The following table (for 2017) on the minimum income to be declared applies to most working Americans:
If you work for yourself, or, say, received income from dividends, gratuities, royalties and the like, and it exceeds $ 400 (for the whole year), then you are also required to file a tax return.
In the USA, even the applicable tax rates depend on the status of a resident taxpayer, there are four categories of resident taxpayers:
1.) married persons who file a joint tax return;
2.) persons containing dependent family members;
3.) unmarried individuals
4.) married individuals submitting separate tax returns.