In addition, the purchase programs have affected the duration of the portfolio. The securities that have been purchased by the Desk since November have had an average duration of about 5.5 years. With those purchases and the adjustments from the earlier purchase programs, the duration of the overall SOMA portfolio has reached about 4.5 years, which is somewhat higher than the typical level of between 2 and 3 years that was observed before the financial crisis. This combination of its larger size and longer duration results in a greater amount of interest rate risk embedded in the SOMA portfolio. 13 Of course, under the view that the asset purchase programs operate through a portfolio balance channel, this is precisely how the programs have an effect on the economy – by transferring risk away from private investors and onto the Fed’s books. The risks to the portfolio arise because the characteristics of the assets that have been purchased differ from those of the liabilities that have been created by those purchases. The assets held in the SOMA portfolio have fixed coupon rates that reflect longer-term interest rates. However, the purchases of those assets create reserves in the banking system, and the Federal Reserve pays interest on those reserves at a short-term interest rate that it  13  Note that the securities purchased under these programs involve no credit risk, given that they are issued by the Treasury or are guaranteed by government sponsored enterprises.
The relevant risk for the SOMA portfolio instead has to do with movements in interest rates at different maturities. BIS central bankers’ speeches  5  controls. The interest paid on reserves can be thought of as the “funding cost” of the portfolio. Today, because short-term interest rates are low relative to longer-term interest rates, this mismatch produces a very elevated stream of net income. In particular, the SOMA portfolio has a weighted average coupon yield of about 3.5 percent, which, if applied to a $ trillion portfolio, produces about $ billion of income at an annualized rate. 14 In contrast, the annualized funding cost of the portfolio at this time is only around $ billion. This cost is relatively low because of the near-zero level of the interest rate paid on reserves. In addition, the private sector holds nearly $ trillion of currency, which are liabilities of the Federal Reserve that bear no interest. 15 Thus, the SOMA portfolio should produce a considerable amount of net income over the near term. 16 Beyond the near term, though, the income that will be produced by the SOMA portfolio is uncertain. If short-term interest rates were to rise, the funding cost of the portfolio would increase relative to the fairly steady yield earned on the assets held, reducing the amount of net income from the portfolio. In addition, if longer-term yields were to shift higher, the Federal Reserve could realize capital losses if it were to begin selling assets.