Selling Your Home - Capital Gains Tax on the Sale of a Main Home How to calculate capital gains taxes on the sale of a main home. Plus tips for lowering your capital gains using the Section 121 capital gains exclusion when selling your principal residence. How to calculate capital gains taxes on the sale of a main home. Plus tips for lowering your capital gains using the Section 121 capital gains exclusion when selling your principal residence. homesaletax with buyingcalculatecapitalgainshousesalesellingtaxesby 2 users