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Mello-Roos Calculator

Enter your home value, base tax rate, and special assessment to estimate your total tax.

How it is calculated

The estimate adds two parts. The base tax is assessed value × base rate ÷ 100, where the base rate is a percentage (1.1 means 1.1%). The Mello-Roos part is the annual special tax amount in dollars that you type in; it is added as given and is not scaled by the home value. Then total = base tax + special tax, monthly = total ÷ 12 and effective rate = total ÷ assessed value × 100. Amounts are shown in US dollars. If the assessed value is 0 the effective rate is shown as 0%. The tool does not look up any district: the base rate, the special tax figure and any yearly increase must come from your own tax bill or the district's documents.

Worked example

A home is assessed at $750,000, the base rate is 1.1% and the annual special tax is $3,200. Base tax: 750,000 × 1.1 ÷ 100 = $8,250.00. Add the special tax: 8,250 + 3,200 = $11,450.00 per year. Divided by 12, that is $954.17 per month. The effective rate is 11,450 ÷ 750,000 × 100, which the tool shows as $11,450.00 total annual cost and an effective rate of 1.53%.

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Common mistakes

  • Entering the base rate as a decimal fraction (0.011) instead of a percentage (1.1). The base tax would then be about one hundredth of the correct amount.
  • Typing the special tax as a percentage or as a monthly amount. The field is the yearly dollar amount, as printed on the annual tax bill.
  • Using the purchase price when the assessed value will differ. After a sale the assessed value may be reset, so check what value the county will actually use.
  • Assuming the special tax stays constant. Some districts include a yearly escalator, so a single year's figure understates the long-run cost.
  • Leaving out other line items on the bill, such as voter-approved bonds or other direct charges, which belong in either the base rate or the special amount if you want the true total.

Sources

About this calculator

Mello-Roos refers to a special tax levied on homes within a Community Facilities District (CFD) in California, created under the 1982 Mello-Roos Community Facilities Act to fund infrastructure — schools, roads, sewers, parks — in newly developed areas that wouldn't otherwise generate enough property tax revenue for those improvements. The total annual tax bill combines the standard base property tax (roughly the assessed value times the base rate) with the separate flat or formula-based Mello-Roos special assessment, and dividing the total by 12 gives the monthly cost.

Homebuyers and real estate agents use this calculator to estimate the true carrying cost of a property in a CFD, since Mello-Roos assessments can add a meaningful amount on top of the base property tax rate and typically don't show up clearly in a simple "tax rate" listing. Because these assessments can run for 20–40 years and sometimes decrease over time as bonds are paid off, buyers evaluating new developments in California often check whether a home carries a Mello-Roos district before comparing it to a similar home without one.

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  • Editorial team

    When comparing a Mello-Roos home with a similar one outside a district, look at the effective rate rather than the dollar total. With the default figures, 500,000 assessed, a 1.1 base rate and a 2,400 special tax, the district adds 0.48 percentage points and the effective rate lands at 1.58%. This tool covers California-style CFD taxes only. Does your bill show an annual escalator, and how much did it add last year?

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