The ZIP archive attached to this publication contains the following files: MNoB-PESEL.csv CSV file containing monthly birth numbers in the years 1899-2010 calculated on the basis of birth dates of Polish citizens registered in the General Electronic System for Registration of the Population (PESEL). MNoB1932-SP.csv CSV file containing monthly number of births in 1932 calculated on the basis of daily numbers of live wedding births in 1932, in Poland excluding capital city of Warsaw (Zaremba 1936) YNoB-SP.csv CSV file containing annual numbers of live births in the years 1900-2009 obtained from Statistics Poland, Szulc 1936, and Jelonek 1986 Code.Rmd R Markdown document containing the code of all calculations made. These calculations were applied by means of programming language R, version 3.4.2 and integrated development environment RStudio, version 1.1.447. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see . Code.html HTML document containing the code in R language of all performed calculations and the obtained results.