Determine the annual interest rate, compounding frequency, length of the loan in years and the amount you borrowed. For the purpose of an example, assume a loan of $4,000 at a 10 percent annual interest rate that will be repaid in three years with monthly interest calculation (compounding).
Enter the figures into a compound interest formula. The formula is A = P (1+r/c)^c*n, where A equals the total amount you owe, P is the principal amount you borrowed, r is the rate, c is the number of times the loan interest gets calculated each year (compounding) and n is the number of years you'll take to repay the loan.
Calculate the total amount you owe --- you'll need a calculator that performs exponential calculations. So in this instance, the filled formula is A (total amount you owe) = 4,000 (1+.10/12)^12*3, or about $5,393.