices
One, or possibly two, supplemental tax bill(s) will be generated and mailed by the Office of the Treasurer and Tax Collector.
- When the supplemental event occurs from January 1 through May 31, two (2) supplemental tax bills are issued. The second bill accounts for the property's change in value for the entire 12 months of the coming fiscal year, beginning on the following July 1.
- When the event occurs June 1 through December 31, one (1) supplemental tax bill is issued. This bill accounts for the property's change in value for the period between the first day of the month following the event date and the end of the fiscal year (the following June 30).
Example
- A supplemental event occurs in March 2024
- Generates 2 supplemental bills. One bill covers the rest of the fiscal year 2023-2024 from April to June. The second notice covers the full fiscal year 2024-2025 from July to June.
- A supplemental event in September 2024
- Generates 1 supplemental bill for the rest of the fiscal year 2024-2025 from October to June.
Calculating supplemental taxes
An increase (or decrease) in assessed value results from the reappraisal. This value is prorated based on the number of months remaining in the fiscal year. A fiscal year runs from July 1 through June 30. Monthly proration factors (see below) are used to calculate the taxes owed.
Taxes are the product of the supplemental assessment, tax rate, and the monthly proration factor. The Office of the Treasurer & Tax Collector will mail the supplemental tax (bill)s within 60 days of the notice of Supplemental Assessment. If your new assessed value is lower than the previous assessed value, you will get a refund.
Use our supplemental tax calculator or read the below for an example.
Example
- A homeowner completed a new Accessory Dwelling Unit on March 2024. We determined the increased value to be $150,000.
- Supplemental tax bill #1
- Multiply the supplemental assessment, tax rate, and proration factor
- $150,000 (supplemental) X 1.17973782% (tax rate) X .25 (proration rate)
- The proration rate of .25 covers April 1 which is the first day of the month after the supplemental event to the end of June.
- Equals $442.40 for the first supplemental tax bill. This tax covers the remainder of fiscal year 2023-2024 for 3 months April, May, and June.
- Supplemental tax bill #2
- Multiply the supplemental assessment, tax rate, and proration factor
- $150,000 (supplemental) X 1.17973782% (tax rate) X 1.00 (proration rate)
- A second supplemental for approximately $1,769.60. This cover the full fiscal year 2024-2025 for 12 months from July to June.
Proration factors
Use these monthly proration factors to calculate the supplemental taxes.
Tax effective: January 1, Months remaining in the fiscal year = 6 months, Proration factor = .50
February 1 = proration factor .42
March 1 = proration factor .33
April 1 = proration factor .25
May 1 = proration factor .17
June 1 = proration factor .08
July 1 = proration factor 1.00
August 1 = proration factor .92
September 1 = proration factor .83
October 1 = proration factor .75
November 1 = proration factor .67
December 1 = proration factor .58
Your rights
Your right to an informal review
Contact our office for an informal review if you believe the assessment is incorrect. Contact us at 628-652-8100 or assessor@sfgov.org
Your right to appeal your escape property assessment
You also have the right to a formal appeal of the assessment. The Assessment Appeals Board process involves the following steps.
- The filing of an Application for Changed Assessment,
- A hearing before an appeals board, and
- A decision by the appeals board.
Contact the Clerk's Office at (415) 554-6778 or visit their website (linked below) for more information on filing an application.
You may file the formal appeal after you receive the tax bill from the Office of the Treasurer & Tax Collector. File the application no later than 60 (sixty) calendar days from the date of mailing printed on the escape tax bill or the postmark date, whichever is later.