Formula:

Total Amount = Principal + CI (Compound Interest)

a. Formula for Interest Compounded Annually
         Total Amount = P(1+(R/100))ⁿ

b. Formula for Interest Compounded Half Yearly
         Total Amount = P(1+(R/200))²ⁿ

c. Formulae for Interest Compounded Quarterly
         Total Amount = P(1+(R/400))⁴ⁿ

d. Formulae for Interest Compounded Annually with fractional years (e.g 2.5 years)
         Total Amount = P(1+(R/100))^a×(1+(bR/100))
         here if year is 2.5 then a =2 and b=5

e. With different interest rates for different years
Say x% for year 1, y% for year2, z% for year3
         Total Amount = P(1+(x/100))*(1+(y/100))*(1+(z/100))

where CI = Compound Interest, P = Principal or Sum of amount, R = % Rate per annum, n = Time Span in years

Online Compound Interest Calculation. Calculating Compound Interest, Principal, different Rate of Interest for Annual, Half yearly, Quartely and for Fractional Years is made much easier.