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California ADU Cost & ROI Calculator

What an ADU or garage conversion costs to build in 20 California cities, with each city's permit, impact and school fees and the state exemptions applied, and how long the rent takes to pay it back.

Updated · By Niraj Kumar · 11 sources

1. The ADU

Type of ADUType of ADU
sq ft
1501,200

School fees start above 500 sq ft and impact fees at 750 sq ft.

Finish levelFinish level
sq ft

Impact fees from 750 sq ft are scaled by the ADU's size against the house.

2. Site work

ft

Distance from the house's sewer lateral to the ADU.

ft
ft
Main electrical panel upgradeMain electrical panel upgrade
%
0%25%

Architect, structural engineer, Title 24 and survey, as a share of the build. About 4% with a city pre-approved plan.

%
0%30%

3. Los Angeles fees

$

Los Angeles estimate.

$

Waived: under 750 sq ft (state law).

$

Charged on new detached and attached units.

$

$5.38 a sq ft on the whole unit.

4. Rent and financing

Rented asRented as
$

HUD's FY 2026 fair market rent for the metro, a conservative figure. Enter a local listing to replace it.

%
0%50%
%

Charged on the ADU's construction cost only; the house is not reassessed.

$
% of rent
0%30%
How you payHow you pay
years
5 yrs30 yrs
%

Net rent ÷ cap rate is how appraisers value income. 4-6% is typical for California rentals.

Total cost, Los Angeles$314,980$525 a sq ft, $16,728 of it fees

At 500 sq ft it would pay no school fees, saving $3,228.

Construction
$298,252
build, site work, design and contingency
City and school fees
$16,728
Monthly cash flow, year one
$1,466
on $2,085 rent
Payback
14.4 years
5.6% cash-on-cash in year one
Value added
$351,732
$36,752 more than it costs, at a 5% cap rate
Where the money goes600 sq ft detached ADU, standard finish
  1. 1Construction$241,500
  2. 2Contingency$25,358
  3. 3Design and engineering$19,320
  4. 4Utility trenching$12,075
  5. 5Permit and plan check$9,000
  6. 6Sewer and water capacity$4,500
  7. 7School fees$3,228
Cumulative cash flow from rentStill to recoverAhead
$-400 K$-300 K$-200 K$-100 K$0$100 K$200 KPayback, year 14.4048121620
Year-by-year rent and cash flowShow
YearRent collectedRunning costsLoanCash flowCumulative
1$23,769$6,182$0$17,587-$297,394
2$24,482$6,335$0$18,147-$279,247
3$25,217$6,492$0$18,725-$260,522
4$25,973$6,652$0$19,321-$241,201
5$26,752$6,817$0$19,935-$221,266
6$27,555$6,986$0$20,569-$200,697
7$28,381$7,159$0$21,222-$179,475
8$29,233$7,337$0$21,896-$157,579
9$30,110$7,520$0$22,590-$134,989
10$31,013$7,707$0$23,306-$111,683
11$31,944$7,899$0$24,045-$87,638
12$32,902$8,096$0$24,806-$62,832
13$33,889$8,298$0$25,591-$37,241
14$34,906$8,505$0$26,400-$10,840
15$35,953$8,718$0$27,235$16,395
16$37,031$8,936$0$28,095$44,490
17$38,142$9,160$0$28,982$73,472
18$39,287$9,390$0$29,897$103,369
19$40,465$9,626$0$30,840$134,208
20$41,679$9,867$0$31,812$166,020

How the California ADU Cost & ROI Calculator works

A new detached ADU in California typically costs $200,000 to $350,000 all in, or $300 to $500 a square foot; a garage conversion costs 35-45% less. City and school fees add $3,000 to $20,000. Staying under 750 sq ft avoids impact fees, and at 500 sq ft or less school fees too.

The build cost is the floor area times a cost per square foot for the type of ADU and the level of finish, adjusted for local building costs, plus trenching for sewer, water and power, design and a contingency. Fees follow state law: no impact fees under 750 sq ft and only a proportional share above, no sewer or water capacity charge on a conversion, and no school fee at 500 sq ft or less. The return compares rent, after vacancy, property tax on the added value, insurance, upkeep and any loan, with the cash you put in.

Cost = sq ft × rate₍type, finish₎ × city index + utility runs + panel + design + contingency + fees fees = permit + impact × (ADU ÷ house, from 750 sq ft) + capacity (new builds) + school × sq ft (over 500) Payback: Σ₍y₎ (rent × (1 − vacancy) − tax − insurance − upkeep − loan) ≥ cash invested
city index
Local construction cost against the California average
impact
City parks, traffic and facilities fees, charged only from 750 sq ft
capacity
Sewer and water capacity charges, waived for conversions
school
District developer fee, at most $5.38 per sq ft in 2026
NOI
Net operating income: rent after vacancy and running costs, before the loan
City and school fees for a new detached ADU behind a 1,600 sq ft house, as of 2026-10-05
City600 sq ft800 sq ft1-bed rentFee figures
Los Angeles$16,728$21,304$2,085Estimate
San Diego$23,450$24,526$2,459City schedule
San José$9,519$21,407$2,982City schedule
San Francisco$14,228$19,304$2,325Estimate
Fresno$6,974$14,232$1,350City schedule
Sacramento$8,978$14,304$1,600City schedule
Long Beach$8,872$13,314$2,085City schedule
Oakland$11,728$20,804$2,325Estimate
Bakersfield$8,228$12,804$1,200Estimate
Anaheim$10,228$17,804$2,350Estimate
Santa Ana$9,728$16,304$2,350Estimate
Riverside$8,228$15,304$1,700City schedule
Irvine$10,728$19,804$2,350Estimate
Chula Vista$9,228$22,304$2,459Estimate
Fremont$10,228$14,304$2,325Estimate
Santa Clarita$13,728$21,304$2,085Estimate
San Bernardino$8,228$14,304$1,700Estimate
Pasadena$11,128$13,804$2,085City schedule
Berkeley$9,728$13,304$2,325Estimate
Santa Monica$14,728$23,804$2,085Estimate

Worked example

A 600 sq ft detached one-bedroom ADU at standard finish behind a 1,600 sq ft house in Los Angeles, with utility lines run 50 ft from the house, paid in cash.

  1. 1Construction: 600 sq ft at about $402 a sq ft is $241,500; utility trenching adds $12,075, design $19,320 and a 10% contingency $25,358
  2. 2Fees: $9,000 in permit and plan check, no impact fees (under 750 sq ft), $4,500 in sewer and water capacity, and $3,228 in school fees
  3. 3Rent of $2,085 a month less 5% vacancy, property tax, insurance and upkeep leaves $17,587 a year

The ADU costs about $314,980 all in, $525 a sq ft, of which $16,728 is fees. The rent repays it in about 14.4 years, a 5.6% cash return in the first year.

Frequently asked questions

How much does it cost to build an ADU in California?

Most new detached ADUs cost $300 to $500 a square foot all in, so a 600 sq ft unit runs roughly $200,000 to $300,000, more in San Francisco and the coastal cities and less in the Central Valley. Attached ADUs cost a little less, and garage conversions and junior ADUs, which reuse an existing structure, cost about half as much per square foot. Pick a city in the calculator for its local cost level and fees.

Does an ADU add value to my property?

Usually more than it costs where rents are high. Appraisers value rental property by its income: net rent divided by a capitalisation rate. At a 5% cap rate, an ADU netting $20,000 a year adds about $400,000 of value. Lenders and appraisers vary in how much credit they give a single-family home's ADU, so treat the figure as a ceiling.

Are ADUs under 750 square feet exempt from impact fees in California?

Yes. Government Code §66324 bars cities, counties and special districts from charging impact fees on an ADU under 750 sq ft. From 750 sq ft they may charge, but only in proportion to the ADU's size against the main house: a 750 sq ft ADU behind a 1,500 sq ft house pays at most half the fee a new house would. Building permit and plan check fees still apply at any size.

Do ADUs pay school fees?

Only over 500 sq ft. Education Code §17620 exempts ADUs of 500 sq ft or less. Above that, the school district charges its developer fee on every square foot, at most $5.38 a sq ft from January 2026. A 600 sq ft unit pays about $3,200; staying at 500 sq ft avoids it entirely.

Why is a garage conversion so much cheaper?

The shell, roof and slab already exist, so the build cost per square foot is roughly half that of a new detached unit, and state law bars sewer and water capacity charges on an ADU made inside existing space. Expect to add insulation, windows, a new floor over the slab and plumbing that may need a trench to the sewer line.

Will an ADU raise my property tax?

Only on the ADU. Under Prop 13 the assessor adds the value of the new construction to your existing assessed value, without reassessing the main house. At the base 1.1% rate, a $250,000 ADU adds roughly $2,750 a year, rising at most 2% a year after that.

Do I have to live on the property to rent out an ADU?

No, for an ADU: state law has barred owner-occupancy requirements on ADUs since 2020 and made that permanent from 2025. A junior ADU, which is carved out of the house, still requires the owner to live in either the house or the JADU. Cities may require rentals of 30 days or longer, and most do, which rules out short-term holiday lets.

Sources

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