How to agree on a postjudgment interest rate

• This contract language binds the parties to an agreed-upon postjudgment interest rate: “All past due interest and/or principal shall bear interest from maturity until paid, both before and after judgment, at the rate of 9% per annum.”  The language “clearly, unambiguously, and unequivocally” refers to postjudgment interest.
• This language does not: “Invoices not paid within the stated terms will be charged 1.5% per month. . . .   All freight, demurrage and other charges shall be subject to an interest charge of 1-1/2% per month beginning on the first day after the due date of invoice.”

Celtic Marine Corp. v. James C. Justice Co., No. 13-31306 (Nov. 20, 2014, unpublished) (quoting Hymel v. UNC, Inc., 994 F.2d 260 (5th Cir. 1993) (emphasis added)).