What it is
At-will employment means no law requires two weeks of notice. It is a professional custom, and in some roles the employment contract, the handbook, or a client agreement makes it a contractual term. Giving notice protects the reference and keeps the payout window under the rules in force on your last day.
What to do about it: Notice in writing, dated, with your last day named. In a state that pays final wages on immediate quit-with-notice, the written notice is the fact that sets the clock.
Plain-language description of US practice, not legal, tax, or financial advice. The paired guide carries the citations, dates, and thresholds; the state pages carry the local windows.