# Knowledge Base

## Solution 11206: Calculating Summed Interest and Principal on the BA-35 Solar.

### How are summed interest and principal calculated on the BA-35 Solar?

The following example demonstrates how to calculate summed interest and principal on the BA-35 Solar.

Example:
16 payments have been made on a mortgage thus far.  The original mortgage amount was $68,499.57 to be paid over 30 years, with an annual interest rate of 13.25% compounded monthly. Monthly payments are$771.15.  What is the summed interest and principal of payments 5 through 16?

Solution:
• Press [AC/ON] [CE/C] [2nd] [CMR] to clear the calculator's memory.
• Press [2nd] [FIX]  to fix the decimal places setting to two places.
• If 'FIN' is not displayed in the bottom-left corner, press [MODE] until it is.
• If 'Begin' is displayed, press [2nd] [BGN] so that it's not.
• Input 68499.57, then press [PV]. -  68499.57 is stored to the present value (PV) register.
• Input 13.25, then press [2nd] [÷12] to convert to a monthly rate, then press [%i] - 13.25 is stored to the interest rate (%i) register.
• Input 30, then press [2nd] [×12] to convert the number of annual payments to monthly payments, then press [N] - 30 (years) is converted to 360 (months), and that value is stored to the term length (N) register.
• Input 771.15, then press [PMT] - 771.15 is stored to the payment (PMT) register.
• Input the number for the beginning payment, 5 in this case, then press the [P1/P2] key.
• Input the number for the ending payment, 16 in this case, then press [I/P] to calculate the summed interest - the result of 9,056.52 is displayed.
• Press the [xÛy] key to display the summed principal - the result of 197.28 is displayed.