California Property Taxes & Mortgages: Proposition 13 and Supplemental Bills
How Proposition 13 Governs California Mortgages
Under California Proposition 13 (passed in 1978), the ad valorem base tax rate is constitutionally capped at 1% of the assessed purchase price. In addition, voter-approved local school, sewer, and infrastructure bond measures typically add 0.15% to 0.35%, yielding an average total ad valorem rate of 1.15% to 1.35% across most California counties.
Equally critical: Prop 13 restricts subsequent annual increases in taxable assessed value to the California Consumer Price Index (CPI) or a strict maximum of 2% per year, as long as ownership does not change.
Beware the Surprise Supplemental Property Tax Bill
A frequent shock for new California homeowners is the Supplemental Property Tax Bill. When you purchase a property, county appraisers immediately reassess the home from the seller old Prop 13 base to your new purchase price. However, your lender escrow department often pays the previous owner lower assessment during the transition year.
The county tax collector sends the difference directly to you as an unescrowed supplemental bill. If you don't budget cash reserves to pay it, or notify your servicer to disburse funds from escrow, penalties can accumulate quickly.
Sample California Tax & Escrow Breakdown on $850,000 Purchase
| Component | Assessment Rate | Annual Amount | Monthly Escrow |
|---|---|---|---|
| Prop 13 Base Tax (County) | 1.000% | $8,500.00 | $708.33 |
| Local Voter Bonds & Levies | 0.225% | $1,912.50 | $159.38 |
| Mello-Roos (Community District) | Fixed Special Tax | $2,100.00 | $175.00 |
| Total California Property Tax | Effective ~1.47% | $12,512.50 | $1,042.71/mo |
Frequently Asked Questions
What is Mello-Roos and does it affect mortgage approval?
Mello-Roos is a special tax parcel assessment created under the Community Facilities Act to finance infrastructure (schools, parks, roads) in newer master-planned communities. Lenders treat Mello-Roos as a mandatory monthly housing expense in your front-end DTI.
Does my mortgage escrow cover the supplemental tax bill?
Typically no. County treasurers mail supplemental bills directly to the property address. You must either pay the county directly from personal savings or submit the billing statement to your mortgage servicer to request an escrow disbursement.