If you're reading this material, you probably don't have any doubt about whether you need to file a tax return.
Filing thresholds — the basic rule is that, if you are a citizen or resident of the United States, or a resident of Puerto Rico, you must file a tax return if you have gross income at or above a certain dollar amount. The dollar amount depends on your filing status and whether you are 65 or older at the end of the year. The same rules apply to U.S. citizens living outside the United States.
Rules for dependents — you may have questions about whether your child, parent, or some other person for whom you're responsible needs to file a return.
Others who must file — even if the other rules don't apply, certain people must file an annual return.
Most small business owners need to file, because anyone with net self-employment income of $400 or more must file a tax return to report and pay their self-employment tax.
If you are a nonresident alien, different rules may apply which are not covered here. See IRS Publication 519, U.S. Tax Guide for Aliens.