Last updated: 29 April 2026 · 7 min read · Audience: Authors, students, early-career researchers · Reading level: Introductory
The journal impact factor is a numerical indicator of the average frequency with which articles published in a given journal during the previous two years have been cited in the most recent year. It is widely cited and widely misused.
How it is calculated
The impact factor for a year Y equals the number of citations recorded in year Y to articles published in the journal during years Y−1 and Y−2, divided by the total number of citable items published by the journal in those two years.
What it can reasonably indicate
- Aggregate citation activity for a journal over a defined window.
- A rough comparative position within a single subject category.
- Trends in journal-level citation behaviour over time.
What it cannot reasonably indicate
- The quality or impact of any individual article in the journal.
- The scholarly contribution of any individual author.
- Comparisons across disciplines with different citation cultures.
- The long-term significance of newly published research.
Alternatives and complements
Article-level metrics, citation counts adjusted for field and time, h-index, altmetrics, and qualitative peer assessment each address aspects that impact factor does not. Responsible evaluation typically combines several indicators with substantive review.
Key points
- Impact factor is a journal-level, not article-level, metric.
- It is most informative when compared within a single discipline.
- It should not be used to evaluate individual researchers.
- A combination of metrics and qualitative review is the responsible standard.
Frequently asked questions
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Editorial enquiries
Questions about this guide or about preparing a manuscript for submission may be directed to the editorial office. Where a query relates to a specific journal in the portfolio, please indicate the journal abbreviation in your message.
Email: editor@ep-journals.org