Your First Property Tax Bills After Buying a Bay Area Home

How is property tax set after you buy?

Under Proposition 13, the owner on January 1 each year owes a tax of 1% of the property's taxable value, plus a rate for voter-approved debt that differs by area (Board of Equalization Publication 29). A purchase is a change in ownership, so the county assessor resets the value to the market value on the date of the purchase. That becomes your base year value (Revenue and Taxation Code 110.1, 75.10).

Each later year, the base year value can rise with inflation by no more than 2% (Revenue and Taxation Code 51). For the 2026-27 tax year the Board told assessors to use the full 2% factor, 1.02 (Letter To Assessors No. 2026/002, January 13, 2026). If the market value on January 1 falls below that factored value, the lower market value is taxed instead, which counties often call a Proposition 8 review.

The practical point for a buyer: the seller's tax bill is not your tax bill. A seller who bought long ago may have a much lower assessed value, and your purchase price replaces it.

What rate will I pay?

The rate is 1% plus the debt rates for the tax rate area the home is in, so it differs within a county. The table shows the Board's 2024-25 county averages and the most recent published figures from three counties.

• Your bill also lists direct charges, such as sewer, parcel taxes, lighting districts or a Mello-Roos special tax. These are flat or formula amounts, not a percentage of value, so read the direct charges section of each bill. For a Mello-Roos tax, the seller is required to try to get the district's notice for you (Civil Code 1102.6b).
• Your county's rate book lists the rate for each tax rate area.

What is the supplemental tax bill?

The annual bill for each tax year is based on the value on January 1. When a home sells during the year, the county catches up with a supplemental assessment: the new value minus the prior assessed value. If the difference is positive, you get a supplemental bill; if it is negative, a refund (Board of Equalization, Supplemental Assessments page). A refund does not reduce what is still due on the annual bill.

The bill covers the months from the first day of the month after your purchase through June 30, the end of the tax year. A purchase from June 1 through December 31 produces one supplemental bill. A June purchase rolls over to July 1, so its one bill covers the whole next tax year (Board of Equalization, Supplemental Assessments page). A purchase from January 1 through May 31 produces two: one for the rest of the current tax year, and one for the full next tax year, because that year's roll was set on January 1, before you bought (Revenue and Taxation Code 75.11).

The county computes it as the net supplemental value times the tax rate, times the share of the year that remains:

What does that look like in numbers?

A hypothetical example, with amounts invented for arithmetic only as of November 7, 2026, and an illustrative rate of 1.2%. You buy for $1,200,000. The seller's assessed value was $450,000, so the net supplemental value is $750,000, and a full year's tax on it is $9,000.

If you close on October 10, 2026, the change takes effect November 1, so the supplemental bill is $9,000 × 0.67 = $6,030. That is the only supplemental bill; the 2027-28 annual bill will already use your new value, if the assessor has finished your reassessment by then.

If you close on March 10, 2027 instead, the change takes effect April 1. The first supplemental bill is $9,000 × 0.25 = $2,250 for the rest of 2026-27. A second covers all of 2027-28, about $9,000, because the 2027-28 roll was set on January 1, 2027 at the seller's value. You still get the 2027-28 annual bill at the seller's value; that annual bill and the second supplemental bill together come to about a full year's tax on your price, not more (Board of Equalization, Supplemental Assessments page). Your own bill uses your county's actual rates and values.

When does the supplemental bill come, and who pays it?

First the assessor mails a Notice of Supplemental Assessment showing the new value, the prior value and the event date. The bill follows from the tax collector. You generally have 60 days from the notice's mailing date to appeal the value. In Los Angeles County and any county whose board of supervisors has adopted an alternative resolution, the 60 days run from the mailing date printed on the tax bill or its postmark, whichever is later (Publication 29).

Timing differs by county, and the bill often comes long after closing:

• Alameda: the Assessor says there is no statutory timeline and most bills are mailed within 12 months after a change in ownership.
• Contra Costa: the Auditor-Controller says bills are generated about 60 days after the date on your notice.
• San Francisco: the Assessor says the Treasurer mails the bill within 60 days of the notice, but its current timeline for most sales and other assessable events is about two years. Until then, annual bills may keep the old value, and the difference comes later as supplemental and escape assessments (an escape assessment corrects a past year's value), which the Assessor says do not add to what you would have owed on time.
• San Mateo: the Tax Collector says most bills are mailed within nine months, and its new homeowner sheet says bills typically arrive 6 to 9 months after purchase but may take longer.
• Santa Clara: the Assessor mails a notice to the owner before the bill is issued.

When is a supplemental bill due?

It depends on when it is mailed (Publication 29). A bill mailed from July 1 through October 31 is due on the same dates as the annual bill: delinquent December 10 and April 10. A bill mailed from November 1 through June 30 has its first installment delinquent on the last day of the month after the month it was mailed, and its second installment delinquent on the last day of the fourth month after that.

Contra Costa, San Francisco and San Mateo apply the same 10% late penalties as on the annual bill. And an unpaid supplemental bill can put the whole property into tax default even when the annual bill is paid (Publication 29).

What about the annual bill in my first year?

Annual secured bills are mailed by November 1. The first installment is due November 1 and delinquent after December 10; the second is due February 1 and delinquent after April 10. Each late installment adds a 10% penalty, and counties add a small cost on the second (Publication 29; county tax collectors).

In your first year, the annual bill may still be in the seller's name or mailed to the seller. Contra Costa says that taxes prorated in escrow may not yet have been paid to the Tax Collector, that "It is your responsibility to obtain the bill," and that not receiving one does not excuse penalties. San Mateo says you must pay it even if it is in the previous owner's name, if you own the property when taxes are due.

If your lender pays from an impound account, Contra Costa says you should receive a copy marked "INFORMATION COPY". A bill without that mark, or one tied to the seller's lender, is a reason to call your loan servicer right away.

How do I get the homeowners' exemption?

If the home is your principal residence on January 1, the homeowners' exemption takes $7,000 off its assessed value. At a 1% rate that saves about $70 a year; at 1.17%, $82 (Board of Equalization Publication 800-6). It does not apply to a home that is rented, vacant, under construction on January 1, or a vacation or second home.

You file form BOE-266 once with the county assessor; it stays in place until you no longer qualify. Contra Costa, San Francisco and San Mateo say they mail the form to new owners; if it has not come within a few months, ask the assessor for one.

• Full exemption: file by February 15 for the tax year starting July 1.
• Late: file February 16 through December 10 for 80%, or $5,600. Nothing for that year after December 10.
• On a supplemental bill: if you bought after January 1, moved in within 90 days, and the seller did not have the exemption, file within 30 days of the date on the Notice of Supplemental Assessment for the full amount, or by the first installment's delinquency date on the supplemental bill for 80%.
• If you later move out or rent the home, tell the assessor. December 10 is the last day to end the exemption without penalty.

What paperwork goes to the county?

The buyer signs a Preliminary Change of Ownership Report, form BOE-502-A, which normally goes in with the deed at recording. If it does not, the recorder may charge an extra $20 (Revenue and Taxation Code 480.3).

If the report is not filed when the deed is recorded, the buyer must file a Change in Ownership Statement within 90 days of the transfer (480). There is no penalty for missing those 90 days alone: the penalty applies only if you do not file within 90 days after the assessor mails a written request. It is $100 or 10% of the tax on the new base year value, whichever is greater, up to $5,000 if the home qualifies for the homeowners' exemption or $20,000 if not, unless the failure was willful (482; Board of Equalization, Change in Ownership FAQs).

I am 55 or older and sold my last home. Can I keep its tax base?

Possibly. Under Proposition 19, a homeowner who is 55 or older, severely and permanently disabled, or a victim of a wildfire or natural disaster can transfer the taxable value of a principal residence to a replacement anywhere in California, bought within two years before or after selling the original (Revenue and Taxation Code 69.6). Owners who qualify by age or disability can do this up to three times.

The replacement's market value is compared with the original's: up to 100% if you buy first, 105% if you buy within the first year after the sale, and 110% in the second year. Any value above that limit is added to the transferred value. You file the claim with the assessor of the new home's county within three years of buying it; the Board says this "is not done through escrow." If you buy the replacement first, you pay tax on its full market value until the original sells, with no refund for that period.

What should I do after closing?

• Keep your closing statement and note how the current year's taxes were prorated and whether the seller's installment was paid.
• Look up your parcel on the county tax collector's site and check who the annual bill is addressed to.
• Ask your loan servicer which bills it pays, and set money aside for the supplemental bill.
• File the homeowners' exemption as soon as the form arrives, and watch for the Notice of Supplemental Assessment: if the seller did not have the exemption, its 30-day window decides whether you get the full amount.
• Check the value on the notice; you generally have 60 days from its mailing date to appeal.
• Pay any supplemental bill yourself by its own due dates, unless your servicer confirms in writing that it will.

The short version

A purchase resets your property's assessed value to what you paid, and your tax becomes about 1% of it plus local debt rates. Because the annual bill was already set, the county sends one supplemental bill if you buy from June through December, or two if you buy from January through May. Plan to pay those yourself, since four Bay Area counties say impound accounts generally do not cover them, and, if the home is your principal residence, file the homeowners' exemption to take $7,000 off your value.

Every rule above was checked against the Board of Equalization or the county's own page on November 7, 2026. This is general education, not tax or legal advice. For your own bill, ask the county assessor or tax collector, and confirm tax planning with your CPA.

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