How do I calculate and submit payment for penalties and interest on an amended individual return, Form 1040X?
There is no line on Form 1040-X on which to enter penalties or interest to be calculated and sent with the amended return. Any additional tax due is shown on line 20 of Form 1040-X as Amount you owe. This amount does not take into account any possible interest or penalties. The IRS will review the amended return once received and issue a notice of the penalties and interest due on that amount. Include the amount to be paid with the paper-filed amended return by check or money order, or go online to 1040paytax.com to submit the payments electronically. Per the 1040-X Instructions:
"The IRS will charge you interest on taxes not paid by
their due date, even if you had an extension of time to file. The
IRS will also charge you interest on penalties imposed for failure
to file, negligence, fraud, substantial valuation misstatements,
substantial understatements of tax, and reportable transaction
understatements. Interest is charged on the penalty from the due
date of the return (including extensions).
If you don’t pay the additional
tax due on Form 1040X within 21 calendar days from the date of
notice and demand for payment (10 business days from that
date if the amount of tax is $100,000 or more), the penalty is
usually 1/2 of 1% of the unpaid amount for each month or part of a
month the tax isn’t paid. The penalty can be as much as 25% of
the unpaid amount and applies to any unpaid tax on the return.
This penalty is in addition to interest charges on late payments.
You won’t have to pay the penalty if you can show reasonable
cause for not paying your tax on time."
See Publication 17 for additional information.