California Property Tax Calculator
Understand your current California property tax — or estimate what it could become after you buy — using official Proposition 13 inflation factors.
Uses official California Proposition 13 inflation factors and transparent calculation methods. Free to use, no account required.
Property tax estimates for current owners and buyers
California property taxes require different calculations depending on whether you already own the property or are considering purchasing it. Current owners can estimate how an earlier acquisition value may have changed under Proposition 13. Buyers can estimate the property taxes that may apply after a new purchase establishes a new assessed value. Choose the mode that matches your situation.
Current owners
Use your original purchase price and acquisition date to estimate your current assessed value using California's historical Proposition 13 factors.
Prospective buyers
Use your expected purchase price and purchase date to estimate the property taxes that may apply after purchase.
Learn how California property taxes differ for owners and buyers
Why This California Property Tax Calculator Is Different
Many property tax calculators ask only for a home's current value and county. That approach can be misleading in California because Proposition 13 generally bases taxable value on a property's acquisition value, not its current market value.
California Property Tools starts with the property's purchase price and purchase date. It then applies California's official historical Proposition 13 inflation factors year by year to estimate the property's current factored base-year value. A county-level estimated tax rate is then applied to produce an estimated annual and monthly property tax.
This provides a more useful estimate for existing California homeowners whose assessed values may be substantially lower than their homes' current market values.
Purchase-history based
Starts with the price and date the property was acquired.
Official inflation factors
Applies California's published annual Proposition 13 factors instead of assuming exactly 2% every year.
Transparent calculation
Shows the estimated assessed-value history and explains the assumptions behind the result.
How California Property Taxes Are Estimated
Step 1: Establish the starting base-year value
A property purchase commonly establishes a new base-year value. For this calculator, the purchase price is used as the estimated starting base-year value.
Step 2: Apply Proposition 13 inflation factors
Proposition 13 generally limits annual increases in a property's factored base-year value to the California inflation factor, capped at 2%. The factor is sometimes lower than 2%, so the calculator applies the official historical factor for each applicable assessment year.
Step 3: Estimate the current factored base-year value
The purchase price is compounded using the applicable annual factors to estimate the property's current Proposition 13 factored base-year value.
Step 4: Apply the county-level tax rate
The estimated assessed value is multiplied by a county-level estimated property tax rate. This produces an estimated annual property tax and monthly equivalent.
- Purchase price and date
- Historical Prop. 13 factors
- Estimated factored base-year value
- County-level estimated tax rate
- Estimated annual and monthly tax
Assessed Value Is Not the Same as Market Value
A home's market value is the amount it might sell for today. Its assessed value is the value used by the county to calculate value-based property taxes.
Under Proposition 13, an existing owner's assessed value may be much lower than the property's current market value. A home purchased many years ago can therefore have a significantly lower property tax bill than a similar home purchased recently.
This calculator estimates the normal Proposition 13 assessment path. It does not estimate the home's current market value.
What This Estimate Does Not Include
California property tax bills can contain parcel-specific taxes and assessments that cannot be determined from purchase price, purchase date, and county alone.
Mello-Roos special taxes
Charges associated with certain Community Facilities Districts, often found in newer developments.
Parcel taxes and special assessments
Fixed or formula-based charges for schools, lighting, landscaping, sewer, flood control, and other local services.
Exact Tax Rate Area rates
Voter-approved debt rates can vary within the same county based on the property's Tax Rate Area.
Supplemental assessments
Additional bills that may be issued after a purchase or completed new construction.
Proposition 8 reductions
Temporary reductions when a property's market value falls below its normal Proposition 13 factored value.
Later assessment events
New construction, partial ownership changes, base-year-value transfers, escape assessments, disaster relief, or assessor corrections.
The result is an educational estimate and should not be treated as an official county assessment or tax bill.
Who Can Use This Calculator?
This calculator is designed for California homeowners, buyers, real estate investors, agents, and anyone trying to understand how purchase history affects property taxes under Proposition 13.
Existing homeowners
Estimate how a property's assessed value may have changed since purchase.
Prospective buyers
Estimate taxes using an expected purchase price and county.
Real estate investors
Compare likely property-tax costs across California counties.
Agents and advisers
Explain why a seller's current tax bill may differ from a buyer's future bill.
Frequently Asked Questions
- What does this calculator estimate?
- It estimates a property's Proposition 13 factored base-year value using its purchase price, purchase date, and California's official historical inflation factors. It then applies a county-level estimated tax rate to calculate annual and monthly property tax.
- Is this the county's official assessed value?
- No. It is an estimate of the property's normal Proposition 13 assessment path. The county's official enrolled value may differ because of Proposition 8 reductions, new construction, ownership changes, exemptions, transferred base-year values, escape assessments, disaster relief, or corrections.
- Why do you ask for the purchase date?
- The purchase date helps determine when the new base-year value was established and which annual Proposition 13 inflation factors apply.
- Why is the annual increase not always exactly 2%?
- Proposition 13 caps the annual inflation adjustment at 2%, but the actual California inflation factor can be lower. The calculator uses the official historical factor for each year instead of automatically applying 2%.
- Does the calculator use current market value?
- No. The main estimate is based on the property's purchase history. Current market value does not ordinarily replace the Proposition 13 factored base-year value unless a reassessment event occurs or a temporary Proposition 8 reduction applies.
- Does this include Mello-Roos?
- No. Mello-Roos is parcel-specific and cannot be determined accurately from county and purchase history alone.
- Why might my actual tax bill be higher?
- Your bill may include Mello-Roos, parcel taxes, special assessments, or Tax Rate Area bond rates that are not fully reflected in the county-level estimate.
- Why might my official assessed value be lower?
- The property may have received a temporary Proposition 8 decline-in-value reduction because its market value fell below its normal Proposition 13 factored value.
- Can the assessed value increase by more than 2%?
- Yes, in some circumstances. For example, a Proposition 8 value can rise by more than 2% as market value recovers, although it generally cannot exceed the normal Proposition 13 factored base-year value without another reassessment event.
- Is the purchase price always the official base-year value?
- Not always. The purchase price is usually strong evidence of market value, but the county assessor determines the official base-year value.
Methodology and Data Sources
The calculator uses publicly available California property-tax rules and historical inflation data. The core estimate starts with the user-entered purchase price, applies the official annual Proposition 13 inflation factors for the applicable assessment years, and multiplies the resulting estimated factored base-year value by a county-level estimated tax rate.
County rates are estimates and may not represent the exact rate for a specific Tax Rate Area or parcel. Parcel-specific direct charges are not included unless explicitly stated.
Read the full methodology, data sources, and historical Proposition 13 factors. See also About and our Privacy Policy.
Inflation factors cover assessment years through 2026-27. Last reviewed: August 2026.