5 CFR § 1315.17 - Formulas.
(a) Rebate formula.
(1) Agencies shall determine credit card payment dates based on an analysis of the total benefits to the Federal government as a whole. Specifically, agencies should compare daily basis points offered by the card issuer with the corresponding daily basis points of the government's Current Value of Funds (CVF) rate. If the basis points offered by the card issuer are greater than the daily basis points of the government” funds, the government will maximize savings by paying on the earliest possible date. If the basis points offered by the card issuer are less than the daily basis points of the government” funds, the government will minimize costs by paying on the Prompt Payment due date or the date specified in the contract.
(2) Agencies may use a rebate spreadsheet which automatically calculates the net savings to the government and whether the agency should pay early or late. The only variables required for input to this spreadsheet are the CVF rate, the Maximum Discount Rate, that is, the rate from which daily basis points offered by the card issuer are derived, and the amount of debt. This spreadsheet is available for use on the prompt payment website at www.fms.treas.gov/prompt/index/.html.
(3) If agencies chose not to use the spreadsheet, the following may be used to determine whether to pay early or late. To calculate whether to pay early or late, agencies must first determine the respective basis points. To obtain Daily Basis Points offered by card issuer, refer to the agency's contract with the card issuer. Use the following formula to calculate the average daily basis points of the CVF rate:
(4) For example: The daily basis points offered to agency X by card issuer Y are 1.5 basis points. That is, for every day the agency delays paying the card issuer the agency loses 1.5 basis points in savings. At a CVF of 5 percent, the daily basis points of the Current Value of Funds Rate are 1.4 basis points. That is, every day the agency delays paying, the government earns 1.4 basis points. The basis points were calculated using the formula:
(5) Because 1.5 is greater than 1.4, the agency should pay as early as possible. If the basis points offered by the card issuer are less than the daily basis points of the government” funds (if for instance the rebate equaled 1.3 basis points and the CVF was still 1.4 basis points or if the rebate equaled 1.5 but the CVF equaled 1.6), the government will minimize costs by paying as late as possible, but by the payment due date.
(b) Daily simple interest formula.
(1) To calculate daily simple interest the following formula may be used:
(2) For example, if a payment is due on April 1 and the payment is not made until April 11, a simple interest calculation will determine the amount of interest owed the vendor for the late payment. Using the formula above, at an invoice amount of $1,500 paid 10 days late and an interest rate of 6.5%, the amount of interest owed is calculated as follows:
(c) Monthly compounding interest formula.
(1) To calculate interest as required in § 1315.10(a)(3), the following formula may be used:
(2) The first part of the equation calculates compounded monthly interest. The second part of the equation calculates simple interest on any additional days beyond a monthly increment.
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