Question

in this web http://www.fonerbooks.com/interest.htm, it has example to calculate mortgage.

for example:
the loan = 100.000
interest 5%/year
payment : 12.000/month

we got this table (on the web, 3rd table)

Year     Principal       Interest    Payment
One     100,000     5,000           12,000
Two     93,000          4,650           12,000
Three   85,650          4,282.5     12,000
Four    77,932.5    3,896.63    12,000
Five    69,829.13   3,491.46    12,000
Six     61,320.58   3,066.03    12,000
Seven   52,386.61   2,619.33    12,000
Eight   43,005.94   2,150.3     12,000
Nine    33,156.24   1657.81     12,000
Ten     22,814.05   1,140.7     12,000 

My question:

• What is the formula for calculating
  interest in the X th year. For
  example: I want to know how much
  interest I have to pay in the seventh
  year.

• What is the formula for calculating from year x to y for
  example: I want to calculate sum of
  interest from first year to seventh
  year.

Answer 1

There are all sorts of formulae for mortgage calculations here.