The amount of an overpayment or underpayment is the difference between the amount paid to the beneficiary and the amount of the payment to which the beneficiary was actually entitled. Such payment, for example, would be equal to the difference between the amount of a benefit in fact paid to the beneficiary and the amount of such benefit as reduced under section 202(j)(1), 202(k)(3), 203(a), or 224(a), or as increased under section 202(d)(2), 202(m), or 215 (f) and (g). In effecting an adjustment with respect to an overpayment, no amount can be considered as having been withheld from a particular benefit which is in excess of the amount of such benefit as so decreased.
20 C.F.R. §404.504