Fixed Loan, ARM loan? What the heck I just want to buy a house! But it is important for you to understand the difference in these two types of loans. A Fixed loan will have one mortage payment (based on current interest rates) for the life of the loan. An ARM (adjustable rate mortgage) will have a payment that varies based on the interest rate on the date that the loan is recalculated each year. If mortgage rates go up you pay more. If they go down you pay less. With this type of loan you are gambling that rates will not go up 'too' much. This calculator allows you to see for different types of loan and different guesses about future interest rates how your payment might vary.