I have an excel sheet which looks something like this:

date        text        value        other-value
date        text        value        other-value
date        text        value        other-value
date        text        value        other-value
totals                    sum          other-sum

The sum is of course a sum of all the values above it. What I am wondering is if there is a way I can add rows with a sub-total at random places through out that list. For example if I would like to have a sub-total for each new month. My problem is of course that the total sum will become way to large because it will also sum the rows with the sub-totals. Does Excel have a feature that can help me so I can have the sub-totals and a correct total-total?

I'm using Excel 2010.