Supplemental property tax calculator
New San Diego County owners receive a separate property tax bill after closing, and the Treasurer-Tax Collector mails it only to the owner.
Buyers fill the supplemental property tax calculator from the escrow statement and the seller's last annual bill.
Estimated supplemental tax
Estimate only, before any homeowners' exemption.
Value, rate and proration in the supplemental property tax calculator
The County Auditor and Controller multiplies the value change by the tax rate, then prorates it by the months left in the July to June fiscal year.
- Value change. The County Assessor subtracts the seller's assessed value from the purchase price, or values the new construction alone.
- Tax rate. The County Auditor applies the parcel's full rate, 1.16729% on average in 2025-26. Owners compare areas under San Diego property tax rate.
- Proration. The County Auditor starts the tax on the first day of the month after the event, using the State Board of Equalization proration table.
| Month of closing or completion | Share of the year billed |
|---|---|
| July | 0.92 |
| August | 0.83 |
| September | 0.75 |
| October | 0.67 |
| November | 0.58 |
| December | 0.50 |
| January | 0.42 |
| February | 0.33 |
| March | 0.25 |
| April | 0.17 |
| May | 0.08 |
| June | 1.00, for the next fiscal year |
Buyers moving in within 90 days can claim the homeowners' exemption on the supplemental if the seller had none. Owners filing within 30 days of the notice get the full exemption.
The Assessor issues no supplemental assessment after a transfer it doesn't reassess, such as a move into a living trust or a qualifying parent-child transfer. Heirs find the parent-child rules under California property tax inheritance.
Two supplemental bills for a January to May closing
After a January to May closing, the San Diego County Treasurer-Tax Collector mails two bills: one to June 30, one for the next full fiscal year.
The County Assessor sets values for the next annual bill on the January 1 lien date, before the sale. The Treasurer-Tax Collector bases that bill on the seller's value.
Supplemental tax example for a March closing
A buyer closes on a $900,000 Chula Vista condo in March 2027 over a $520,000 seller's assessed value, at the 2025-26 County average of 1.16729%:
- Value change: $900,000 − $520,000 = $380,000
- Full-year tax: $380,000 × 1.16729% = $4,435.70
- 2026-27 bill: $4,435.70 × 0.25 = $1,108.93
- 2027-28 bill, on the same value change and rate: $4,435.70 × 1.00 = $4,435.70
- Both bills together: $1,108.93 + $4,435.70 = $5,544.63
For the regular yearly bill, buyers use the San Diego property tax calculator.