To determine if it makes good fianancial sense to refinance your existing mortgage at a lower interest rate or for different terms, just enter information about your existing mortgage (you can get this information off your most recent mortgage statement or by calling your lender) including the balance you owe of the principal, your current monthly payment and your current interest rate (example: for 7%, enter 7). Then enter the information about the refiancing you are considering. Then just click on the calculate button and results will show instantly. Try with different information as many times as you like. Not only will this calculator calculate the monthly payment and net interest savings, but it will also calculate how many months it will take to break even on the closing costs.