About the Journal Impact Factor
The Journal Impact Factor (JIF) is a bibliometric measure of how frequently a journal's recent articles are cited, on average, in a given year. It was introduced by Eugene Garfield and is published annually by Clarivate in the Journal Citation Reports. The standard, two-year Impact Factor is defined as:
Impact Factor = (Citations this year to items published in the prior 2 years) ÷ (Number of citable items published in those same 2 years)
For example, if a journal received 600 citations in the current year to articles it published across the previous two years, and it published 240 citable items across those two years, its Impact Factor is 600 ÷ 240 = 2.5. In plain terms, the average citable article from those two years was cited 2.5 times this year.
What counts in the numerator and denominator
- Numerator (citations): all citations recorded this year that point to articles published in the two prior years, regardless of what document type the citing article is.
- Denominator (citable items): the count of "citable" document types — typically original research articles and substantive reviews — published in those same two prior years. Editorials, letters, and news items are usually excluded from this count.
Because the denominator only counts certain document types while the numerator can include citations from any document type, a journal's classification choices can shift its Impact Factor even if the underlying citation activity does not change.
Self-citations
A journal self-citation occurs when an article in the journal cites another article in that same journal. Self-citations are counted in the official Impact Factor by default, so this calculator also reports the score with journal self-citations subtracted from the numerator, letting you compare the two side by side.
Limitations to keep in mind
The Impact Factor is a field-dependent, average-based metric: citation norms vary enormously between disciplines, a small number of highly cited papers can dominate the average, and a two-year citation window does not suit fields where papers are cited over much longer horizons. Treat it as one input among several — alongside metrics like the 5-year Impact Factor, CiteScore, or article-level citation counts — rather than a stand-alone measure of research quality.