Charges/fee on underutilized credit line

Hi ,

I would like to calculate the charges/fee (percentage or amount)  based underutilized facility amount.

Ex: Company has credit limit of 200 Billions with bank.On month end company utilized 160 Billions(borrowed from bank).But company has to pay margin fee/interest (ex: 0.5%) to bank on underutilized 40 Billions. In general, system should able to recognize the interest rates based on utilization of facility.If the utilization of facility is less than 40% of total credit line the interest is 0.75%, and utilization level is > 40% and < 80%, interest rate is 0.5% and more than 80% utilization, the interest rate is 0.25%.

Thanks,