The journal impact factor is the average number of citations received in a given year by the articles a journal published in the two preceding years. In plain terms, it estimates how often a typical recent paper in that journal gets cited. Published annually by Clarivate in the Journal Citation Reports, it is the most widely cited, and most widely criticised, journal-level metric in research. Understanding what it does and does not measure is essential for using it sensibly when deciding where to submit.
This guide explains how the impact factor is calculated, its well-documented limitations, and the alternative metrics that give a fuller picture.
How the Impact Factor Is Calculated
The calculation is simple. For a given year, take the number of citations in that year to the journal's articles from the previous two years, and divide by the number of citable articles the journal published in those two years.
For example, if a journal published 200 citable articles across 2023 and 2024, and those articles received 800 citations during 2025, its 2025 impact factor is 800 divided by 200, or 4.0. That single number is then used, often far beyond what it can support, as a proxy for journal quality.
Crucially, the impact factor measures a journal, not an individual article and not an author. A paper in a high-impact journal is not necessarily highly cited itself; conversely, important work appears in modest journals all the time.