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HCD March 2026Gov. Code §66311.5State-law screen

California ADU
Impact-Fee Screen

Check the statewide impact-fee exemption threshold or calculate the proportional factor for a larger ADU. This does not estimate the total permit bill.

Who it is for: California architects, contractors, and homeowners doing an early pre-design fee screen before obtaining current schedules from the city, county, school district, utility, and other serving agencies.

1
Classify the unit
Choose ADU or JADU and use interior livable space.
2
Enter both areas
The proportional factor compares the unit with the primary dwelling.
3
Verify local charges
Planning, building, school, utility, and other charges require current agency schedules.
Bounded result
The result addresses the impact-fee threshold and proportionality described in the March 2026 HCD Handbook. It does not determine an invoice, a school fee, a utility charge, or whether a named local charge is legally classified as an impact fee.
Impact-fee state-law screen
California model · HCD Handbook updated March 2026

How to use this calculator

1
Choose ADU or JADU
The March 2026 HCD Handbook states different impact-fee exemption thresholds: 750 square feet for an ADU and 500 square feet for a JADU.
2
Use interior livable space
Enter the area basis used by current State ADU Law, not gross building area or lot area.
3
Enter the primary dwelling area
For a nonexempt unit, proportionality is based on unit area relative to primary-dwelling area.
4
Verify every charge locally
Use the result only to review current written schedules with the permitting agency, school district, utility, and other serving agencies.

The formula

For the limited impact-fee screen implemented here:

ADU at or below 750 sq ft: impact-fee screen = exempt.
ADU above 750 sq ft: proportional factor = ADU interior livable area ÷ primary-dwelling area.
JADU: the current definition limits interior livable space to 500 sq ft; the HCD Handbook describes a 500-sq-ft impact-fee threshold.

If a verified comparable primary-dwelling impact-fee amount is entered, the worksheet multiplies it by the proportional factor. It does not add permit, plan-review, school, utility, connection, capacity, tax, or special-assessment charges.

Worked example

Example
A 1,000-sq-ft ADU with a 2,000-sq-ft primary dwelling is above the 750-sq-ft impact-fee exemption threshold. Its proportional factor is 0.50 (50%). If the user enters a verified $20,000 comparable primary-dwelling impact fee, the arithmetic comparison is $10,000. The serving agency must still identify the applicable charge and amount.

When this estimate will be off

  • This is a statewide impact-fee screen, not a fee quote, legal opinion, permit-cost estimate, or determination that a particular charge is an impact fee.
  • Planning, building, plan-review, school, utility, connection, capacity, tax, special-assessment, and other charges are not totaled.
  • School districts are authorized, but not required, to levy qualifying fees for ADUs larger than 500 square feet; obtain the current district decision and rate.
  • Utility treatment depends on the construction facts and current law. This route intentionally does not issue a utility-fee verdict.
  • Local waivers and less restrictive rules may reduce charges. Confirm the law and agency schedules effective on the application date.

Frequently asked questions

A common mistake: This is a statewide impact-fee screen, not a fee quote, legal opinion, permit-cost estimate, or determination that a particular charge is an impact fee.

No. State law does not supply one statewide permit price. The result screens the impact-fee exemption threshold and proportional factor only. Obtain current written schedules from each relevant agency.

For an ADU above the exemption threshold, the March 2026 HCD Handbook describes proportionality in relation to ADU area divided by primary-dwelling area.

No. It is arithmetic applied to a user-entered comparison amount. It does not identify the legally applicable fee base, classify a charge, or replace an agency calculation.

No. The page flags their separate review but does not calculate them because current district schedules, utility rules, and project facts are required.

Sources

Sources and review record

Sources and method basis

Limitations

  • Screens state impact-fee exemption and proportionality only; payable permit, planning, school, utility, connection, capacity, tax, special-assessment, and other charges require current agency schedules and project facts.

This free California ADU Fee Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.