How this instrument works
The Journal Impact Factor (IF) is the metric Clarivate publishes each year in the Journal Citation Reports (JCR) to summarize how often a journal's recent articles get cited. It is a simple ratio: the number of citations that arrived during the JCR year to anything the journal published in the two years before it, divided by the number of citable items — articles and reviews — the journal published across those same two years.
The numerator and denominator do not count the same things, which trips up a lot of first-time readers. The denominator only counts 'citable items,' meaning research articles and review articles — it excludes editorials, letters, and news pieces. The numerator, by contrast, counts citations to anything the journal published in that window, including those non-citable items. That asymmetry means a journal's IF can shift based on how its content is classified, not just how often it is cited.
Because citation habits differ enormously by field — a molecular biology paper accumulates references far faster than a pure mathematics paper — Impact Factor is only a fair comparison within the same discipline, and even then only a rough one. Clarivate itself recommends reading a journal's percentile rank within its JCR subject category rather than treating the raw Impact Factor as a universal yardstick across fields.
- Enter Citations in year — the total citations the JCR year recorded to items the journal published in the prior two years.
- Enter Citable items — the count of articles and reviews, not editorials or letters, the journal published across those same two years.
- Read Journal Impact Factor — the citations-per-citable-item ratio the instrument computes instantly.
- Compare journals only within the same JCR subject category — citation norms vary too much across fields for the raw number alone to mean much elsewhere.
Worked example — 450 citations, 150 citable items
Enter 450 into Citations in year and 150 into Citable items — a mid-sized specialty journal that published 150 citable articles and reviews across the prior two years and drew 450 citations to that body of work during the JCR year. Journal Impact Factor reads 450 / 150 = 3.0.
An IF of 3.0 means that, on average, each citable item the journal published in those two years was cited three times during the JCR year. That average hides a lot of variance — a handful of highly cited papers usually pull the number up while most articles are cited less often or not at all — which is why Impact Factor describes a journal's citation profile, not any individual article's quality.
Questions
What counts as a 'citable item' for the Impact Factor denominator?
Clarivate classifies only research articles and review articles as citable items. Editorials, letters, news pieces, corrections, and meeting abstracts are excluded from the denominator even though they can still attract citations that count toward the numerator. This split is the single most misunderstood part of the calculation.
Why do the numerator and denominator cover different content?
The numerator counts citations to everything the journal published in the two-year window, including non-citable items like editorials, because those items can genuinely be cited. The denominator restricts itself to articles and reviews on the theory that those are the items readers expect to generate citations. The mismatch is a known, debated feature of the JCR methodology, not a calculation error.
Can I compare Impact Factors across different research fields?
Not reliably. Fields with fast-moving literatures and large reference lists, like cell biology, naturally produce higher Impact Factors than fields like mathematics or classics, where papers accumulate citations more slowly over a longer horizon. Clarivate's own guidance is to compare journals within the same JCR subject category, or to use the category-normalized percentile rank instead of the raw IF.
Does a high Impact Factor mean every article in that journal is high quality?
No. Impact Factor is a journal-level average, and citation counts within any journal are typically skewed — a small number of highly cited papers pull the average up while most articles are cited far less. A high IF says the journal's output was cited often on average during the window measured; it says nothing about any single article you're evaluating.
Who calculates the official Journal Impact Factor?
Clarivate calculates and publishes it annually in the Journal Citation Reports, drawing on the Web of Science citation database. Only journals indexed in Web of Science Core Collection receive an official Impact Factor, which is why some respected journals in smaller fields don't have one at all.
Will this calculator match the exact number Clarivate publishes?
It will match Clarivate's number for the same two inputs, because it uses the identical citations-divided-by-citable-items formula. What this tool cannot do is source or verify the citation and citable-item counts themselves — those come from Clarivate's own indexing of Web of Science data, which you would need to pull from a current JCR report.