Definition · Plain-language
Impact factor
The impact factor (Journal Impact Factor, or JIF) is a journal-level metric from Clarivate measuring the average number of recent citations its articles receive — it describes a journal, not an individual paper or author.
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How the impact factor is calculated
The Journal Impact Factor for a given year divides the number of citations recorded that year to a journal’s articles from the previous two years by the number of citable items (research articles and reviews) the journal published over those same two years. So a 2024 impact factor counts 2024 citations to items published in 2022 and 2023. Because it is an average over a two-year window, the metric rewards journals whose articles are cited quickly. Clarivate calculates and publishes it annually in the Journal Citation Reports (JCR), drawing on citation data from the Web of Science Core Collection.
What it does and does not measure
The impact factor is a property of a journal as a whole — it summarises the citation behaviour of a collection of articles, not the quality, rigour or influence of any single paper within it. Citation distributions are highly skewed: a small number of heavily cited articles typically drive most of a journal’s citations, so a typical article in a high-impact-factor journal is cited far less than the average implies. The metric also varies enormously by field, because citation density, publication speed and reference-list length differ across disciplines, making cross-field comparison misleading.
Criticism and responsible use
The impact factor is widely criticised for being skewed by a few highly cited papers, field-dependent, and gameable — through editorial self-citation, excessive review articles or shifting which items count as "citable". Its most serious misuse is judging individual researchers, articles or grant applications by the impact factor of the publishing journal. The San Francisco Declaration on Research Assessment (DORA) and the Leiden Manifesto both call for assessing research on its own merits rather than by journal-level proxies, and many institutions now restrict impact-factor use in hiring and promotion.
Alternatives and complementary metrics
Several journal-level metrics offer different vantage points. CiteScore (Elsevier, from Scopus) uses a four-year window and counts all document types; SCImago Journal Rank (SJR) weights citations by the prestige of the citing journal; Source Normalised Impact per Paper (SNIP) corrects for field citation density to aid cross-discipline comparison; and Eigenfactor scores a journal’s total influence across the citation network. Article-level and author-level measures such as the h-index, citation counts and altmetrics address questions the impact factor cannot, and responsible-assessment frameworks recommend using a basket of indicators alongside expert judgement.
Key facts
At a glance
- Definition: average citations in a year to a journal’s articles from the prior two years
- Level: journal-level metric — describes a journal, not an article or author
- Source: Clarivate Journal Citation Reports (JCR), from Web of Science data
- Window: two-year citation window (a longer 5-year variant also exists)
- Main misuse: judging individual researchers or papers by their journal’s figure
- Alternatives: CiteScore, SJR, SNIP, Eigenfactor, h-index, altmetrics
Common misconceptions
What people often get wrong
Often heard: A high journal impact factor means each article in that journal is highly cited.
Actually: No — citation counts are highly skewed, so a few papers usually account for most citations. The typical article in a high-impact-factor journal is cited far less than the average suggests.
Often heard: You can compare a researcher’s quality by the impact factors of the journals they publish in.
Actually: The impact factor measures a journal, not an individual. DORA and the Leiden Manifesto explicitly advise against using journal-level metrics to assess individual researchers, articles or grant applications.
Often heard: Impact factors are comparable across all fields of research.
Actually: They are not. Citation density, publication speed and reference-list length vary widely by discipline, so a "high" impact factor in one field may be ordinary in another. Field-normalised metrics such as SNIP exist for this reason.
Going deeper
