How much someone has to earn before being required to file a federal tax return depends on age and filing status, according to the IRS. For most taxpayers with a single filing status under 65 at the end of 2014, gross income must be at least $10,150.
For individuals over 65 at the end of 2014 and with a single filing status, gross income must be at least $11,700 to be required to file, notes the IRS. For head of household filing status, gross income must be at least $13,050 if under 65 and $14,600 over 65. If married and filing jointly, the limits on gross income are higher than if single. There are special rules for dependents having to file a federal tax return; these rules are detailed in Publication 501, which the IRS provides.