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 impact factor 2015 for a journal would be calculated as follows:

A = the number of times articles published in 2013-2014 were cited in indexed journals during 2015

B = the number of articles, reviews, proceedings or notes published in 2013-2014

impact factor 2015 = A/B

(note that the impact factor 2013 will be published in 2015, because it could not be calculated until all of the 2014 publications had been received. Impact factor 2015 will be published in 2016)

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:

MIT Biology Hyertextbook
Cell Biology Protocols