Impact Factor Explained: What It Is, How It Is Calculated, and Whether It Matters

The short answer: Impact Factor (IF) is the average number of citations that articles published in a journal received over the previous two years. A journal with an IF of 4.0 means its papers received an average of 4 citations each in that two-year window. It is published annually by Clarivate in the Journal Citation Reports. It is widely used, widely misused, and widely misunderstood.

How Impact Factor is calculated

The formula is straightforward. Take all citations in year X to papers published in that journal in years X-1 and X-2. Divide by the total number of citable items (articles and reviews) published in X-1 and X-2. The result is the two-year Impact Factor for year X.

Example: a journal published 200 papers in 2023 and 2024. In 2025, those papers were cited 600 times in total. The 2025 Impact Factor is 600 / 200 = 3.0.

A few things worth noting. First, only citations in journals indexed in Web of Science count. Citations from Scopus-only journals, books, conference proceedings, and preprints are not counted. Second, the denominator includes only research articles and review articles, not editorials, letters, or corrections. But the numerator can include citations to those excluded items, which means highly-cited editorials can inflate an IF without raising the denominator. Third, review journals almost always have higher Impact Factors than primary research journals in the same field, because reviews accumulate citations faster and over a longer period.

Impact Factor vs CiteScore: what is the difference?

CiteScore is Scopus's equivalent metric, published by Elsevier. The differences matter in practice.

Because CiteScore uses a four-year window, it is more stable year-to-year and less sensitive to a single highly-cited paper. For slow-citation fields like mathematics or humanities, the four-year window captures a more realistic picture of citation accumulation. For fast-moving fields like clinical medicine or biochemistry, the two-year Impact Factor is more responsive.

A journal can have a CiteScore without having an Impact Factor (if it is indexed in Scopus but not Web of Science). The reverse is also possible, though less common. When comparing journals using these metrics, always compare within the same metric, not across them.

What Impact Factor does not tell you

Impact Factor is a journal-level average. It tells you nothing about any individual paper. A journal with an IF of 6.0 might have 80% of its citations concentrated in its top 5 papers, while most papers receive one or two citations each. Publishing in that journal does not mean your paper will receive 6 citations.

Impact Factor is also heavily field-dependent. Molecular biology and cell biology journals routinely reach IF above 10 because citation rates in those fields are high. A pharmacognosy or natural products journal with an IF of 3.5 may represent exactly the same relative standing within its field. Comparing Impact Factors across disciplines without accounting for field-specific citation norms gives a misleading picture.

The metric is also gameable. Some journals have been caught arranging citation cartels, requiring authors to cite papers from the same journal, or publishing large numbers of review articles (which attract more citations) to inflate their two-year average. Clarivate has suppressed journals from the Journal Citation Reports for such practices.

Finally, Impact Factor does not measure quality. It measures citation rate, which correlates with visibility and reach but not always with methodological rigor or clinical relevance. Some of the most-cited papers in history have later been retracted or substantially questioned.

How journals are ranked within fields: quartiles

Because raw Impact Factor numbers are not comparable across fields, the standard way to assess a journal's relative standing is the quartile system. Within a given subject category, journals are ranked by Impact Factor (in Web of Science) or CiteScore (in Scopus) and divided into four equal groups.

Q1 journals are in the top 25% of their category by the relevant metric. Q2 covers positions 26-50%, Q3 covers 51-75%, and Q4 covers the bottom 25%. A journal can be Q1 in one subject category and Q2 or Q3 in another, depending on how it is classified and which journals it is being ranked against.

For career purposes, Q1 and Q2 publications carry more weight in most evaluation frameworks. Many institutions and funding bodies specify minimum quartile requirements for publications to count toward promotion criteria. Read the guide on Q1 Q2 Q3 Q4 journal rankings explained for a full breakdown of how quartiles are assigned and what they mean in practice.

Impact Factor and open access

Open access publication does not inherently raise or lower a journal's Impact Factor. What matters is whether the journal is indexed in Web of Science and how often its papers are cited. Some high-Impact Factor journals are fully open access. Many open access journals have modest Impact Factors simply because they are newer and have not yet accumulated the citation history that older journals have.

Article Processing Charges (APCs) are separate from Impact Factor. A journal with a high APC does not automatically have a high IF, and paying a high APC does not guarantee good citation performance for your paper. See the guide on open access Scopus journals with low APCs for finding quality open access options without excessive fees.

5-year Impact Factor and other variants

Clarivate also publishes a 5-year Impact Factor, which uses the same formula over a five-year citation window instead of two. This is more appropriate for fields where citations accumulate slowly, such as mathematics, social sciences, or humanities. The 5-year IF is generally higher than the 2-year IF because it captures more of the citation lifecycle of each paper.

The Eigenfactor score is another Web of Science metric that weights citations by the prestige of the citing journal (similar in concept to Google's PageRank). It is less commonly used in practice but available in the Journal Citation Reports. Article Influence Score normalizes the Eigenfactor by journal size to give a per-article measure comparable across journals of different output volumes.

For most practical purposes, researchers choose between the standard 2-year Impact Factor, the 5-year Impact Factor for slow-citation fields, and CiteScore when working with Scopus-indexed journals.

Does Impact Factor actually matter for submission decisions?

It depends on what you are optimizing for. If your institution requires Q1 publications for promotion, then yes, you need to know a journal's quartile, which is related to its Impact Factor relative to its field. If you are an early-career researcher trying to build a publication record, publishing in a lower-IF journal in your field is often more useful than spending a year collecting rejections from journals well above your work's current novelty threshold.

The honest answer is that Impact Factor is one signal among several. Scope fit matters more for whether your paper gets accepted. Peer review quality matters more for whether your paper is actually improved by the process. Indexing status (Scopus, Web of Science) matters for whether your paper gets discovered. Turnaround time matters for your career timeline. The journal selection guide walks through all of these factors in a framework you can apply to your specific situation.

If you know your target discipline and have your abstract ready, the free journal finder tool on this site shows Impact Factor, CiteScore, quartile, APC, and estimated first-decision time for each matched journal, all in one place. No login needed.

Frequently asked questions

What is a good impact factor for a journal?

There is no universal threshold. A good Impact Factor depends on the field. Compare journals within the same subject category rather than against an absolute number. Quartile ranking (Q1 to Q4) is a more useful indicator of relative standing than the raw IF value.

What is the difference between Impact Factor and CiteScore?

Impact Factor is published by Clarivate using Web of Science data over a two-year window. CiteScore is published by Elsevier using Scopus data over a four-year window. CiteScore is free to access and generally higher in absolute value. Both measure citation frequency but are not directly comparable to each other.

Can a journal be Scopus indexed but have no Impact Factor?

Yes. Impact Factor requires Web of Science indexing. A journal can be in Scopus (with a CiteScore) but not in Web of Science (no IF). Many respected journals fall into this category. Check both databases when evaluating a journal's indexing status.

Should I only submit to high impact factor journals?

Not unless your work genuinely meets their novelty and scope requirements. Fit matters more than IF for acceptance rate. A published paper in a relevant Q2 journal reaches your actual audience and counts toward your career, whereas repeated rejections from high-IF journals with the wrong scope do not. Match the journal to your work, not to a number.

Is Impact Factor the same as the h-index?

No. Impact Factor is a journal-level metric. The h-index is an author-level metric. They measure different things and should not be confused. See Scopus vs Web of Science for more on how these databases calculate author and journal metrics differently.