Individual income tax is imposed on the worldwide-sourced income of U.S. citizens or residents, and on the domestic-sourced income of U.S. non-residents. According to the IRS, not everyone is obligated to file a tax return, such as in situations below the standard deduction. The following article will provide a brief overview of who is required to file a U.S. individual income tax return.

1. General rule and deduction
   
   Depending on the situation, a tax return must be filed when the income is equal to or greater than the following criteria.
   
   (1) Single or married filing separately must file when income equal to or greater than $12,950. Available additional deductions can be increased by $1,750.
   
   (2) Head of Household must file when income equal to or greater than $19,400. Available addition deductions can be increased by $1,750.
   
   (3) Married filing jointly and surviving spouses must file when income equal to or greater than $25,900. Available additional deductions can be increased by $1,400.
   
   The above figures are adjusted annually for inflation. Additional deductions are available for taxpayers who are blind and 65 years of age or older.
   
   
2. The following exceptions also require filing a tax return
   
   (1) Individuals with net income of $400 or more from self-employment must file.
   
   (2) Taxpayers who are married and have another dependent with unearned income of more than $1,150.
   
   (3) Individuals with income or tax liability under Section 965.
   
   (4) Individuals who received money from medical savings account during the year.
   

Reference:
https://www.irs.gov/newsroom/who-needs-to-file-a-tax-return
https://www.irs.gov/individuals/check-if-you-need-to-file-a-tax-return
https://www.irs.gov/forms-pubs/about-form-1040
https://www.irs.gov/filing/taxable-income