Journal Impact Factors

Journal Impact Factor is from Journal Citation Report (JCR), a product of Thomson ISI (Institute for Scientific Information). JCR provides quantitative tools for evaluating journals. The impact factor is one of these; it is a measure of the frequency with which the "average article" in a journal has been cited in a given period of time.

The impact factor for a journal is calculated based on a three-year period, and can be considered to be the average number of times published papers are cited up to two years after publication. For example, the journal impact factor 2018 for a journal would be calculated as follows:

A = the number of times articles published in 2016-2017 were cited in indexed journals during 2018

B = the number of articles, reviews, proceedings or notes published in 2016-2017

impact factor 2018 = A/B

(note that the impact factor 2017 will be published in 2018, because it could not be calculated until all of the 2017 publications had been received. Journal impact factor 2018 will be published in 2019)

Impact factor of Nature, Science and Cell journals can be found on their journal websites.


Science Watch provides ranking and impact factor for selective journals. The list is located here: - PubMed Search Engine
MIT Biology Hyertextbook
Cell Biology Protocols