5 CFR § 1315.7 - Discounts.
(a) Economically justified discounts. If an agency is offered a discount by a vendor, whether stipulated in the contract or offered on an invoice, an agency may take the discount if economically justified (see discount formula in Treasury Financial Manual (TFM) 6-8040.40) 3 but only after acceptance has occurred. Agencies are encouraged to include discount terms in a contract to give agencies adequate time to take the discount if it is determined to be economically justified.
3 The Treasury Financial Manual is available by calling the Prompt Payment Hotline at 800-266-9667 or the Prompt Payment web site at http://www.fms.treas.gov/prompt/index.html.
(b) Discounts taken after the discount date. If an agency takes the discount after the deadline, the agency shall pay an interest penalty on any amount remaining unpaid as prescribed in § 1315.10(a)(6).
(d) Start date. The period for taking the discount is calculated from the date placed on the proper invoice by the vendor. If there is no invoice date on the invoice by the vendor, the discount period will begin on the date a proper invoice is actually received and date stamped or otherwise annotated by the designated agency office.