This article describes a measure that can be evaluated for a particular individual person, household, or family. It is not a statistical aggregate, though it may be statistically aggregated to provide average measures and distributions.
The measure may vary with time, i.e., its value may be different at different points in time.
The measure is subjective, as the measurement of its value is based on people's beliefs, opinions, and/or values.
The expected fertility of a female at a given point in time is the completed fertility that the female expects to have by the time her childbearing years are over.
Variation with time
Whereas completed fertility for a given female is a single numerical value determined after completion of childbearing years, and does not change with time, expected fertility can change with time as the female's past trajectory as well as expectations of the future change. For instance, a female who was planning to have only one child may end up conceiving twins and then give birth to them. A female who was planning to have two children may find after having the first child that she does not want, or cannot afford, more.
Gap with desired fertility
Further information: Gap between desired fertility and expected fertility
Expected fertility is closely related to, but different from, desired fertility (also called ideal fertility). The latter refers to the total completed fertility that the female desires. Expected fertility takes into account pessimism about being able to fulfill one's desires. The difference could go either way: it is possible that desired fertility for a given woman is higher than expected fertility. It is also possible that desired fertility for a given woman is lower than expected fertility.
Gap with actual (completed) fertility
Further information: Gap between expected fertility and completed fertility