In the Iurnin Citation Reports (JCR) is calculated by dividing the number of citations for the current year of articles published in the previous two years by the total number of articles published in those two years. It is calculated annually in two editions, Science and Social Sciences Edition.
Examples: to determine the impact factor of a magazine during the year 2007:

Thus, if a magazine has been quoted once, on average, for each published article it is necessary to understand that the impact factor will be 1. To find out if an impact factor is high or not, you must compare it with the impact factor of other magazines in the same Subject Category.