The funds that the IDB lends are raised by selling bonds to institutional investors at standard commercial rates of interest. The bonds are backed by (a) the sum of the capital subscriptions actually paid in by the Bank's 47 member countries, plus (b) the sum of the callable capital subscriptions pledged by the Bank's 22 non-borrowing member countries. Together these constitute the Bank's "ordinary capital", some US$101 billion. Of this amount, 4.3 percent is paid in, while the remaining 95.7 percent is callable.