What is the minimum wage earnings to file an income tax?

As I, a non-professional understand it: $3,300 is the minimum to have to file if you work for an employer and get a W2. $400 is the minimum if you're self employed. Also, if you're getting a tax refund, you MUST file. Most people advise filing taxes every year, even if you income is super-low, so that the IRS never has any extra reason to audit you.