Annualised return on an early payment discount

• The arithmeticThe buyer chooses between paying 98 on day 10 or 100 on day 30. Paying early costs 98 to save 2, a return of 2 over 98 for 20 days. Annualised that is 2 / 98 times 365 / 20, about 37.2 percent.
• On an invoice of 50,000Paying on day 10 costs 49,000 and saves 1,000. The buyer would need to earn more than 37 percent a year on that cash for refusing to make sense.