Understanding the San Diego Supplemental Property Tax Bill

When you buy a property in San Diego County, there is one additional tax bill you should be aware of after closing, the Supplemental Property Tax Bill. This is a standard part of California property ownership and applies any time a property changes ownership or new construction is completed.

Knowing what this bill is, why it exists, and when it shows up helps you plan ahead and avoid confusion later.

What Is a Supplemental Property Tax Bill?

California law requires counties to reassess a property whenever it is sold or newly constructed. Since property taxes are based on assessed value, a new assessment often changes the amount of tax owed.

A Supplemental Property Tax Bill is issued to account for the difference between:

• The property’s prior assessed value, what the previous owner was taxed on

• The new assessed value, typically based on your purchase price or current market value

The bill only covers the portion of the fiscal year that you own the property. The fiscal year runs from July 1 through June 30.

This supplemental bill is separate from your regular annual property tax bill, which is issued each October.

Why Supplemental Tax Bills Exist

At closing, property taxes are prorated based on the seller’s existing tax bill. The county cannot issue an updated tax bill until the sale is recorded and the reassessment is completed.

Once reassessment is finalized:

• The County Assessor updates the property value

• The County Treasurer-Tax Collector calculates the adjusted tax amount

• A Supplemental Property Tax Bill is mailed to the property owner

Because of this process, the bill often arrives weeks or months after closing.

How Is a Supplemental Property Tax Bill Calculated?

The calculation follows a straightforward process.

First, the county determines the new assessed value of the property, usually the purchase price. Next, it subtracts the prior assessed value. You are taxed only on that difference.

That amount is then prorated based on how many months remain in the fiscal year after you close. Finally, the standard property tax rate is applied.

Example

• Purchase price: $800,000

• Prior assessed value: $500,000

• Difference: $300,000

If you closed halfway through the fiscal year and your prorated portion is 50 percent, you would be taxed on $150,000. At an approximate 1 percent tax rate, the supplemental bill would be around $1,500.

This example is simplified, but it illustrates how the bill is determined.

When Will You Receive the Bill?

After the deed is recorded, the San Diego County Assessor begins the reassessment process. This can take several months, and in some cases up to a year.

Once reassessment is complete, the San Diego County Treasurer-Tax Collector issues the Supplemental Property Tax Bill.

The bill may be due in one or two installments, or paid in full by the first due date. Due dates vary, so it is important to review the bill carefully when it arrives.

Will Your Lender Pay the Supplemental Bill?

Supplemental Property Tax Bills are separate from annual property tax bills. Some lenders do not pay these through impound or escrow accounts, which is why the bill is usually mailed directly to the homeowner.

Once you receive it, you can contact your lender to confirm whether they will pay it or if you should handle payment directly.

Will You Receive This Bill Every Year?

No.

Supplemental Property Tax Bills are only issued when a qualifying event triggers a reassessment, such as:

• Purchasing or selling a property

• Completing new construction

• Adding or removing someone from the property title

In years without a qualifying event, you will only receive your regular annual property tax bill.

What Does a San Diego Supplemental Property Tax Bill Look Like?

Here is an example of what a San Diego County Supplemental Property Tax Bill typically looks like so you know what to watch for in the mail:

 

These bills often reference reassessed value, base year value, or supplemental secured property tax.

Official San Diego County Resource

For detailed information straight from the county, you can review the official San Diego County Treasurer-Tax Collector page here:
https://www.sdttc.com/content/ttc/en/tax-collection/supplemental-taxes.html

Final Thoughts

The Supplemental Property Tax Bill is a normal part of buying property in San Diego. It does not replace your annual tax bill and it is not a penalty. It simply reflects the updated value of your home after a change in ownership.

If you are buying, selling, or investing in San Diego and want an estimate of what this bill may look like before it arrives, this is something I review with my clients so everything stays clear and predictable.