Journal Impact Factor

Journal Impact Factor

What is Impact Factor ?

The impact factor is an index (numerical value) to evaluate how much impact a journal (scientific journals) has. It is one of method for compare journals in the same field.
Impact factors are calculated each year based on the citation status of the articles from a database "Web of Science" by Clarivate Analytics published in the journal in the past two years.

Calculation method

The calculation method for an impact factor for a target year is as follows:

Total cited count of articles published in the journal for the last two years in the target year
/ The number of articles published in the journal for the last two years before the target year

For example, the 2018 impact factor can be calculated as follows:

Calculation  of a impact factor in 2018


Let's say 305 papers are published on journal in 2016 and as well 315 papers in 2017, and these 620 (=305+315) articles are cited 1519 times in 2018.
In that case, an impact factor on the journal is calculated by
(cited count in 2018 for articles in 2016 + cited count in 2018 for articles in 2017)
/ (the number of articles in 2016 + the number of articles in 2017)

Other indexes

In addition to the impact factor, several metrics are available in the Journal Citation Reports.

  • 5-Year Impact Factor
  • This is a variation of the impact factor based on citation data for the last five years, instead of two years for the original impact factor.
    It is suitable for journals with a long period from publication to citation.

  • Immediacy Index (Reference:"Immediacy Index" in InCites help)
  • This is an index that is calculated as the average cited count during a year for the entire article published within the year.
    It is useful for comparison of rapidly‐advancing field journals.

  • Eigenfactor Score (Reference: About the Eigenfactor® Project

    This is advanced index for cover the disadvantage of impact factor that the value depends on the scale of the journal.

Things to be careful of :

(Reference page:"The Clarivate Analytics Impact Factor"

☆The impact factor cannot be used for comparison between different fields

Determining the impact factor involves various factors such as the researcher population in each field, citation trends in papers, and citations from other fields. For this reason, it is difficult to compare different fields because the impact factor depends on various factors such as the researcher population in each field, citation trends in papers, citations from other fields etc., and the average citation number of a field or the relationship between the number of years since publication and the citation number is different for each field.
In such case, instead of the impact factor, try another methods such as comparing the number of citations and citations in leading journal in their own field.

☆The impact factor is not an index for the evaluation of papers or researchers

The impact factor does not always represent appropriately the cited status of each paper.
The committee jointly established by the International Association of Mathematical Sciences (IMU), the International Council of Applied Mathematics (ICIAM), and the Institute of Mathematical Statistics (IMS) described risks of the impact factor in a report, “IMU-ICIAM-IMS Report Citation Statistics” (PDF link:
Another research analysis tool "InCites" is useful for evaluating individual papers and researchers. (Reference: InCite introduction page)

☆Be careful when using the impact factor for small-scale academic journals

In case of small-scale journals, an impact factor value may change more drastically by chance than large-scale ones because of the calculation method.
For such journals, you should also check impact factors for the past few years.

☆The impact factor cannot express properties other than number of citations

The impact factor is a measure based on the number of citations, thus it does not represent other properties such as the tendency of articles published in the past, the detailed fields of journals and what kind of journals cite the papers on the journal.

Check impact factors with the Journal Citation Reports

How to check ?

Impact factors are listed on the database "Journal Citation Reports (JCR)". JCR can be accessed from within the Hokkaido University because it is a database contracted at the university. If you are using from off campus, please use remote access service.

Jounal Citation Reportsのトップ画面

Journal Citation Reports provides various function to check an impact factor and compare impact factors. (Also refer to the Journal Citation Reports training page)

List of journals

Journal Citation Reportsのスクリーンショット

By clicking the "Browse Journal" button on top page, title of journals and their impact factors are listed.
The list can be order by the value of impact factor and total cited count and narrowed down by title and field.

Journal Citation Reportsのフィルター機能のスクリーンショット
The list can be filtered by category, publishers, open access status, and others.

The following topics are descriptions of the features that were available in Journal Citation Reports(Classic), the former version of the interface.

Some of the features are noted as "COMING SOON" in the new interface as of 2021/08/11.
The classic version of the interface will be accessible until the end of 2021(cf. Clarivate Releases Journal Citation Reports, Naming the World’s Leading Journals).

Compare journals

Journal Citation Reportsのスクリーンショット

By selecting "Compare Journals" on top page and then choose the "Compare Journals" on the left side, you can compare values of impact factors of multiple journals.

See the detail of journal information

Journal Citation Reportsのスクリーンショット

By clicking on the journal name in the "Browse by Journal" list, you can check the following details of each journal:

  • Transition of impact factor in the past 5 years
  • Distribution of cited counts for published articles for each year
  • List of journals which have cited the journal
  • Top 10 institutions the authors of the journal belong

See a list of the research fields

Journal Citation Reports

By selecting "Browse by Category" on the top page, you can check the statistics of impact factors for each field (such as the average or median impact factor in the field).
You can also see the list of journals in the field by clicking the numbers in the "#Journals" column.
specify the related field from journal title (left column: Search by the journal title from Select Journals).


User Guide for Clarivate Analytics Products

About Impact Factor (Clarivate Analytics)

A movie guide to JCR's new interface and features on a learning portal of Clarivate Analytics

【Contact】 University Library Research Support Division (jsa [at]