Excel sum query - Date of entry

Here is my question; It may be a stupid one, but I can't seem to find the answer to.

Is there a formula in excel that will add up cells depending on when I entered that data into the cell? For example if I entered A123, A124, A125 into cells in one column in January, Then in February I entered another few cells of data in the same column, is there a way to add these up in separate cells for each month?

I hope you get what I mean

Thanks