How Does the IRS Calculate Penalties and Interest?Late payment of employment taxes will trigger penalties and interest charges to the taxpayer. These notices, particularly from the IRS, are next to impossible to decipher. Here is a quick primer on IRS penalty and interest calculations.Statue of LimitationsThere is NO statue of limitations on the failure to file and report payroll taxes (Social Security, Medicare, Unemployment, withheld income taxes). There also is no statue of limitations on assessment of tax, penalties and interest when a false tax return is filed. Household employment taxes are remitted with the employer's personal income tax return. Any household employer who did not pay these taxes has de jure submitted a false tax return.Penalty Charges-- Late Filing PenaltiesIf you owe tax and don't file on time, according to IRS regulations, penalties are assessed and added to your bill. Penalties are in addition to BOTH the tax due and the interest on the past due tax. The total late–filing penalty is usually 5% of the tax owed for each month, or part of a month, that your return is late up to five months (25%). If your return is over 60 days late, the minimum penalty for late filing is the smaller of $100 or 100 percent of the tax owed.-- Late Payment PenaltiesIf you file on time but don't pay all amounts due on time, you'll generally have to pay a late payment penalty of one–half of one percent (0.5%) of the actual tax owed for each month, or part of a month, that the tax remains unpaid from the due date, until the tax is paid in full. There is no maximum limit to the failure-to-pay penalty.Interest ChargesThe IRS will charge interest on late or unpaid taxes, regardless of cause. The period covered always begins with the due date of the return, and ends with the receipt of payment by the IRS. You may incur interest expenses for late filing, or simply for making a mathematical error on your tax return.Generally, interest is charged on any unpaid tax from the due date of the return until the date of payment.The interest rate on unpaid Federal tax is determined and posted every three months. It is the federal short–term interest rate plus 3 percent. Interest is compounded daily.Jan. 1, 1992--Mar. 31, 19928%Apr. 1, 1992--Sep. 30, 19927%Oct. 1, 1992--Jun. 30, 19946%Jul. 1, 1994--Sep. 30, 19947%Oct. 1, 1994--Mar. 30, 19958%Apr. 1, 1995--Jun. 30, 19959%Jul. 1, 1995--Jun. 30, 19968%Jul. 1, 1996--Mar. 31, 19988%Apr. 1, 1998--Mar. 31, 19997%Apr. 1, 1999--Dec. 31, 19998%Jan. 1, 2000--Mar. 31, 20008%Apr. 1, 2000--Mar. 31, 20019%Apr. 1, 2001--Jun. 30, 20018%Jul. 1, 2001--Dec. 31, 20017%Jan. 1, 2002--Dec. 31, 20026%Jan. 1, 2003--Sep. 30, 20035%Oct. 1, 2003--Mar. 31, 20044%Apr. 1, 2004--Jun. 30, 20045%Jul. 1, 2004--Sep. 30, 20044%Oct. 1, 2005--Mar. 30, 20055%Apr. 1, 2005--Sep. 30, 20056%Oct. 1, 2005--Dec. 31, 20057%Jan.. 1, 2006--Mar. 31, 20067%Apr. 1, 2006--Jun. 30, 20067%July 1, 2006--Sept. 30, 20068%Oct. 1, 2006--Dec. 31, 20068%Jan. 1, 2007--Mar. 31, 20078%Apr. 1, 2007--Jun. 30, 20078%July 1, 2007--Sept. 30, 20078%Oct. 1, 2007--Dec. 31, 20078%Jan. 1, 2008--Mar. 31, 20087%Apr. 1, 2008--Jun. 30, 20086%July 1, 2008--Sept. 30, 20085%Oct. 1, 2008--Dec. 31, 20086%