All home buyers should be concerned about getting the lowest possible mortgage rates on a new home purchase loan or a refinance loan. However, finding the rates to make the comparison is not always as easy as it may seem. A mortgage calculator can help you make an informed decision about your mortgage. Go to Guaranteed Rate to find a good option. The Guaranteed Rate's mortgage calculator is one of the easiest options to compare mortgage rates online and apply for preapproval at the same time.