Impact Factor Calculator (2-year Journal Impact Factor, JIF)

Understanding the journal impact factor calculator — concept and principle

This calculator works out a journal's two-year impact factor from citation and article counts, following Clarivate's definition, and breaks the result down by year. Researchers, librarians and editors use it to understand how the figure is built or to estimate it from their own counts.

Citations per citable item: with the default inputs the result is JIF 4.655 (2,700 ÷ 580).

How it is calculated

JIF for year Y = (C(Y−1) + C(Y−2)) ÷ (N(Y−1) + N(Y−2))

C = citations made in year Y to anything the journal published in that earlier year.
N = citable items (documents typed Article or Review) published in that year.
Citations per item for each year = C ÷ N.
Extra citations needed to raise the JIF by 1.0 = N(Y−1) + N(Y−2).

The principle

The impact factor is an average: citations received in one year divided by the number of recent papers that could have attracted them. Using a two-year window captures the period when many papers in fast-moving fields are cited most. An asymmetry matters: the numerator counts citations to everything the journal published, including editorials and letters, while the denominator counts only articles and reviews. Journals that publish many front-matter items can therefore score higher. Because it is a mean, a few highly cited papers can lift the figure a lot.

Worked example

Default inputs: 1,200 citations to last year's items, 1,500 to items from two years ago, 300 and 280 citable items.

Citations counted = 1,200 + 1,500 = 2,700.
Citable items = 300 + 280 = 580.
JIF = 2,700 ÷ 580 = 4.655.
Per item: last year 1,200 ÷ 300 = 4; two years before 1,500 ÷ 280 = 5.36.
Raising the JIF by 1.0 needs 580 more citations.

Each point is the calculator re-run with only “Citable items (articles + reviews) published last year” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Citable items (articles + reviews) published last year	Journal Impact Factor
75	7.606
150	6.279
225	5.347
300	4.655
375	4.122
450	3.699
600	3.068

How to read the result

Impact factors differ greatly between fields, because citation habits differ; compare journals only within the same field. The figure describes a journal, not an individual paper or researcher, and most papers in a journal receive fewer citations than the mean. Official values come from Journal Citation Reports; counts from other databases usually give a different number.

Common mistakes

Counting all documents, not just articles and reviews, in the denominator.
Using citations from several years instead of one year.
Comparing impact factors across different disciplines.
Judging a single article by its journal's impact factor.

Keep in mind: This calculator reproduces the formula only. Use the official Journal Citation Reports value for any formal purpose.

Frequently asked questions

How is the journal impact factor calculated?

Citations in one year to items from the previous two years, divided by the citable items published in those two years.

What counts as a citable item?

Documents classed as Article or Review in Web of Science.

Is a higher impact factor always better?

It reflects average citation in a field; it says little about any single paper.

Sources: Clarivate, InCites Indicators Handbook, "Journal Impact Factor (JIF)"

Checked 9 Nov 2026. Clarivate, InCites Indicators Handbook, “Journal Impact Factor (JIF)”: numerator = citations in the JCR year to items published in the two previous years; denominator = citable items (Article or Review) published in those two years.

Your numbers