In order to add the cost of capital improvements (an addition on the home, a new furnace or roof) to your basis, you need documentation. If you don’t have receipts for your expenditures, try getting what you need in another way. For example, contact the contractor or vendor you used for a sprinkler system, new carpeting, or any other improvement and ask for a copy of a paid receipt.
This is generally adjusted gross income increased by certain items such as tax-free foreign earned income. MAGI usually is used to determine phaseouts of certain deductions and credits.