The crude birth rate (CBR) is the total number of live human births per 1,000 population for a given period divided by the length of the period in years. It is a measure of the fertility of a population and is generally computed as a ratio. The CBR is distinguished from a set of age-specific rates, which is the number of births per 1,000 persons, or more usually 1,000 females, in each age group. When the crude death rate is subtracted from the crude birth rate, the result is the rate of natural increase (RNI), which is equal to the rate of population change (excluding migration).

The crude birth rate is an important indicator for public health assessment and is based on data from birth and death registration systems, censuses, and sample surveys by national statistical offices and other organizations, or on demographic analysis. Vital registers are the preferred source for these data, but in many developing countries, systems for registering births and deaths are absent or incomplete because of deficiencies in the coverage of events or geographic areas. Many developing countries carry out special household surveys that ask respondents about recent births and deaths, and estimates derived in this way are subject to sampling errors and recall errors.