Stock Buyback Accountability Act of 2021 This bill imposes a 2% excise tax on the value of any stock of certain publicly-traded domestic and foreign corporations repurchased (i.e., redeemed) by such corporations. The bill allows exemptions from the tax for repurchases that are part of a reorganization, for repurchased stock that is contributed to an employer-sponsored retirement plan or employee stock ownership plan, for repurchased stock whose value does not exceed $1 million, and for repurchases treated as dividends.