Note:

IRC 6621(c) doesn’t apply to individuals, trusts or "S" corporations.

The additional 2% interest only applies when the IRS issued a 30-Day or 90- Day Letter and only when the taxpayer hasn’t paid the amount due within 30 days of the 30-Day or 90-Day Letter date (whichever is issued first).

Ensure the additional 2% interest is assessed, enter the date the 30-Day or 90-Day Letter was issued (whichever is issued first) in the "2% interest date" : field on the "Individual/Bus. (1 of 3)" tab of RCCMS Closing Record.