I submitted a paper to elsevier and it got major revision. I proceeded as per the suggestions and submitted revision. After few days the status changed to "Under Review". Now the status is still under Review even after 45 days. Can I ask the editor for a status update or should I wait further?
Depending on the field, "Under Review" can also be 6 months. The reviewers review in their spare time. If they don't have spare time or are unorganised reviews take very long time.
-By checking the policies of Reed Elsevier, sometimes revision takes 2-4 weeks and the author will be informed directly about the situation whenever it obtained. It depends on several factors such as how many reviewers they have this term and how many submitted papers they have on their system waiting to be evaluated and which field your paper in.
- If you in hurry, there will be no harm if you send a kind email asking about the progress of reviewing your paper.
I think the best advise would be to go to the journal's homepage and browse recently published articles. Each such article has information about when it was (1) received, (2) received in revised form and (3) accepted for publication.
From this, you can easily infer average time that is under revision. Keep also in mind that for many papers there is minor revision so the time interval from (2) -> (3) might be small. You should check towards the higher end of that interval to get some estimation. If you think the time spend under review is unreasonably large, you can send a message to the editor asking about the status. But you should not hurry.