The in-built calculator that comes with Windows 7 is new and improved with features not seen in previous versions.
One of this new features is the Worksheet feature which basically consists of few ready to use programs to calculate Mortgage,Vehicle Lease and Fuel Economy.
To use this first launch the calculator utility (Start > Run > calc.exe)
Go to View > Worksheets > Mortgage.
Select your payment plan and fill the corresponding values.
All done and in a jiffy too without using any external program 🙂