A pattern day trader is generally defined in FINRA Rule 4210 as any customer who executes four or more round-trip day trades within any five successive business days. FINRA Rule 4210 is substantially similar to New York Stock Exchange Rule 431. If, however, the number of day trades is less than or equal to 6% of the total number of trades that trader has made for that five business day period, the trader will not be considered a pattern day trader and will not be required to meet the criteria for a pattern day trader.
A non-pattern day trader (i.e. someone with only occasional day trades), can become designated a pattern day trader anytime if he meets the above criteria. If the brokerage firm knows, or reasonably believes a client who seeks to open or resume trading in an account will engage in pattern day trading, then the customer may immediately be deemed to be a pattern day trader without waiting five business days.