If you use a function like NOW()
or TODAY()
in a formula, it will always update to the current time or date. That is the nature of any formula: it evaluates the current situation and returns a result based upon that.
NOW()
will always return the current date and time and TODAY()
will always return the current date. In order to ensure that these functions adjust to the current time, they are volatile, which means that they will re-calculate every time ANY cell in your workbook is changed, whereas non-volatile functions like Sum() will only re-calculate when cells that contribute to their result have changed.
If you want to put a time stamp against a data entry and you do not want that time stamp to change, you either have to enter it manually or use VBA to write the date/time in the next cell.
There are hundreds of sample on the web and on this site. Search for "time stamp" or "date stamp" with Excel as the other keyword. If you get stuck, pipe up.
In case you do not want to go down the VBA track, here are some handy keyboard shortcuts:
Ctrl-; will return the current date
Ctrl-Shift-; will return the current time. You can also think of that as Ctrl-:
If you want to quickly enter a stamp with time AND date into a cell, use
Ctrl-;-space-Ctrl-Shift-;