Banks that are members of the Federal Reserve System make payments for Federal Reserve Bank capital stock. Each member is required by law to become a shareholder and subscribe to shares of its district Reserve Bank in an amount equal to 6 percent of its own paid-in capital and surplus. Of this amount, half must be paid to the Federal Reserve and half remains subject to call by the Board of Governors. When a member's capital or surplus changes, its holdings of Reserve Bank stock must be adjusted accordingly.
Board of Governors of the Federal Reserve System (US), Capital - Capital Paid in [WCPIL], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/WCPIL/, October 13, 2015.