Calculators / Measuring and costs

ADU cost calculator

Put in the size and kind of ADU. You’ll get the cost to build it and, in the City of San Diego, every permit fee from the city’s own schedule.

Updated November 2026 · How we check our numbers

Expect to pay about

$222,247

$200,000 to build 800 sq ft, plus $22,247 in City of San Diego permit fees, before water and sewer capacity fees.

Building it: $200,000
City fees: $22,247
A sq ft, all in: $278

Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

Pick a planSan Diego County’s free ADU plans, 600 to 1,200 sq ft, and the lot space each needs.

build = 800 sq ft × $250 = $200,000

plan check $8,085 + inspections $8,402 + $737 + $529.71 + $12.16 + water/sewer review = $17,943

school fees = 800 × $5.38 = $4,304

What goes into it

Detached, new build

Building it: $200,000800 sq ft × $250 a sq ft, the 2021 California median (Terner Center)
$200,000
Plan check (IB 501, single-dwelling row)
$8,085
Inspections (IB 501)
$8,402
General Plan Maintenance Fee
$737
Addressing, if it gets its own address
$530
Mapping fee
$12
Water and sewer plan check, same meter
$177
School fees, 800 sq ft × $5.38 (San Diego Unified)
$4,304
Development impact fees: none for the first two ADUs on a lot
$0
Water and sewer capacity feesSet during plan review, by the plumbing fixtures it adds
at review

Fees as published; the city confirms them when it reviews your plans.

Impact fees

San Diego waives development impact fees on the first two ADUs on a lot at any size, unless they’re built under the ADU bonus program; then fees apply above 750 sq ft (Municipal Code § 142.0640).

School district

San Diego Unified charges $5.38 a sq ft. Parts of the city are in other school districts, which set their own rate; the city tells the district your new space.

Building cost

Terner Center’s 2021 survey of California ADU owners put the median at $150,000, or $250 a sq ft, and 37% under $100,000. It’s the best published figure we found; costs have risen since, so put in a quote when you have one.

How we work it out

Building cost is the size times a price per square foot: your quote if you have one, or $250, the median a 2021 UC Berkeley Terner Center survey of California ADU owners found ($150,000 for the median ADU, and 37% under $100,000). It's the best published figure we found, but it's from 2021 and covers every kind of ADU, so a quote beats it.

For the City of San Diego the fees come from Information Bulletin 501 (August 2026). An attached ADU or junior ADU up to 1,100 sq ft, or a detached one up to 500 sq ft, pays $3,512.92 plan check and $2,228.29 inspection for the first 500 sq ft, plus $6.98 and $4.46 a sq ft over. A bigger detached ADU pays $8,085.26 and $8,401.90. On top: the $737 General Plan Maintenance Fee, $529.71 for an address, $12.16 mapping and the water and sewer plan check ($176.57, or $353.13 with a new meter).

The city waives development impact fees on the first two ADUs on a lot at any size (Municipal Code § 142.0640). School fees apply from 500 sq ft of new space; San Diego Unified charges $5.38 a sq ft, the state's Level I rate. Water and sewer capacity fees are set during plan review, from the fixtures you add, so they're listed but not priced. Elsewhere in California, state law bars impact fees on an ADU of 750 sq ft or less.

Where the numbers come from

ADUs

More calculators

All calculators

Your ADU