Investors who plan to reinvest periodic interest (or "coupon") payments face uncertainty because the returns (interest rates) at which those cash flows will be reinvested cannot be known at the time of the initial purchase. If market rates of interest decrease after the initial investment is made, reinvestment risk works against the security holder, since future interest payments to the investor will be reinvested at a lower return than expected when the bond was purchased. As finance scholar Dr. Annette Thau has observed, the use of the term "risk" in this case is not quite correct because there is no actual risk of loss, either of principal or interest. "But... if you reinvest coupons at a lower rate than the [yield to maturity] quoted to you [when the bond was bought], actual return will then be lower than the
yield to maturity quoted to you when you bought the bond." When interest rates rise, reinvestment risk works in the security holder's favor because cash flows received can be reinvested in higher-yielding securities. Reinvestment risk and
interest rate risk have offsetting effects: higher market rates decrease the market value of the bond, but increase the interest earned on reinvested coupons. A bond portfolio strategy known as
immunization takes advantage of these offsetting effects. As Thau and finance scholar
Dr. Frank Fabozzi have observed, securities with a longer term to maturity carry greater reinvestment risk. The same is true of bonds with high coupon rates.
Zero-coupon bonds, which are issued by the
U.S. Department of the Treasury, have no coupon reinvestment risk because they have no periodic coupon payments, interest being paid in full when the bond matures. Reinvestment risk is particularly important for
mortgage-backed securities, because payments are received as frequently as every month. Bonds purchased at a premium are more susceptible to reinvestment risk than discount bonds. For investors who plan to spend, rather than invest, a security's cash flows, reinvestment risk may not be an issue. == Pension funds ==