What Is an Impact Factor?
The impact factor is a metric that estimates how frequently the articles in a scholarly journal are cited by other researchers. It was developed in the 1960s and is published each year in the Journal Citation Reports from a major analytics company. Universities, authors and publishers use it as a rough indicator of a journal's influence, though it is controversial.
How it is calculated
The standard two-year impact factor for a given year is:
Citations in that year to items published in the previous two years, divided by the number of citable items published in those two years.
For example, if a journal published 200 citable articles over 2023 and 2024, and those articles were cited 1,000 times in 2025, its 2025 impact factor is 5.0.
What it does show
- Average attention: how often the journal's recent articles are cited.
- Relative standing: how a journal compares with others in the same field.
What it does not show
- Quality of a single article: a few highly cited papers can raise the average, while most articles may be cited rarely.
- Quality of the research methods.
- Value outside academia, such as influence on practice or policy.
- Comparisons across fields: citation habits differ, so a good impact factor in mathematics may be much lower than in medicine.
- Fairness: the number can be influenced by article types such as reviews, and by self-citation.
Many researchers and organizations have raised concerns about over-reliance on impact factors, and declarations such as DORA encourage evaluating research on its merits.
Other metrics
Alternatives and additions include journal-level measures such as CiteScore and the h-index for journals, and article-level measures such as citation counts and altmetrics, which track mentions in news, social media and policy documents. Each has strengths and limits.
How students can use it
- Do not use impact factor as the only test of a source. Check peer review, the author's credentials, methods and relevance.
- Compare only within a field.
- Be aware that new and specialized journals may have low factors but valuable content.
- Be cautious with fake metrics, since some predatory journals advertise invented impact factors.
- Check the official source for an impact factor claim.
Why it matters
You will meet impact factors in discussions of journals and in some assessment contexts. Understanding what they measure helps you use them wisely.
Related terms
See scholarly journal, peer review, open access, DOI and preprint.
Frequently asked questions
How is the impact factor calculated?
The number of citations in a given year to items the journal published in the previous two years, divided by the number of citable items it published in those two years.
Does a high impact factor mean a better article?
No. It describes the journal's average citations, not the quality of an individual article. Within a journal, citations vary a lot.
Should I use impact factor to choose sources?
It can be one clue about a journal's reach, but judge sources by their methods, relevance and reliability. Compare impact factors only within a field.