The instructions to Forms 1040EZ, 1040A, and 1040 include three charts for determining who must file and who should file a tax return.
Chart A - For Most People Who Must File is for individuals who cannot be claimed as a dependent on another taxpayer's return.
Chart B - For Children and Other Dependents applies to individuals who can be claimed as dependents on another taxpayer's return.
Chart C - Other Situations When You Must File should be reviewed for all individuals as a last step after using the other charts.
Even individuals who are not required to file should file a return to claim a refund of withheld taxes, the earned income tax credit, the additional child tax credit, or if they qualify for the health coverage tax credit or other credits.