  The standard methods to calculate the Total Fertility Rate require the
reliable age-specific fertility rate including birth data and the related
age-specific women's population data. Historically, the number of births was
often not counted according to the age of the mother, so it is difficult to
estimate the historical total fertility rate with the standard methods. Many
empirical methods have been proposed, but their application is limited to
specific period and place. This paper deduces a new method for calculating the
total fertility rate from the number of birth and the population of women at
childbearing age, can be applied to most of cases. The relative error is
usually less than 5%. It is easier to calculate TFR, and may be applied to
obtain more TFRs for the history.
