Your first-year supplemental property tax bill
A purchase resets the assessed value, and the supplemental bill is the catch-up between the old value and yours, charged on the difference and prorated from the first day of the month after you bought through the end of the fiscal year on June 30. Buy between January 1 and May 31 and there are two of them: one for the rest of that fiscal year and one for the whole of the next. Buy between June 1 and December 31 and there is generally one. It arrives separately from the annual bill, and it is the bill buyers are most often not expecting.
The LA County property tax estimator works out the amount if you can tell it what the property was assessed at before you bought, which is on the Assessor's parcel record and usually in the escrow file.
What it is, and what it is not
It is not a second annual bill and it is not a mistake. When you buy, the county resets the assessed value to what you paid, and the annual bill that was already issued for that fiscal year was calculated on the seller's value. The supplemental bill is the difference, charged only for the months of the fiscal year that were left after you bought.
So the figure is driven by how far the value moved, not by what the house cost. A buyer paying $1,200,000 for a property assessed at $1,150,000 owes very little. A buyer paying the same price for a property assessed at $300,000 since the 1990s owes a great deal, because the seller had been protected for thirty years: Prop 13 explained is why those two numbers were so far apart.
How the county works out the amount
A year's tax on the difference in value, multiplied by the share of the fiscal year the assessment covers. The assessment takes effect on the first day of the month after the purchase and the fiscal year ends on June 30, so a September purchase takes effect on October 1 and is charged for nine months of it. A June purchase takes effect on July 1, at the start of a fiscal year rather than the end of one, so its factor is a whole year.
Buy between January 1 and May 31 and there are two supplemental bills rather than one: the rest of that fiscal year, and the whole of the following one. The reason is the lien date. The roll for the coming fiscal year is based on ownership as of January 1, which is before your purchase, so the catch-up has to be made for that year as well.
| Month you bought | Takes effect | Share of a year's tax | Bills |
|---|---|---|---|
| January | February 1 | 0.42 | Two |
| February | March 1 | 0.33 | Two |
| March | April 1 | 0.25 | Two |
| April | May 1 | 0.17 | Two |
| May | June 1 | 0.08 | Two |
| June | July 1 | 1.00 | One |
| July | August 1 | 0.92 | One |
| August | September 1 | 0.83 | One |
| September | October 1 | 0.75 | One |
| October | November 1 | 0.67 | One |
| November | December 1 | 0.58 | One |
| December | January 1 | 0.50 | One |
LA County Property Tax Estimator
Estimates the annual property tax on an LA County property, including the homeowner's exemption and the supplemental bill a purchase triggers in the first year.
When it arrives, and why escrow does not cover it
Weeks to many months after the sale, depending on how long the Assessor takes to process the change of ownership and issue a new base year value. It comes as its own notice with its own due dates, and paying the annual bill does not settle it.
A lender's impound account is usually set up from the annual bill, so the supplemental often arrives as a demand nobody funded. If you have bought recently, the thing to do is set the money aside rather than wait to see whether a bill appears: a supplemental that has not arrived yet is a supplemental that has not been issued yet.
While you are dealing with the post from the purchase, the other thing to find is the exemption claim. The homeowner's exemption in LA County is the form nobody files for you, and it is worth about $87.50 every year you own the place.
If the number looks wrong
Check the new base year value on the notice against what you paid. The assessment is supposed to be the purchase price in an arm's length sale, and there is a formal route to disagree with the Assessor's value as well as a decline-in-value review if the market has moved since. The notice itself says how long you have to respond, which is short.
If you bought a property and also built on it, the new construction is assessed separately and can produce its own supplemental. When a property is reassessed covers which events do that.
Common questions
Why did I get a second property tax bill after buying?
I bought in March and received two supplemental bills.
Will my lender pay the supplemental bill from escrow?
Can I pay a supplemental bill in installments?
Related guides
- Prop 13 explained: what it caps, and what it does notProposition 13 caps the tax rate at 1% and limits how fast an assessed value can rise. What it does not cap, and what resets it.
- The homeowner's exemption in Los Angeles CountyThe $7,000 homeowner's exemption takes about $87.50 a year off the tax on a home you live in. Who qualifies, how to claim it, and how to tell whether you have it.
- When is a property reassessed in California?A change of ownership and completed new construction reset an assessed value. A refinance, a transfer between spouses and ordinary repairs generally do not. Each has conditions.
The figures on this page were last checked by a person on October 16, 2026