mortgage 利息點計???

Principal (P) = HK$1,000,000.00
no. of period (n) = 20yrs x 12 months / yr = 240 periods (assume monthly payment)
effective interest rate per period (i) = 5% p.a. / 12 = 0.417%

regular / monthly payment (R) = (P x i) / {1 - [(1 + i) ^ (-n)]} = HK$6,599.56

at the end of period 1:
You have to pay out R = HK$6,599.56
in which,
interest payment = HK$1,000,000.00 x i = HK$4166.67
principal repayment = R - interest payment = HK$2,432.89
Now, the outstanding balance = HK$1,000,000.00 - principal repayment = HK$997,567.11

at the end of period 2:
You have to pay out R = HK$6,599.56
in which,
interest payment = HK$997,567.11 x i = HK$4156.53
principal repayment = R - interest payment = HK$2,443.03
Now, the outstanding balance = HK$997,567.11 - principal repayment = HK$995,124.08

and so forth

http://202.72.14.202/mortgage/calc.asp

http://www.centanet.com/chome.htm

這裡可以幫到你