California Mortgage Calculator (with California Property Taxes & Insurance)

California property tax is governed by Proposition 13, which caps the general tax rate at 1% of a property's assessed value and limits how fast that assessed value can grow, generally no more than 2% per year, until the property changes ownership and is reassessed at current market value. Because so many California homeowners have owned their properties for years under that 2% annual cap, the statewide average effective property tax rate, actual tax paid divided by current market value, runs meaningfully below the 1% statutory base rate. This calculator uses 0.73% as an effective-rate planning estimate applied to the purchase price, which reflects that a new buyer's first-year assessed value will typically equal the purchase price, close to the 1% base, once voter-approved local add-ons like school bonds are layered on.

Those local add-ons matter. On top of the 1% Prop 13 base, California allows voter-approved general obligation bond debt service and, in many newer developments, Mello-Roos Community Facilities District special taxes that fund infrastructure like roads, schools, and utilities in a specific subdivision. Mello-Roos assessments are not tied to Prop 13's cap and can add a noticeable amount to a property tax bill, sometimes 0.2% to over 1% of home value depending on the district, which is why two nearly identical homes in different California subdivisions can carry very different effective tax burdens.

This tool combines a standard 30-year fixed amortization for principal and interest with the modeled property tax rate and a flat homeowners insurance estimate to produce a single PITI figure, intended as an initial affordability check before a buyer requests a formal Loan Estimate from a California-licensed lender.

1. Down payment and loan principal. Loan Principal = Home Price x (1 - Down Payment %).
2. Principal and interest. The loan principal amortizes over 360 months:

$$PMT = \frac{P \times i}{1 - (1+i)^{-360}}$$

where P is the loan principal and i is the monthly rate (APR / 12).

1. Property tax estimate. Monthly Property Tax = Home Price x 0.73% / 12, using the purchase price as a proxy for the first-year Prop 13 assessed value.
2. Insurance estimate. A flat $125/month is added as a homeowners insurance placeholder.
3. PITI total. Monthly PITI = Principal & Interest + Property Tax + Insurance.

Using the calculator's baseline inputs, which match its published test vector:

• Home Purchase Price: $380,000
• Down Payment: 20% ($76,000)
• Interest Rate (APR): 6.5%

Step by step: - Loan principal: $380,000 x 80% = $304,000.00 - Monthly rate: 6.5% / 12 = 0.541667% - Monthly principal & interest: $1,921.49 - Monthly property tax: $380,000 x 0.73% / 12 = $231.17 - Monthly insurance estimate: $125.00 - Total monthly payment (PITI): $1,921.49 + $231.17 + $125.00 = $2,277.66 - Total interest paid over 30 years: $387,735.24

If this same buyer purchases in a Mello-Roos district carrying an additional 0.5% special tax, their effective annual property-related cost would rise by roughly $1,900 per year, or about $158/month, on top of the figures shown here, a cost this calculator's statewide baseline does not include since Mello-Roos taxes are set district by district rather than statewide.

• Mello-Roos special tax districts. Many newer California subdivisions carry a Community Facilities District special tax that is not capped by Proposition 13 and is not reflected in this calculator's 0.73% baseline.
• Prop 13's 2% annual assessment cap over time. This calculator models a snapshot at purchase; it does not project how a buyer's future tax bill will grow more slowly than home value appreciation in the years after purchase, which is one of Prop 13's central long-term effects.
• Reassessment triggers. Certain transfers, new construction, and some parent-child transfers can trigger reassessment outside a normal resale, changing the assessed value base the 1% rate applies to.
• Private mortgage insurance (PMI). Below 20% down, most conventional loans require PMI, which is not added separately even when the low-down-payment scenario toggle is used.
• Closing costs, county documentary transfer tax, and prepaid escrow reserves, which affect cash needed at closing but not the ongoing monthly payment modeled here.

• Assuming next year's tax bill will match this year's estimate exactly. Under Prop 13, the assessed value used for tax purposes typically rises a capped 2% per year after purchase, so this calculator's estimate is most accurate for the first year of ownership.
• Overlooking Mello-Roos or other special assessments when comparing two similarly priced homes in different California subdivisions, since one may carry a meaningfully higher all-in property tax burden than the other.
• Skipping PMI in a low-down-payment scenario, which understates the true monthly obligation for any purchase financed above 80% loan-to-value.
• Confusing assessed value with market value in later years of ownership, since a long-held California property's assessed value is often well below its current market value thanks to the 2% annual cap.
• Not shopping insurance regionally, since California homeowners insurance premiums, especially in wildfire-exposed areas, have risen sharply and can push real costs well above the flat $125/month placeholder used here.

• California State Board of Equalization: Proposition 13 assessed value and tax rate guidance
• California county assessor offices: parcel-level assessed value, millage, and Mello-Roos district lookups
• Consumer Financial Protection Bureau (CFPB): mortgage disclosure and PMI requirements under Regulation Z
• California Department of Insurance: homeowners insurance market data