Because you acquired the home by a gift, your basis usually is the basis that your parents had in the home (what they paid for it, plus capital improvements they made over the years). It may be difficult to reconstruct this information, but their initial cost may be available (e.g., published on Zillow).
A tax technique for receiving a refund of back taxes by applying a deduction or credit from a current tax year to a prior tax year. For example, a business net operating loss may be carried back for two years.