<prompt> Human: Is there any interest accrued on the difference between the amount that one has to pay for taxes in April and the amount that wasnt withheld during the previous year? If not, its essentially a zero interest loan from the government for 12-16 months, correct? Is there any reason not to set all my withholdings to zero, collect that difference and invest it, then pay the full taxes owed in April?  <response>: You can definitely under-withhold I do, but if you under-withhold too much, you have to pay a penalty when you file. Figuring out where that line is is complicated, but not withholding anything would certainly meet it. 