An impact fee must be supported by a study that connects new development to a capital need and to the amount charged.
Level of service standard. The existing standard the community provides, measured — acres of park per thousand residents, gallons per day of capacity, response time. New development is charged to maintain that standard, not to improve it.
Demand units. How the need is generated — residents per dwelling unit, trips per thousand square feet, equivalent residential units — using local data where available and published sources otherwise.
Capital cost. The cost of facilities needed to serve new development at the existing standard, with a capital improvements plan identifying the projects.
Credits. For other revenues that will fund the same facilities — property taxes, grants, developer-constructed improvements — to avoid double charging.
Fee schedule by land use category, derived from the analysis rather than adopted at a round number.
Accounts and spending. Fees held in separate accounts by category, spent within a statutory period on facilities benefiting the payers, with refunds if not.
Updates. Periodically, since costs and standards change and a stale study is the usual basis for challenge.
Individual assessment. An option for an applicant to demonstrate a lower impact, which strengthens the scheme against constitutional attack.