Supplemental Property Tax and Due Dates: What Every New Homeowner in California Should Know
- The tax year is July 1 – June 30. Values are set as of January 1 each year.
- First half: due Nov 1, late after Dec 10. Second half: due Feb 1, late after April 10. You can pay both at once by Dec 10.
- Buy between June 1 and Dec 31: usually one supplemental bill. Buy between Jan 1 and May 31: usually two.
- Most buyers receive a supplemental bill, because the purchase price is usually higher than the previous owner’s assessed value.
- Supplemental bills go to you, not your lender, so set money aside.
Almost every buyer I work with is surprised by this one. A few months after closing, an extra property tax bill shows up, sometimes for several thousand dollars. It is not a mistake. It is the supplemental tax, and in most cases, if you buy a home, there is a very good chance you will receive one. Under Prop 13, the previous owner’s assessed value usually grew by no more than 2% a year, so it is often well below what you paid, especially if they owned the home for a long time. That gap is what the supplemental bill covers, and once you understand how the property tax calendar works, it makes sense and you can plan for it.
The property tax calendar
- Tax year: July 1 through June 30.
- Value date (lien date): January 1. The value on January 1 is what the regular bill for the next July–June year is based on.
- Bills mailed: usually in October.
- First installment: due November 1, delinquent after December 10.
- Second installment: due February 1, delinquent after April 10.
- Pay it all at once: you can pay both installments together by December 10.
- Late penalties: 10% on a late installment, plus a small cost charge on a late second installment. If a deadline falls on a weekend or holiday, you have until the next business day.
Didn’t get a bill? You still owe it, and not receiving a bill does not excuse late penalties. Look it up by address on your county Treasurer-Tax Collector’s website. In Alameda County that is the Alameda County property tax portal. If your taxes are paid through your lender’s impound account, confirm the lender paid it.
What is a supplemental tax bill?
When a home changes ownership (or new construction is completed), the Assessor re-values it at the purchase price as of that date. But the regular bill for the year was already set using the previous owner’s value. The supplemental bill makes up the difference.
Supplemental tax = (your purchase price − the previous assessed value) × the tax rate × the portion of the tax year remaining
Only the percentage rate (the 1% plus voter-approved bonds) applies. Fixed charges like Mello-Roos and parcel taxes are already on the regular bill. The new value takes effect on the first day of the month after you close, and the bill is prorated from then through June 30.
One bill or two? It depends on when you close
- Close between June 1 and December 31: usually one supplemental bill, covering the rest of the current tax year. The next regular bill will already reflect your new value.
- Close between January 1 and May 31: usually two supplemental bills. One covers the rest of the current tax year. The second covers the entire next tax year, because that year’s regular bill was based on the January 1 value, which was still the old one.
Two examples
Both assume the previous assessed value was $600,000, you paid $1,200,000, and the tax rate is 1.17% (illustrative). The yearly difference is $600,000 × 1.17% = $7,020.
| Close in August | Close in March | |
|---|---|---|
| New value takes effect | September 1 | April 1 |
| Months left in tax year | 10 (factor 0.83) | 3 (factor 0.25) |
| First supplemental bill | about $5,830 | about $1,755 |
| Second supplemental bill | none | about $7,020 (full next year) |
Paid less than the old value? You may get a refund
If your purchase price is lower than the previous assessed value, the supplemental assessment is negative and the county issues a refund instead of a bill. The refund is not a credit against your regular bill, so keep paying that on time.
Who pays it, and when?
- It comes to you, not your lender. Lenders do not receive supplemental bills, so even if your regular taxes are impounded, you usually pay this one yourself. Ask your lender if they want to handle it.
- It can take months to arrive, often several months after closing. The due dates are printed on the bill and depend on when it is mailed.
- Escrow does not prorate it. Escrow splits the regular bill between buyer and seller, but the supplemental bill is the new owner’s.
- File the Homeowners’ Exemption if you live in the home. It also applies to supplemental assessments.
Estimate yours before you close
Alameda County has an official Supplemental Tax Estimator: enter the purchase date, price and current roll value. To estimate your regular yearly tax, see how to estimate property tax on a home you are buying.
Quick answers
When is property tax due in California?
The first installment is due November 1 and becomes delinquent after December 10. The second is due February 1 and becomes delinquent after April 10. You can pay both together by December 10.
What is a supplemental property tax bill?
A bill sent after a change of ownership or new construction for the difference between the new value and the previous assessed value, prorated from the first of the month after the event through June 30.
Why did I get two supplemental tax bills?
If you bought between January 1 and May 31, the next year’s regular bill was based on the old January 1 value, so a second supplemental bill covers that full year.
Does my lender pay the supplemental tax bill?
Usually not. Supplemental bills are sent to the owner, not the lender. Pay it yourself or confirm with your lender who will pay it.
Can a supplemental assessment result in a refund?
Yes. If you bought for less than the previous assessed value, the county issues a refund instead of a bill.
Want to know what to set aside? Send me the address and your expected closing date, and I'll estimate your supplemental bill and your regular yearly tax.
Bilal Salimi, Broker · Visionary Estates · CA DRE #01480904
Insights are general information to help you think through your options. They aren't legal, tax or financial advice, and every situation is different. Visionary Estates · 44840 S Grimmer Blvd, Fremont, CA 94538 · CA DRE #01480904 · Equal Housing Opportunity.