ADU Cost & ROI Calculator
What a Long Beach ADU runs, all-in, as a RANGE from cited sources — and what the rent does to it. Planning math for the first conversation, printed with its homework showing.
A planning range, not a bid, a quote, or a permit prediction. Cost presets were re-verified on November 1, 2026 against the published sources listed below and go stale — review quarterly. Rent, fees, and utility work are your project's numbers; confirm current Long Beach rules and fees with the city before you rely on any figure here.
PLANNING RANGE — NOT A BID, QUOTE, OR APPRAISAL. Cost ranges below come from the published sources cited on this page, checked November 1, 2026. Your parcel (utilities, slope, trees, fire sprinklers, coastal or historic overlays), your design, and 2026 labor decide the real number. Rent is an input you supply — this page does not estimate rent for any address. Presets checked November 1, 2026 — review quarterly.
How the math works
Hard cost = size × the per-sq-ft range for your ADU type. Soft costs (design, engineering, permits-side work) are estimated at 12–15% of hard cost. Contingency applies to hard + soft + fees + site allowance. The all-in range = hard + soft + fees + site/utility allowance, plus contingency. Returns are computed at the RANGE MIDPOINT: NOI = rent × 12 × (1 − vacancy) × (1 − expense ratio); yield on cost = NOI ÷ all-in cost; simple payback = all-in ÷ NOI; with financing, annual debt service = financed amount × 12 × the mortgage factor at your rate and term, and cash-on-cash = (NOI − debt service) ÷ cash in.
The presets, with sources: (1) ADU Pilot’s California cost calculator (adupilot.com, 2026; its cited sources include the UC Berkeley Terner Center, Snap ADU 2026, and Angi) lists Los Angeles hard costs at: detached $300–$450/sq ft, attached $250–$400, garage conversion $150–$300, JADU $150–$275, with soft costs at 12–15% of construction. (2) ADU West Coast’s Long Beach cost study (“Multifamily ADU Cost Breakdown: 4 Detached Units in Long Beach (2026),” aduwestcoast.com) puts a one-off detached 750 sq ft ADU on a single-family Long Beach lot at roughly $285,000–$310,000 all-in, with a detached cost build-up around $300/sq ft at the middle tier and utility-upgrade surprises of $15,000–$40,000 — which is why the site/utility allowance line defaults to zero but exists, labelled, for you to raise. (3) Impact fees: California law (Gov. Code §66324, as amended by SB 543) bars impact fees on ADUs under 750 sq ft (and JADUs up to 500 sq ft); larger ADUs can be charged proportionally — the fees line is yours to set with the city’s current schedule. (4) Terner Center survey medians reported statewide (detached ≈ $300/sq ft total) corroborate the detached band. No preset here is a contractor’s bid, including ours.
A worked example
The defaults — detached, 750 sq ft, at the $300–$450 hard-cost band: hard cost $225,000–$337,500; soft costs $27,000–$50,625; 10% contingency on the stack puts the all-in range at $277,200–$426,938, midpoint $352,069. The ADU West Coast Long Beach datapoint for this exact home (750 sq ft detached, one-off) sits at $285,000–$310,000 — inside our band, toward its lower-middle, because a published local case prices easier than a range built to also cover hard sites. At $2,400 a month rent, 5% vacancy, 30% expenses, NOI is $19,152 a year: a 5.44% yield on cost at the midpoint (6.91% at the low end, 4.49% at the high end) and an 18.4-year simple payback. That is the honest Long Beach ADU story: a long-hold, equity-and-housing play whose return leans on appreciation and utility, not a quick cash-flow machine — and any calculator that shows you otherwise is selling something.
Questions from the field
How much does an ADU cost in Long Beach? Plan on an all-in range, not a point: a 750 sq ft detached unit models at $277,000–$427,000 on the cited 2026 sources, with a published Long Beach case study for exactly that unit at $285,000–$310,000. Garage conversions run far less ($150–$300/sq ft hard cost).
Are there impact fees on a Long Beach ADU? California law bars impact fees for ADUs under 750 sq ft; at or above that size, fees may be charged in proportion to the primary home. Other charges (school, utility connection) can still apply — the fees line in the tool is set from the city’s current schedule for your parcel.
What rent should I assume? Yours to enter — this page never estimates rent by address. ADU West Coast’s Long Beach study cites $2,400–$2,900 a month for a 750 sq ft 1-bedroom; use your street’s real leases, not a citywide average, and stress it at 5% vacancy.
Does an ADU pay for itself? On cash flow alone, at current Long Beach costs: slowly — the worked example pays back in about 18 years before appreciation, tax effects, and family-housing value. Owners who do it for a parent, an adult kid, or a 15-year hold are usually the satisfied ones.
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