The answer is: yearly earnings
From your yearly earnings, you would be placed on a specific income bracket. Each bracket has to pay the taxes based on different interest rates. (higher earning would means that you have to pay higher tax).
In united states, those income brackets are:
- 10% tax rate for those who earn between $0 to $9,275
- 15% tax rate for those who earn between $9,276 to $37,650
- 25% tax rate for those who earn between$37,650 to $91,150
- 28% tax rate for those who earn between $91,150 to $190,150