Has anyone ever tried to use the mortgage worksheet? The calculations appear wrong. If you enter new mortgage principal (say, from a refi), and indicate that some of the money went towards buying, building, or improving an existing house, and some of the money did not, the program calculates a PERCENTAGE of the "qualified interest" which is deductible. However, this is NOT correct. See Publication 936, "mixed mortgages" or the IRS regulations. There is an ORDER in which mortgage interest must be deducted with mixed mortgage. The first type of interest would be home equity interest, that is, ANY interest from principal NOT used to buy, build, or improve. That includes things like buying a car, or even closing costs for the refi. (The closing costs were not used to build, buy, or improve the house. They were used typically to get you a better rate.) In other words, until you get rid of the home equity debt, you have a zero amount deduction on Schedule A. But the program does not do it that way.