In Hutchinson v. Pennsylvania State Employes' Retirement Board, 738 A.2d 7 (Pa. Cmwlth. 1998), petition for allowance of appeal denied, 562 Pa. 676, 753 A.2d 821 (2000), the Court explained that interest is "impliedly payable as compensation to a creditor for delay of payment by the debtor whenever a liquidated, or fixed, sum of money is unjustly withheld." Id. at 12, quoting Braig v. Pennsylvania State Employes' Retirement Board, 682 A.2d 881, 886.
The two prerequisites to the running of interest, the Court said, were that "the debt must have been liquidated with some degree of certainty and the duty to pay it must have become fixed." Id.