P - Principal, the sum of money lent or borrowed.
R - Rate of interest: Annual interest, often expressed as a percentage.
T - Time period for which the money is lent or borrowed.
Simple Interest = Principal * Time * Rate of interest / 100
SI = P * T * R
For example, Principal is 4000, Rate of Interest is 8% and Time period is 4 years
SI = 4000× 8% × 4 = 4000× 0.08 × 4
In compound interest, the principal amount with interest after the first time period becomes the part of principal for the next time period.
CI = [P (1 + R/100)^T] – P
Total amount = [P (1 + R/100)^T]
If time period is half-yearly,
Amount = P[1 + (R/2)/100]^2T
If time period is quarterly,
Amount = P[1 + (R/4)/100]^4T
For example, Principal is 7500, Rate of Interest is 4% (compounded annually) and Time period is 2 years
Total Amount = [7500×(1+4/100)^2] = 8112.
CI = (8112 - 7500) = 612.