What Is a Supplemental Tax Bill and When Will It Hit My New El Segundo Rental?

Published July 15, 2026

A one time reassessment bill kicks in the first of the month after you close. Buy Jan through May and you get two of them.

A supplemental tax bill is a one time, separate charge the LA County Assessor issues when your purchase triggers a reassessment. California Revenue and Taxation Code section 75.10 requires the Assessor to reappraise the property to full cash value on the date ownership changes, and section 75.41 then prorates the supplemental assessment from the first day of the month following that change, not the next annual tax roll. If you close between January 1 and May 31, section 75.11 requires two separate supplemental assessments, meaning two bills. Expect the bill roughly four to six months after closing.

We get this question from almost every new owner buying their first South Bay rental, so it is worth walking through slowly.

Why the bill exists at all

California taxes real property on a base year value system under Proposition 13 (Cal. Const. art. XIII A). Your annual bill is built off the assessed value on the January 1 lien date, and that value normally only moves up to 2% a year. A sale breaks that cycle. When ownership changes, the Assessor must reappraise the property to full cash value as of the transfer date under Revenue and Taxation Code section 75.10. That new number almost always differs from what the seller was paying, especially if the seller had owned the property a long time. The gap between the old assessed value and your new purchase price based value gets billed separately as the supplemental assessment, prorated for the months remaining in that fiscal year (which runs July 1 to June 30 in California).

The two bill trap: January through May closings

This is the part that surprises owners. Revenue and Taxation Code section 75.11 splits a change in ownership that happens between January 1 and May 31 into two supplemental assessments. The first covers the remainder of the fiscal year the sale happened in. The second covers the entire following fiscal year, because the annual roll being prepared during that window is based on the assessor's lien date value, which has not yet caught up to your new purchase price. Close in June through December instead, and the annual roll catches up in time, so you typically get just one supplemental bill.

Either way, these bills come from the LA County Treasurer and Tax Collector separately from your regular annual property tax bill, and they are due on their own installment schedule with their own delinquency dates. Missing one carries the same 10% penalty structure as a regular secured bill.

How LA County actually mails it

The LA County Property Tax Portal notes that supplemental bills typically arrive around six months after the recorded transfer, sometimes longer if the Assessor's office is backed up. That lag catches buyers off guard because escrow does not collect this money at closing. Your lender's impound account, if you have one, is usually not sized to cover it either, since it is based on the seller's old tax bill at the time your loan was set up. Budget for it as a separate line item in your first year of ownership rather than assuming your monthly payment already covers it.

What this means for you

If you closed on a South Bay rental in the last year, do not assume a quiet mailbox means you are in the clear. Check the LA County Property Tax Portal directly using your parcel number rather than waiting for a bill that might already be late. Build the supplemental amount into your first year underwriting, not just the ongoing property tax line, especially if you bought from a long time owner whose assessed value was far below the sale price.

If you would rather not track assessor timelines yourself, that is one of the quieter things we handle for owners at Schofield.

This is general information, not legal or tax advice. Confirm with a licensed tax professional or the LA County Assessor before you act.

Sources

1. California Revenue and Taxation Code Section 75.10
2. California Revenue and Taxation Code Section 75.11
3. California Revenue and Taxation Code Section 75.41
4. LA County Property Tax Portal, Supplemental Secured Property Tax Bill
5. LA County Treasurer and Tax Collector, New Property Owner
6. California State Board of Equalization, Supplemental Assessment

Last verified: July 2026.

Topics: taxes, property tax, supplemental assessment, LA County, closing costs

Back to the Schofield Properties blog

Schofield Properties is a family run property management company at 323 Richmond St, El Segundo, CA 90245. We have managed the South Bay since 1972 and personally oversee about 186 doors today. Book a call to talk about your property.