Journal Impact Factors (JIFs) are published via Journal Citation Reports (JCR). JIFs, which are calculated from data indexed in the Web of Science Core Collection, are a measure of the frequency with which the "average article" in a journal has been cited in a particular year, helping to evaluate a journal's relative importance, especially compared to others in the same field. The JIF is calculated by dividing the number of current citations from an article published in the two previous years, by the total number of articles published in the two previous years.

However, JCR notes that JIFs "...should be used with careful attention to the many factors that influence citation rates, such as the volume of publication and citation characteristics of the subject area and type of journal. The Journal Impact Factor can complement expert opinion and informed peer review. In the case of academic evaluation for tenure, it is inappropriate to use a journal-level metric as a proxy measure for individual researchers, institutions, or articles."