US mortgage calculator with amortization schedule - help

This JavaScript mortgage calculator is designed to calculate 2 type of requests:

1. Your periodic payment or
2. The principal amount you can borrow

At the same time, this calculator will show you the amortization schedule of the loan.

Enter the outstanding loan balance — the principal (1)
Enter the interest rate — annual rate in percentage (2)
Enter the amortization period in months — how long until you repay
Enter the payment type (annual, semi-annual, monthly, bi-weekly, weekly, accelerated bi-weekly or accelerated weekly)
Click on "Calculate Payment" to see what your periodic payments will be — answer shows in (6)

Enter the interest rate — as an annual percentage (2)
Enter the amortization period in months (how much time is the loan for (3)
Enter the payment type (annual, semi-annual, monthly, bi-weekly, weekly, accelerated bi-weekly or accelerated weekly) (4)
Enter the desired periodic payment (6) (how much you want your periodic payments to be)
Click on "Calculate Principal" (7) to see how much you will be able to borrow — answer shows in (1)

Click on the image to use this amortization calculator

An amortization schedule is a timetable for payments of a mortgage loan. This calculator's amortization schedule (8) table shows:

the payment number,
the Principal Balance owed before the periodic payment,
the amount of the payment that is applied to repay the Principal (Capital Paid),
the Total Capital paid up to that periodic payment,
the amount of the payment that is applied to pay the interest (interest Paid),
the Total interest paid up to that periodic payment.