Calculate Simple Interest, Principal, Rate or Time when 3 Values are Known

Let's say you want to borrow $6300.00 from March 15th, 2004 until January 20th 2005 at a rate of 8%. The formula will still be I = Prt, however, you need to calculate the days. To do so, you will not count the day the money is borrowed or the day the money is returned. Let's figure out the days: March = 16, April = 30, May = 31, June = 30, July = 31, August = 31, September = 30, October = 31, November = 30, December = 31, January = 19. Therefore the time is 310/365. A total of 310 days out of 365. This is entered into the t for the formula.