Published: 26 Oct 2026 · Last verified: 26 Oct 2026 · Next review: Jan 2027 Cost figures are re-checked against permit records quarterly. Changes are logged in Corrections.
Impact fees are the ADU line most likely to surprise you — in both directions. One homeowner pays nothing. Another, in a different city, pays five figures for the same size unit. Both are following the same state law. The difference is what their city charges, and whether their ADU crosses a single threshold: 750 square feet.
This post explains what impact fees are, what they are not, how the 750 rule works, what changes on January 1, 2027, and what real California cities actually charge.
What an impact fee is — and is not
An impact fee is a one-time charge on new development to pay for the public facilities that development will use: parks, roads, fire stations, police facilities, storm drainage, libraries, and similar capacity. The legal framework is California’s Mitigation Fee Act, and the ADU-specific rules sit in Government Code section 66311.5.
Three things impact fees are not:
- Not permit processing fees. Plan check, inspection, and issuance charges pay for the city’s cost of reviewing your project. They apply at any ADU size and are a separate line — see ADU soft costs.
- Not school fees. School district developer fees are levied by school districts under Education Code section 17620, with their own 500 sq ft threshold and their own rates (up to the 2026 Level 1 maximum of $5.38 per sq ft). See ADU school fees, explained.
- Not connection or capacity charges. Water and sewer connection fees, meter charges, and utility capacity charges are separate regimes with their own rules — and SB 1117 expressly leaves them out of its 2027 change.
If a quote lumps all four together as “city fees,” ask for the split. Only the impact-fee line follows the 750 rule below.
The 750 rule
Section 66311.5 sets two cases:
- ADU of 750 sq ft or less: no impact fees. Not reduced, not deferred. Zero. Cities, counties, and special districts may not impose them.
- ADU above 750 sq ft: fees must be proportionate to the primary dwelling. The standard formula is:
(ADU sq ft ÷ house sq ft) × the single-family dwelling fee
So an 800 sq ft ADU behind a 1,600 sq ft house pays about half the dwelling fee. An 800 sq ft ADU behind a 3,200 sq ft house pays about a quarter. The house size matters as much as the ADU size — which is why this site’s fee calculator asks for both.
Since a 2025 cleanup bill (SB 543), the 750 is measured in interior livable space. And some cities waive ADU impact fees entirely, at any size, by local ordinance.
What real cities charge at 800 sq ft
The law sets the threshold. Each city sets the price of crossing it. These figures are from this site’s 750 sq ft cliff explainer, which cites each city’s published fee schedule:
| City | At 749 sq ft | At 800 sq ft | How the fee works |
|---|---|---|---|
| Torrance | $0 | $2,243.47 flat | A single schedule line: “ADU 750 SF or greater” |
| Sacramento | $0 | ~$5,728 city impact fees | The city’s own free plans are drawn at 747 sq ft for a reason |
| Glendale | $0 | up to $4,700 | The “50 sq ft cliff” — 749 pays nothing, 800 pays the schedule maximum |
| Fullerton | $0 | ~$6,411 pro-rata | Development impact fee on the full 800, scaled to the house |
| Palo Alto | $0 | ~$8,000–$20,000 | The steepest per-foot cliff: parks fee near $18.65 per sq ft before proportionality |
| Anaheim | $0 | ~$10,411 | The heaviest published development-fee load in the series |
| Salinas | $0 | $0 | No cliff at all — the city waives ADU impact fees at every size |
| Oakland | $0 | $0 | Impact fees exempt for ADUs by ordinance |
Two things stand out. First, the range: the same 51 square feet costs $2,243 in Torrance and up to $20,000 in Palo Alto. Second, the cities with no cliff at all — a local policy choice their fee schedules state in plain language.
One more example, with proration made explicit: Ontario’s published schedules are area-specific and prorated rather than summed. For an 800 sq ft ADU behind a 1,600 sq ft house, the live calculator range is $20,134–$30,624 including school fees ($18,798–$29,288 impact fees plus $1,336 school fees, by area). Run your own house size through the fee calculator — the range moves with it.
What changes on January 1, 2027: SB 1117
SB 1117 (Chapter 809, signed September 29, 2026) narrows the charge for a homeowner’s first two ADUs. From 2027:
- Impact fees apply only to the area in excess of 750 square feet. An 800 sq ft ADU is charged on 50 sq ft, not 800. Under the old proration, that ADU behind a 1,600 sq ft house paid on half the dwelling fee; under SB 1117 it pays on 50 sq ft worth.
- A third or further ADU keeps the current rule — full proration on the whole ADU area.
- Connection and capacity charges are excluded from the change.
- Charter cities are included — the rule applies statewide.
The calculator on this site already shows the 2026-versus-2027 comparison. For the full savings list and the cities where waiting actually pays, see the SB 1117 post.
A practical consequence: the 749 sq ft design trick that dominates today — Sacramento’s free plans drawn at 747, Salinas’s 749 and 746 options, Fontana’s 738 — matters less after 2027 for a first or second ADU, because the fee above 750 shrinks to the excess area only. It still matters for a third ADU, and for school fees, which SB 1117 does not touch.
How to look up your city
- Run your address through the fee calculator — it covers 156 California jurisdictions with 409 verified line items, and it asks for the house size because proration requires it.
- Compare verified city schedules directly: Glendale, Torrance, Sacramento, Anaheim, Oakland.
- If your city’s schedule lists a flat ADU line, check whether it says “750 SF or greater” — older schedule wording sometimes predates the current exemption, and state law controls.
If your city’s schedule is not in the database yet, or a line looks wrong, tell us through Corrections. Every figure on this site is checked against the published schedule, not a quote or a forum post.
Put your own quote in these six rows
We made a blank version of the six-phase ledger. Drop your contractor’s numbers into it and see which line doesn’t match ours.
Download the worksheet — CSV (import to Google Sheets), no email required
Want the regional benchmark ranges for each phase, updated quarterly?
Methodology and sources
City figures in the table are drawn from this site’s 750 sq ft cliff explainer, which cites each city’s published fee schedule. The Ontario range is from this site’s live fee calculator, reflecting the corrected proration (area schedules applied separately, not summed). Statutory rules are from the cited code sections.
| Input | Source |
|---|---|
| ADU impact fee rule: 750 exemption, proration | Gov. Code §66311.5 |
| SB 1117: excess-area-only charge from Jan 1, 2027 | SB 1117 post |
| City cliff figures (Torrance, Sacramento, Glendale, Fullerton, Palo Alto, Anaheim, Salinas, Oakland) | The 750 sq ft cliff, explained |
| Ontario prorated range, 800 sq ft ADU / 1,600 sq ft house | Fee calculator |
| School fees as a separate regime, 500 sq ft threshold | ADU school fees, explained |
| Statewide ADU rules | California HCD ADU Handbook |
Check this number against your own address
Most California jurisdictions publish permit records online, including the declared construction valuation for each project. That declared valuation is the closest thing to a real local baseline you can get without paying anyone.
- Open EPIC-LA for unincorporated LA County, or the LADBS Permit & Inspection Report for addresses inside the City of Los Angeles.
- Search recent ADU permits within about a mile of your address.
- Compare the declared valuation to the phase totals on this page.
Declared valuations run below contract price — treat them as a floor, not a total. Full detail on Methodology.
If your local numbers diverge meaningfully from ours, we want to know. See Corrections.
Our position
We don’t build ADUs. We don’t sell plans. We don’t sell your information to contractors. No figure on this site has been paid for or reviewed by anyone whose costs we publish. More on About.
Figures are California, 2026, from published city fee schedules and this site’s verified fee database. Costs vary by jurisdiction and house size. This is construction cost information — not a quote, and not legal, engineering, or financial advice. Confirm requirements with your local building department and a licensed California contractor.
Frequently asked questions
What is an ADU impact fee?
A one-time charge a city, county, or special district levies on new development to pay for the public facilities that development will use — parks, roads, fire, police, drainage, and similar capacity. For ADUs, California law caps when and how these fees apply: none at 750 sq ft or less, and only a prorated share above it.
Why does my neighbor’s ADU owe $0 in impact fees?
Because it is 750 sq ft or less. State law (Gov. Code section 66311.5) bars impact fees on ADUs at or under that size. Some cities go further and waive ADU impact fees at any size — Salinas and Oakland among them.
How is the impact fee calculated above 750 sq ft?
By proportion to the primary dwelling: roughly (ADU square feet divided by house square feet) times the single-family fee. An 800 sq ft ADU behind a 1,600 sq ft house pays about half the dwelling fee. From January 1, 2027, SB 1117 narrows that further for a homeowner’s first two ADUs, charging only the area above 750.
What changes on January 1, 2027?
SB 1117 (Chapter 809) provides that for no more than two ADUs on a lot, impact fees apply only to the area in excess of 750 square feet. An 800 sq ft ADU would be charged on 50 sq ft, not 800. A third or further ADU keeps the current full proration, and connection and capacity charges are excluded from the change.
Do impact fees include school fees?
No. School district developer fees are a separate regime under Education Code section 17620, levied by school districts rather than cities, with their own 500 sq ft threshold and their own rates. An ADU between 500 and 749 sq ft pays school fees but no city impact fees.