A general rule of thumb is to refinance when interest rates drop 2 percentage points or more. For example, if you have a $100,000, 30-year, fixed-rate mortgage at 10 percent, you will pay more than $215,000 in interest over the next 30 years.umber of months. The number months you will be paying on your refinanced mortgage loan. 30 years = 360 months, 20 years = 240 months, 15 years = 180 months. Loan origination fee. This is a fee charged by the lender to evaluate, prepare and submit your loan. It typically ranges for 0.5% to 2%.