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Supplemental Property Tax Calculator
California buyers get a surprise bill 6-18 months after closing: supplemental property tax covering the gap between old and new assessed values. This calculator sizes the first-year bill and the going-forward tax.
CA base 1% + locals ~0.1-0.5%
Supplemental bill (first year)
$2,013
Annual supplemental
$3,450
full year at new rate
New annual tax going forward
$7,878
Reassessment delta
$300,000
How the math works
California supplemental property tax is billed separately after a reassessment event (sale or new construction). It covers the difference between old and new assessed values for the portion of the year starting from the reassessment date.
Supplemental bills catch new homeowners off guard — they don't go into escrow and arrive 6-18 months after closing. Budget for it separately. Sometimes two supplemental bills arrive (one for prior fiscal year, one for current).
How to Use
- Enter new assessed value (usually purchase price under Prop 13).
- Enter old assessed value.
- Enter total tax rate (CA base 1% + local assessments).
- Enter month of reassessment (closing month).
Frequently Asked Questions
Why didn't escrow cover this?
Escrow is set at closing based on old assessed value. The supplemental bill covers the gap at new value for the partial year, plus often a second bill for the new fiscal year. Always arrives direct to homeowner, not through escrow.
When will I get the bill?
6-18 months after closing. Varies by county — busier counties are slower. Don't spend the expected supplemental funds until the bill arrives. Set aside proportionally so you're not surprised.
Is the supplemental bill deductible?
Yes — as part of property tax (subject to SALT cap). Payable across one or two installments depending on when the bill arrives relative to the tax year.
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