The interest rates paid on overpayments and underpayments remain the same in the fourth quarter of 2010 as they have been all year. Individuals will pay 4% on underpayments and receive interest of 4% on overpayments during this period. This rate has been in effect since April 1, 2009.
Source: Rev. Rul. 2010-21; 2010-39 IRB 1
Advance payment of current tax liability based either on wage withholdings or installment payments of your estimated tax liability. To avoid penalties, you generally must pay to the IRS either 90% of your final tax liability, or either 100% or 110% of the prior year’s tax liability, depending on your adjusted gross income.