<prompt> Human: I am thinking of selling a book on the Kindle store andor driving for Uber or Lyft to earn some extra money. I understand that I need to pay estimated quarterly taxes. Do I only have to pay on the non-W2 income, since I file a 1040 in April for that?  <response>: You can increase your federal withholding from your wages to cover the additional income and self employment tax liabilities. IRS Publication 505 is the primary written reference for Tax Withholding and Estimated Tax 