In any case in which an operator fails to pay benefits that are due (§ 725.502), the beneficiary shall also be entitled to simple annual interest, computed from the date on which the benefits were due. The interest shall be computed through the date on which the operator paid the benefits, except that the beneficiary shall not be entitled to interest for any period following the date on which the beneficiary received payment of any benefits from the fund pursuant to § 725.522.

In any case in which an operator is liable for the payment of retroactive benefits, the beneficiary shall also be entitled to simple annual interest on such benefits, computed from 30 days after the date of the first determination that such an award should be made. The first determination that such an award should be made may be a district director's initial determination of entitlement, an award made by an administrative law judge or a decision by the Board or a court, whichever is the first such determination of entitlement made upon the claim.

In any case in which an operator is liable for the payment of additional compensation (§ 725.607), the beneficiary shall also be entitled to simple annual interest computed from the date upon which the beneficiary's right to additional compensation first arose.

In any case in which an operator is liable for the payment of medical benefits, the beneficiary or medical provider to whom such benefits are owed shall also be entitled to simple annual interest, computed from the date upon which the services were rendered, or from 30 days after the date of the first determination that the miner is generally entitled to medical benefits, whichever is later. The first determination that the miner is generally entitled to medical benefits may be a district director's initial determination of entitlement, an award made by an administrative law judge or a decision by the Board or a court, whichever is the first such determination of general entitlement made upon the claim. The interest shall be computed through the date on which the operator paid the benefits, except that the beneficiary or medical provider shall not be entitled to interest for any period following the date on which the beneficiary or medical provider received payment of any benefits from the fund pursuant to § 725.522 or subpart I of this part.

If an operator or other employer fails or refuses to pay any or all benefits due pursuant to an award of benefits or an initial determination of eligibility made by the district director and the fund undertakes such payments, such operator or other employer shall be liable to the fund for simple annual interest on all payments made by the fund for which such operator is determined liable, computed from the first date on which such benefits are paid by the fund, in addition to such operator's liability to the fund, as is otherwise provided in this part. Interest payments owed pursuant to this paragraph shall be paid directly to the fund.

In any case in which an operator is liable for the payment of an attorney's fee pursuant to § 725.367, and the attorney's fee is payable because the award of benefits has become final, the attorney shall also be entitled to simple annual interest, computed from the date on which the attorney's fee was awarded. The interest shall be computed through the date on which the operator paid the attorney's fee.

The rates of interest applicable to paragraphs (a), (b), and (c) of this section shall be computed as follows:

For all amounts outstanding prior to January 1, 1982, the rate shall be 6% simple annual interest;

For all amounts outstanding for any period during calendar year 1982, the rate shall be 15% simple annual interest; and

For all amounts outstanding during any period after calendar year 1982, the rate shall be simple annual interest at the rate established by section 6621 of the Internal Revenue Code (26 U.S.C.) which is in effect for such period.

The fund shall not be liable for the payment of interest under any circumstances, other than the payment of interest on advances from the United States Treasury as provided by section 9501(c) of the Internal Revenue Code (26 U.S.C.).