If you use a trade name to do business with ( for example, your name is john doe and your business name is Painting Company) you will need to file a dba.
Businesses using a name other than the owner's legal name are required to register a DBA / Assumed Business Name Certificate. Note that you can incorporate or form an LLC instead of filing a DBA. If you are an LLC or Corporation you don't need a dba.
Users of a assumed business name other than their last name or the corporation's or LLC's legal name.
Filing takes an average of 3-5 Business Days - could take longer in some states.