Methodology

How we turn fee schedules into numbers

Every fee here comes from a document the city, county or state publishes. We never estimate a rate. When a fee depends on details we don’t have, we show the formula and leave it out of the modeled total.

Sources and checks

For each place we save a copy of each official fee schedule, ADU page or ordinance (HTML or PDF text) with the date we fetched it. Every rate in our data carries the exact line we read it from, and an automated check confirms that each quoted line still appears in the saved copy and that each number we use appears in its quote. Pages list every source with its effective date and the date we last checked it.

The four sizes

We model detached ADUs of 499 sq ft (just under the school-fee threshold), 750 sq ft (the largest with no impact fees), 1,000 sq ft and 1,200 sq ft (the most a city can cap a detached ADU at). The main home is assumed to be 2,000 sq ft, the example in the state’s ADU handbook. In the calculator you can enter your own size, main home and valuation.

State rules we apply

• Impact fees are $0 at 750 sq ft or less.
• Above 750 sq ft, per-home impact fees are multiplied by ADU sq ft ÷ main-home sq ft. Per-sq-ft impact fees already scale. When a city publishes a specific ADU amount, we use it as published.
• School fees are $0 under 500 sq ft. Where we haven’t confirmed the district’s own rate, we show the statewide Level 1 cap ($5.38/sq ft) as an upper bound, counted in the high total only.
• Utility connection charges are $0 for conversions of existing space.
• 2027 mode (SB 1117): impact fees count only the area over 750 sq ft. Where a city’s fee is a fixed per-ADU amount, we scale it by (sq ft − 750) ÷ sq ft and label the result as our estimate.

Low and high totals

The low total counts fees that apply to a typical project. The high total adds fees that may apply (location-dependent fees, optional reviews, school fees at the statewide cap, ranges a city publishes). When a city publishes a “typical” range rather than a rate (Mountain View’s and Palo Alto’s building permit estimates), we use its range and label it as the city’s estimate.

What we leave out

Fees based on construction valuation are left out of modeled totals unless the city publishes a valuation per sq ft; the calculator includes them once you enter a valuation. Water and sewer connection charges from separate districts, encroachment permits, tree removal, fire sprinklers, special assessments and utility-company work are usually not included; each page lists its gaps. Totals are not a quote. Confirm with the jurisdiction.

Permits issued

ADU building permits per year come from the Housing Element Annual Progress Reports jurisdictions file with HCD (Table A2), published on data.ca.gov. Counts are as reported and may include junior ADUs.

Places we couldn’t model

• Cupertino: We couldn't find the adopted FY 2026-27 fee schedule online. The only schedules we could read were draft resolution attachments from 2024 and 2025 ("Resolution 25-XXX", fees effective July 6, 2025), which may be out of date.

Places in the queue

Requested places we haven’t added yet, and why:

• Santa Clara: The FY 2026/27 Municipal Fee Schedule (adopted April 21, 2026) wasn’t yet captured in full; we only have the minor-permits sheet.
• Salinas: Research started; fee schedule not yet captured and modeled.
• Monterey: Not yet researched.
• Monterey County (unincorporated): Not yet researched.
• Los Angeles: Research started; fee schedule not yet captured and modeled.
• San Diego: Research started; fee schedule not yet captured and modeled.
• Sacramento: Research started; fee schedule not yet captured and modeled.

Corrections

If a fee changes or we misread a schedule, the page will be corrected and dated, and the change logged on the news page. Each page links straight to its official sources so you can check us.