State conformity explained

Even if a federal rule changes, states can treat it differently. This guide focuses on what “conformity” means in practice and how to verify it.

What “state conformity” generally means

Some states automatically follow certain parts of federal definitions; others decouple or adopt changes on a different timeline. This is why a federal estimate may or may not map cleanly to state withholding or filing rules.

What to check (without guessing rates)

• Whether your state references federal income definitions and how it updates those references.
• Whether your state provides specific guidance for wage withholding and residency/part‑year situations.

Tip: each state calculator page includes Official state tax pointers and Official sources links so you can check the state’s own guidance.

See also: State income tax conformity overview.