Capital gains is very complicated, since it depends on your "basis" in the house, which is a factor of what you paid for it and certain renovations to or investments in the home you make, which increase the basis. Essentially and to oversimplify, capital gains is what you actually realize on the home less the basis; that is the amount taxed as capital gains. Additional complications include that the proceeds from a home are treated differently if your roll them into buying a new home vs. pocket the money. If you have a $25,000,000 home to sell as you write, it would be well worth your time to consult with a CPA about your taxes and how to minimize them.