Definition of 'Expectations Theory'
The hypothesis that long-term interest rates contain a prediction of future short-term interest rates. Expectations theory postulates that you would earn the same amount of interest by investing in a one-year bond today and rolling that investment into a new one-year bond a year later compared to buying a two-year bond today.
Investopedia explains 'Expectations Theory'
This theory is sometimes used to explain the yield curve but has proven inaccurate in practice as interest rates tend to remain flat when the yield curve is normal. In other words, expectations theory often overstates future short-term interest rates.
Another term-structure theory, preferred habitat theory, expands on expectations theory to explain why longer-term bonds tend to pay more interest than two shorter-term bonds that add up to the same maturity. It says that investors prefer short-term bonds and are only interested in longer-term bonds if they pay a risk premium. While expectations theory assumes that investors only care about yield, preferred habitat theory assumes they care about maturity as well as yield.