How do governments estimate population totals between census years?

Governments estimate population totals between census years by utilizing vital statistics, provided these records are sufficiently reliable.1

Because a census is an expensive undertaking conducted only at infrequent intervals, demographers use a standard calculation to bridge the gap between enumeration periods. The population for any given postcensal year is estimated using the following formula:1

Population at last census + Births - Deaths ± Net migration = Estimated population1

This method relies on the registration of vital events—such as births, deaths, and marriages—which are typically documented by local authorities. While this approach provides a practical way to track demographic shifts, the accuracy of these estimates depends heavily on the quality and consistency of a country's registry system. Additionally, demographers may use population projections to understand future trends based on assumptions regarding fertility, mortality, and migration rates, which are updated regularly to incorporate new data.23