Q: Why is the status of my revised manuscript "Under review" even after 40 days?
I submitted my revised manuscript to the journal after incorporating the reviewer's comments. In fact, I have submitted it on the 21st November 2019. I wanted to know how long it takes for the final decision made by the editor and reviewers. I have heard that reviewers are given 14 days to send their reports to the journal. Is that right? I got major revisions.
You have not mentioned whether you had received a major or minor revisions. The final decision for a manuscript that has received minor revisions might take less time than a manuscript with major revisions. This is because the editor might not send out a manuscript with minor revisions for a re-review. However, a paper with major revisions is almost always sent out for a re-review. If you are lucky, your paper might get accepted after this round, but it's not uncommon for the reviewers to suggest further revisions. Thus, it is difficult to tell how much time the final decision will take after a major revision.
Regarding your question about the deadline assigned to reviewers, this would vary across journals. Some rapid publication journals might give 10-15 days for reviewers to get back with their reports; however, for most journals the review time is longer. Additionally, the holiday season might have caused further delay. Journals usually mention average review times on their website. You can check your journal website to get a clearer idea about this. If you do not see a status change by the end of next week, you can send an inquiry to the journal.