A supplemental assessment is a mid-year or after-sale extra bill when value changes. The regular roll often still shows the old figure until next cycle.
A supplemental property tax assessment is California's mid-year or after-sale extra bill that captures a value change the regular roll has not caught yet. Not every state issues one. A purchase is the usual trigger. New construction can be another. The extra invoice covers the gap until the next regular roll.
What is a supplemental assessment after buying a house?
California's Board of Equalization describes a supplemental assessment as the difference between the property's new value after a change in ownership or completed new construction and the value already on the roll. Other states use different stamps for the same mid-year catch-up. The regular January cycle is not the only time a new number can produce a bill.
Example: the roll still says $200,000, the sale resets value to $250,000, and 10 mills on the $50,000 gap is $500 for a full leftover year. That pairing is an example, not one county's 2026 invoice.
Look up if you are overpaying.
Is a supplemental assessment the same as the yearly property tax bill?
No. The yearly bill follows the regular roll. A supplemental bill is the extra slice for a value change that arrived in between. A property tax appeal, when one is filed, is still aimed at a printed value, including a new one on a supplemental notice. The property tax glossary keeps the regular roll next to the mid-year catch-up. You pay only if FairAppeal saves you money, and there are no upfront costs with Fair Appeal.
Frequently asked questions
- What is a supplemental property tax assessment?
- A supplemental property tax assessment is a mid-year or after-sale extra bill that captures a value change the regular roll has not caught yet. A purchase is a common trigger. New construction can be another. The extra invoice covers the gap until the next regular cycle.
- Why did I get a supplemental tax bill after buying a house?
- A purchase often resets the value the county uses, while the regular roll still carries the prior figure. The supplemental bill charges the difference for the rest of that tax year. California's Board of Equalization describes that gap as the new value minus the old roll value.
- Is a supplemental assessment the same as a property tax appeal?
- A supplemental assessment is not an appeal. It is an extra bill from a mid-year value change. A property tax appeal is a later request that a printed value come down. The supplemental notice can still carry the number a later filing would target.