Computation of Supplemental Taxes

Supplemental refunds or bills are calculated based on the number of months remaining in the current fiscal year after the month in which a property transfer or after the date of new construction was completed. That is, if a supplemental event raises the annual tax by say $200 and there were six months left in the current fiscal year when the event occurred, the supplemental tax bill would be 50% of the $200, or $100.

If your property was purchased or new construction was completed between June 1 and December 31, only one supplemental tax bill or refund check is issued. However, if a supplemental event occurs between January 1 and May 31, a second supplemental bill or refund is issued. That second bill or refund will cover the entire 12-months of the coming fiscal year beginning on July 1.

That’s because the assessment roll created on the preceding January 1 Lien Date does not reflect the change in value that occurred after the Lien Date; hence, a second bill or refund must be created to account for the increase or decrease for the entire coming fiscal year.

If your property had multiple ownership changes and/or multiple new construction completions, you should have received separate supplemental tax bills to pay a pro-rata share of the increased taxes for each ownership change or new construction events completed.

Because a change in the tax due to a supplemental event becomes effective on the first day of the month following the month in which the event took place, monthly proration factors are used to calculate the taxes owed.

Taxes supplemental to the current roll are computed by first multiplying the Net Supplemental Assessment by the tax rate, and then multiplying that amount by a monthly proration factor. The proration factors are shown below.

Tax Effective Proration Factor
January 1 0.50
February 1 0.42
March 1 0.33
April 1 0.25
May 1 0.17
June 1 0.08
July 1 1.00**
August 1 0.92
September 1 0.83
October 1 0.75
November 1 0.67
December 1 0.58

** A supplemental event that occurs in June rolls over to July 1, the first day of the new fiscal year. As a result, there is no supplemental assessment to the current roll; however, there is a supplemental assessment to the new main roll (the annual tax roll created on the January 1 Lien Date) that covers the full 12 months of the coming fiscal year. Therefore, a single supplemental bill or refund is issued.

Click on this link to estimate your supplemental taxes.