You'll need to keep detailed records of your adjusted basis for noncovered shares, including adjustments made for purchases and sales of mutual funds, most exchange - traded funds (ETFs), and stocks. (investor.vanguard.com)
Cost basis for sales of noncovered shares will be reported solely to you. (investor.vanguard.com)
Both of these provisions are intended to adjust for a perceived unfair advantage when Social Security benefit formulas are applied to those who also earned pensions in noncovered employment. (cfs4me.com)