The impact factor is one of these; it is a measure of the frequency with which the “average article” in a journal has been cited in a particular year or period. The annual JCR impact factor is a ratio between citations and recent citable items published. Thus, the impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years.
The 5-Year Impact Factor. The number of citations in the JCR year ÷ total number of articles published in the 5 previous years = 5-year Journal Impact Factor. The average number of times articles from the journal published in the past 5 years have been cited in the JCR year. 5-Year Journal Impact Factor measurement is the same as the Journal Impact Factor, but with three more years added to both the numerator and the denominator. Instead of a two-year window, it is a five-year window. The calculation is factored in the same manner as the Journal Impact Factor, but considers a five-year window of citation data.