General rule. Effective for interest accruing after December 31, 1982, in computing the amount of any interest required to be paid under the Internal Revenue Code of 1954 or sections 1961(c)(1) or 2411 of title 28, United States Code, by the Commissioner or by the taxpayer, or in computing any other amount determined by reference to such amount of interest, or by reference to the interest rate established under section 6621, such interest or such other amount shall be compounded daily by dividing such rate of interest by 365 (366 in a leap year) and compounding such daily interest rate each day.

Exception. Paragraph (a) of this section shall not apply for purposes of determining the amount of any addition to tax under sections 6654 or 6655 (relating to failure to pay estimated income tax).

Applicability to unpaid amounts on December 31, 1982—(1) In general. The unpaid interest (or other amount) that shall be compounded daily includes the interest (or other amount) accrued but unpaid on December 31, 1982.

Illustration. The provisions of this (c) may be illustrated by the following example.

Individual A files a tax return for calendar year 1981 on April 15, 1982, showing a tax due of $10,000. A pays $10,000 on December 31, 1982, but A does not pay any interest with respect to this underpayment until March 1, 1983, on which date A paid all amounts of interest with respect to the $10,000 underpayment of tax. On December 31, 1982, A's unsatisfied interest liability was $1,424.66 ($10,000 × 20 percent × 260/365 days). Interest, compounded daily, accrues on this unsatisfied interest obligation beginning on January 1, 1983, until March 1, 1983, the date the total interest obligation is satisfied. On March 1, 1983, the total interest obligation is $1,462.62, computed as follows: