Retirement Inflation Protection Act of 2021 This bill allows the adjusted basis of certain assets, including C corporation common stock and tangible property used in a trade or business, to be adjusted for inflation solely for the purpose of determining the gain or loss of individuals who (1) have held such assets for more than 3 years, and (2) have attained the age of 59 1/2 as of the date of the sale or other disposition of the assets. The bill uses the Chained Consumer Price Index for All Urban Consumers (C-CPI-U) for purposes of making the inflation adjustment. The bill sets forth rules for applying the inflation adjustment to short sales, dispositions between related persons, and improvements to property. The Internal Revenue Service may disallow an adjustment if any person transfers cash, debt, or any other property to another person for the principal purpose of securing or increasing an inflation adjustment.