HINT: By selecting annual compounding and fiddling with the monthly payments one can use the program to calculate how much to stash away each month so that you know how much your retirement nest egg will be in 30 years. The initial Principal selected is not important, you let it (principal) vary so that you can pick the appropriate interest rate with annual compounding and choose the amount of monthly contribution (which would normally be your mortgage payment) and calculate the accumulation for the next 30 years.
EXAMPLE: Lets say you wanted to put away $1000 per month for 30 years growing at 12% per year (a conservative mutual fund) and find out how much it would be worth at the end of 30 years. Change the compounding to annual, enter 12%, 30 years for the amortization period and $1000 per month as the payment. The Principal will be automatically calculated as $101,869.87 Forget about the principal as it means nothing once the payments are changed to zero inside the SPREADSHEET/amortization schedule.