An adjustable rate mortgage is a mortgage loan that provides for the adjustment of its interest rate as market interest rates change. As the interest rate changes, the amount of the periodic payment changes to reflect the new interest rate. Given the terms of the original mortgage, the changes in the interest rate, and the time frame in which the changes occur, this procedure calculates the amount of each periodic payment. Once each payment is known, the Annual Percentage Rate (APR) of the entire transaction can be calculated.
Calculate the amount of the initial periodic payment.

Calculate the loan balance just before payments increase the first time, change the sign (CHS), and store the result in PV.

Change the interest rate, adjust the term, press 0, FV, and recalculate the periodic payment (PMT).

Calculate the loan balance before payments increase the next time, change the sign (CHS), and store the result in PV

Repeat steps 3 and 4 until all payments are calculated.

Once the payments are determined, use the cash flow keys and f, IRR to calculate the APR.