What is Impact Factor and Does It Matter?
A measured account of how impact factor is calculated, what it indicates, and where its limits lie.
An explanation of the journal impact factor metric, its calculation, its appropriate uses, and the well-documented criticisms of its application to individual researchers and articles.
Frequently Asked Questions
What is a good impact factor?
It depends entirely on the field. In high-volume disciplines like medicine, an impact factor above 5 is strong. In mathematics or specialised humanities subfields, an impact factor above 1 may be excellent. Always compare a journal's impact factor against its subject category quartile (Q1–Q4), not in absolute terms.
How is journal impact factor calculated?
Impact factor for year X = (Citations in year X to articles published in years X-1 and X-2) ÷ (Number of citable articles published in years X-1 and X-2). It is calculated and published annually by Clarivate in the Journal Citation Reports.
Does impact factor matter for tenure and promotion?
It varies by institution and country. Some universities (especially in Asia and Eastern Europe) weight impact factor heavily; others (especially research-intensive UK and US institutions) increasingly de-emphasise it in favour of qualitative assessment, citation counts, and altmetrics. Check your institution's specific tenure criteria.
What are alternatives to impact factor?
Common alternatives include: SJR (SCImago Journal Rank, weighted by citing journal prestige), SNIP (Source Normalised Impact per Paper, normalised by field), CiteScore (Scopus's metric, similar to JIF but uses 4-year window), h-index (combined measure of productivity and citation impact), and altmetrics (social media mentions, news coverage, downloads).
Do all journals have an impact factor?
No. Only journals indexed in the Web of Science Core Collection receive an impact factor from Clarivate. Many legitimate, peer-reviewed journals — especially newer ones, regional journals, and specialised subfield journals — do not have an impact factor. Lack of an impact factor does not indicate low quality.