At the beginning Vs In the beginning

I had a student ask me the other day about the difference between using “at the beginning” and “in the beginning” when talking about dates.

I told them there’s basically no difference—both can be used.

Later on, I gave it some more thought, and after checking around, I think there might be some nuance worth pointing out.

For example, take these two sentences:

At the beginning of 2008, our company was founded by John Jones.
In the beginning, our company was run by John Jones.

One is talking about a specific time frame, and the other is a more vague reflection of something that happened early in the company’s history.

So if I were to give any advice:
When a date is involved use “at.”
When you’re being more general use “in.”