The interest rate that individuals will pay on underpayments remains at 3% for the first quarter of 2012. The interest rate that the IRS will pay on overpayments (tax refunds) will also be 3%. Most ordinary tax refunds do not earn interest. The IRS does not have to pay interest on tax refunds made within 45 days of the return
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.