Dynamic table cumulative totals.

I need to figure out how to take prior cumulative totals on a table that will continue to have data added to it. By prior cumulative total I mean, summing all the data except for the last entered row. I made an example sheet with cumulative totals done. I just need to know how to total all but the final row even though you may be adding data.

Thanks

Thank you Ali!

This formula does work for what I need! Just because I am curious and would like to get better at excel, do you think you could explain the "Lookup" part? I understand vlookup, but have never used lookup.