Contra Costa County, CA — Property Tax Underwriting Guide
California · Prop 13 event-driven
What this means for multifamily underwriting
On acquisition, underwrite taxes to approximately purchase price x (1% + local bond rate). The seller's Prop 13 base-year value is not a sustainable post-sale run-rate.
Transaction type breakdown
Change of ownership triggers reassessment to current market value under Prop 13. Entity transfers of more than 50% control also qualify.
A refinance with no change of ownership is not a reassessment event; the existing Prop 13 base-year value carries forward.
A change in ownership or control is the trigger; the property is reassessed to fair market value as of the transfer date and a new Prop 13 base-year value is set.
Tax appeal information
Effective rate varies by Tax Rate Area (local voter-approved bonds); confirm the parcel's TRA and any Mello-Roos / special assessments.
Guide review
County guidance last reviewed: July 17, 2026
Tax-rate scope: County-level underwriting placeholder; not a parcel-specific tax rate.
Official sources: Contra Costa County Assessor, CA State Board of Equalization - County Contacts
California Prop 13 framework and Contra Costa County assessor source reviewed 2026-07-17. The 12.8-mill rate is a county-level representative placeholder; confirm the parcel's Tax Rate Area, voter-approved debt, and special assessments.
Sources
Parclio estimates are underwriting guidance, not legal or tax advice. Always verify millage rates, the seller's assessed value, and appeal deadlines with the county assessor or local counsel before relying on these numbers for a credit decision.
Run a tax reset estimate for Contra Costa County
Use Parclio's estimator to model the post-closing tax bill, NOI impact, DSCR change, and underwriting memo language for your next Contra Costa County deal.