Penalty

The IRS penalizes you for lateness whether you failed to pay the entire tax or underpaid it. Whatever amount you still owe after April 15 incurs a penalty.

Calculating the Penalty

The usual penalty accumulates at the rate of 0.5 of 1 percent of the unpaid amount for each month or portion of a month as long as the amount is not paid. The maximum penalty is 25 percent.

Estimated Tax Penalty

If you pay quarterly estimated taxes, underpayment carries a different penalty. Form 2210 tells whether to figure this penalty using the "short" or "regular" method. Both multiply the overdue amount by rates that change every year. The regular method also multiplies by the number of days that each quarterly payment is overdue. If you qualify to use the short method, you can deduct from the penalty if you pay before a quarterly deadline.

Corporate Income Tax Penalty

If you are a corporation, underpaying your income tax incurs similar penalties to those incurred by individuals, including estimated tax penalties figured on Form 2220.

Contact the IRS

To contact the IRS call (800) 829-1040 or access irs.gov to find particular phone numbers.

Source:

Tax Topic 653: IRS Notices and Bills, Penalties and Interest Charges

Tax Topic 306: Penalty for Underpayment of Estimated Tax

IRS Publication 542: Corporations (See "Penalties")

Resource:

Internal Revenue Service