Why a penalty appears even when you paid
The federal system is pay-as-you-go. Wages usually have tax withheld, but income from self-employment, investments, rental property, or the sale of an asset may not, and a large bonus can come with too little withholding, so the IRS expects estimated payments through the year. If too little is paid by an installment date, a penalty is figured on the shortfall for the time it was outstanding, much like interest, at a rate the IRS sets and adjusts periodically. This penalty is separate from the failure-to-pay penalty for not paying the balance by the return deadline, and separate from accuracy-related penalties for understating tax on a return. A notice sometimes shows more than one.
Safe harbors and ways to reduce it
Taxpayers can usually avoid the penalty by paying, through withholding and estimates, at least an amount based on the prior year's tax or most of the current year's tax, with a higher prior-year target for higher incomes. Withholding is generally treated as paid evenly through the year even if it happened late, so increasing withholding toward year-end can help in a way that a late estimated payment cannot. If your income arrived unevenly, such as a large gain late in the year, the annualized income method can reduce or remove the penalty for earlier installments. These calculations are made on the IRS form for underpayment of estimated tax, filed with the return.
Waivers and next steps
First time abatement does not apply to this penalty, but the IRS can waive it when the underpayment was caused by a casualty, disaster, or other unusual circumstance that would make the penalty inequitable, and in some cases for taxpayers who retired after reaching a certain age or became disabled in the year or the year before and had reasonable cause. Farmers and fishermen follow their own payment rules. If you receive a notice, check whether the IRS applied all of your payments to the right year, since misapplied estimates are a common cause. We review the payment history and the calculation and, where it makes sense, help adjust the coming year's withholding or estimates.
