I was interviewed on last week monday for McKinsey specialist role but have not received any update till now as it’s Tuesday of the next week. Shall I reach out the HR or wait what can be the possible reasons for delay?

First, I'm sorry about this being such a late response but this is how I would generally go about a situation like this: 

Don’t panic. A delay of a little over a week after a final round at McKinsey is not unusual.

Even for specialist roles, decisions often require alignment between multiple interviewers and sometimes a partner review or internal calibration discussion. If one interviewer is traveling or in client meetings, that alone can push feedback by several days. It doesn’t automatically signal a negative outcome.

Since it was your final behavioral round and HR framed it as such, I would suggest the following approach. If you haven’t heard anything after about 7 to 10 business days, it’s completely reasonable to send a short and professional follow-up to HR. Keep it concise. Reiterate your appreciation for the opportunity and ask whether they have an update on the timeline. That shows interest and professionalism, not impatience.

Possible reasons for delay are usually internal logistics, not candidate-related issues. Final-round candidates are typically discussed comparatively, so sometimes firms wait to complete all interviews before releasing decisions.

My advice is to give it a few more days, then follow up once. Stay calm and measured. At this stage, there’s nothing more you can influence except how professionally you handle communication.