Journal citation reports (JCR) (click ‘Full text availability’/’Kokotekstin saatavuus’ to access the database) is the only official source for impact factor (IF) values, produced by Clarivate Analytics. JCR contains impact factor values and other indicators of all journals included in the Web of Science database. Clarivate Analytics owns the impact factor values, and no other party is allowed to publish them at least carrying the same title. JCR can be used as a part of the Web of Science database.
Guidance for finding a journal’s impact factor in the JCR database (see: IF (Impact Factor) -> How to find an Impact Factor number).
Clarivate Analytics. 2017. Journal Citation Reports: Learn the Basics.
Web of Science Training. 2017. Video (5:16): Journal Citation Reports – Journal Impact Factor.