In demography and biology, fertility and fecundity are distinct but related concepts concerning reproduction. Fecundity refers to the biological potential or capacity of an individual or population to reproduce. It is the physiological ability to conceive and produce live offspring. Factors influencing fecundity are primarily biological, such as age, health status, nutritional levels, genetic predispositions, and the presence of reproductive disorders or diseases. For instance, a woman's fecundity peaks in her early twenties and declines with age, while certain medical conditions can impair a person's ability to conceive.

Fertility, on the other hand, refers to the actual reproductive performance of an individual or population, measured by the number of live births. It is the realized outcome of reproductive potential. While fecundity sets the biological limits, fertility is influenced by a wide array of biological, social, cultural, economic, and environmental factors. These include marriage patterns, access to contraception, educational attainment, economic conditions, cultural norms regarding family size, infant mortality rates, and government policies on family planning. A highly fecund individual or population may exhibit low fertility due to conscious choices or external constraints. Understanding both concepts is crucial for analyzing population dynamics, reproductive health, and demographic trends across different human societies.