供樓銀行利息計算公式

For your case, L - P. I dont know whether it is correct or not as I learnt it from 15 years ago from school.
Suppose L= Lump sum paymenis including interst payment and princple = M x total no. of instalments, P = princple, M = Monthly instalment, r = monthy interest rate = R/12monts, R = annual interest rate and n = total no of instalments

M formula = {P x ( 1 + r)n x r} / { (1+ r)n - 1 }

For your case, P = $600,000, n = 240 ( 20 years equal to 240 months), R = 4,8%, r = 0,004,
However, M = {$600,000 x (1+ 0,004)240 x 0,004} / { (1 + 0,004)240 - 1}
= {600,000 x 2.6067 x 0,004} / {2.6067 - 1}
= 6256.08 / 1.6067
Monthly instalments = $3,893,7

L = M x n
= 3,893,7 x 240 instalments
= $934,498,8

Z = L - P
= 934,498,8 - 600,000
= $334,498

Therefore, the total interest will pay for this Mortage after 20 years is HKD 334, 498.

I hope it will assist you.
Felix

2.6067 怎樣計算出來的