When thinking about how to generate returns within a bond portfolio It is first important to consider the various different components of return that you might get from a bond. These include the income return from a bond's coupon, but also a capital gain or a capital loss that might come from a number of different sources. The first of these is the roll down return. Which comes from a bond getting closer to maturity and is calculated based on an assumption that the yield curve doesn't change shape over time. on top of that we then have changes in the bond's price arising from expected changes in benchmark yield curves. And further on top of that expected changes in yield spreads contributing to a change in the yield on the bond over time and as a result a change in its price. Of these the least intuitive is probably the roll down return. The roll down return comes from the idea that the yield curve is often upward sloping and as we move forward in time. For yield to maturity declines as that bonds maturity gets closer and the time to maturity Falls so over time we get a decrease in yield as the bonds time to maturity decreases. With lower discount rates we might assume that's going to lead to a higher bond price. But that's not always the case because we also need to take into account the pull to part effect, which described the fact that a bond's price will get closer towards. It's par value as the maturity date arrives. So if a bond is trading at a premium to its par value the pool to power effect may decrease its price even though we might have a lower yield so it's not clear as to what the net effect of the rolling down. The yield cover affect might be on a bond's price. Is worth being aware that this rolling down the yield curve assumes that the yield curve doesn't change over time. Expectations of a change in the yield curve are dealt with through the last two component parts in terms of changes in the yield curve itself from a benchmark yield perspective. So government bonds potentially and then on top of that changes in the yield spread, both of these together can be quantified using duration as a metric of the impact of the expected changes in yields on a bonds price and as a result the return generated for the portfolio.