利率複式及按揭計算

利率複式計算 Compound interest

A = (P1+P) m^k + P m (m^k-1-1)/(m-1)]

Where     A     = total amount after t year
                P1    = Principal amount
                P      = addition per times
                n      = number of times interest per annual
m     = (1+ r/n)
k      = nt
r       = annual interest rate
Compound interest calculator
http://www.moneychimp.com/calculator/compound_interest_calculator.htm

按揭計算 Mortgage
Monthly payment,    P = P1 m^k (m-1) / (m^k-1)

Where      P1    = Principal amount
m     = (1+ r/n)
t       = number of year
k      = nt
r       = annual interest rate

Mortgage Calculator

http://www.property.hk/Mortgage/index.cni