In the United States, individuals must file income taxes if their income exceeds a certain threshold based on their filing status, age, and income sources. As of the 2021 tax year, the income thresholds for most people are as follows: - Single individuals under the age of 65: Must file if their income is at least $12,550. - Married individuals filing jointly under the age of 65: Must file if their combined income is at least $25,100. - Head of household under the age of 65: Must file if their income is at least $18,800. - Married individuals filing separately: Must file if their income is at least $5. - Self-employed individuals with a net earnings of $400 or more. These thresholds can change each year, so it is important to refer to the current tax laws for the applicable year. Additionally, there may be other factors that can affect the filing requirements, such as receiving certain types of income or claiming specific credits or deductions.