Birth Rate (or Crude Birth Rate) refers to the ratio of the number of births to the average population (or mid-period population) during a certain period of time (usually a year), expressed in ‰. Birth rate refers to annual birth rate. The following formula is used: (Number of births)/(Annual average population)*1000‰. Number of births in the formula refers to live births, i.e. when a baby has breathed or showed any vital phenomena regardless of the length of pregnancy. Annual average population is the average of the number of population at the beginning of the year and that at the end of the year. Sometimes it is substituted by the mid-year population.