Free California planning tool

California ADU ROI Calculator

Test an income-producing ADU using your own project cost, rent, expenses and financing — with transparent formulas, break-even rent and a stress test instead of hidden market multipliers.

No login requiredSaved only in this browserRental-income scenario, not financial advice

Run the rental economics from numbers you can defend.

Start with the all-in ADU project cost. If you used our budget calculator on this device, import that saved total instead of rebuilding it here.

1 · Project + rent

What will you invest, and what rent are you testing?

Sample assumptionInclude design, permits, construction, utilities, site work, carrying costs and contingency.
No saved budget found.
Build all-in cost with California guardrails

Start with a base project cost that excludes the fee/solar/site allowances below. The tool applies current California thresholds where the law is clear and leaves local dollar amounts visible.

A city preset supplies official source links and local verification prompts. It does not silently inject dollar amounts.
Used only for the current proportional impact-fee estimate at/above the state threshold.
Enter the local impact-fee amount that would apply to a comparable new primary dwelling, if known.
District-specific. Leave at zero until verified.
Applied only to a newly constructed detached ADU.
Use a utility or contractor allowance; no statewide fixed amount is assumed.
SB 1117 watch: as of September 5, 2026, the bill is on the Governor’s desk. Its excess-over-750 formula is not used here unless it becomes law.
Guardrail-built all-in cost$0
Sample assumptionReplace with a defensible rent from comparable long-term rentals.

2 · Operating assumptions

Model what sits between gross rent and cash flow.

Vacancy allowance
5%
Maintenance reserve
5%
Property management
0%
Zero is treated as unresolved.

3 · Financing

Model the stabilized rental period.

This is not a construction-draw calculator. Use the debt you expect to carry after completion.

Browser-only save: this scenario is stored in the same local project record as your checklist and budget. Nothing is sent to ADU Project Planner.

Stress test

What if rent or project cost moves by 10%?

Each cell shows first-year cash-on-cash return. The matrix changes only the inputs you supplied; it is not a market forecast.

Rent ↓ / Cost →Cost -10%Your costCost +10%

Transparent formulas, not an appraisal.

The calculator separates rental operations from financing so you can see exactly which layer is helping or hurting the project.

Net operating income

Gross rent minus vacancy, maintenance/management reserves and fixed annual operating expenses.

Cash-on-cash return

Annual cash flow after debt service divided by cash invested.

Break-even rent

Monthly rent required for modeled income to cover operating expenses and debt service.

No automatic appreciation claim: an ADU can add property value, but the amount is property- and market-specific. This calculator does not manufacture an appraised-equity gain.
California property-tax planning: completed new construction can create a new assessed value for the newly constructed portion. Enter an assessor-based annual tax estimate rather than assuming zero.
Build the project budget →View My ADU Project →
Planning use only. This calculator is not financial, tax, lending, appraisal or investment advice. The optional California Cost Guardrails apply state-law thresholds where the rule is clear, but they do not invent local fee schedules, solar quotes, utility costs or construction prices. Verify current requirements with the California HCD ADU resources, California Energy Commission ADU FAQs and Board of Equalization new-construction guidance.