A supplemental tax bill is an extra property tax bill California homeowners receive after buying a home or completing new construction. It covers the difference between the previous owner's assessed value and your new assessed value for the remainder of the tax year.
This catches many new California homeowners off guard. You budget for the regular property tax bill, then receive one or two supplemental bills totaling thousands of dollars.
Supplemental bills exist because California reassesses property to market value upon sale. If you bought a home that was previously assessed at $300,000 for $600,000, you owe the tax difference for the months remaining in the fiscal year.
Supplemental bills surprise California homebuyers who only budgeted for the disclosed property tax amount. They can arrive 6-12 months after purchase, just when you've forgotten about them.
The good news: You can appeal supplemental assessments too. If you believe your purchase price overstated market value (divorce sale, estate sale, or market decline since purchase), you can file an Assessment Appeal Application within 60 days of the supplemental notice.
Plan ahead. When buying in California, ask your agent or escrow company to estimate your supplemental tax bill so you're not caught off guard.
You purchase a home in October for $700,000. The previous owner's assessed value was $350,000 (they owned since 2005).
The reassessment adds $350,000 to the tax rolls. For the remaining 9 months of the fiscal year (October through June), you owe supplemental taxes on that increase:
Increase: $700,000 - $350,000 = $350,000
Tax rate: 1.1%
Annual tax on increase: $3,850
Prorated (9 months): $2,888
You'll receive this as a separate supplemental bill—on top of your regular property taxes.
Typically one or two. If your purchase spans two fiscal years (California's fiscal year runs July 1 to June 30), you may receive a supplemental bill for each year affected.
Usually 3-6 months after purchase or completion of construction. They can arrive up to a year later in some counties due to processing backlogs.
Yes. You have 60 days from the supplemental assessment notice to file an Assessment Appeal Application. If your purchase price doesn't reflect market value (estate sale, divorce, etc.), you may have grounds for reduction.