I don't know much about html, actually i know nothing about web sites, so correct me if i'm wrong - couldn't code which actively tracks and calculates totals for every user add site load, although perhaps small? Maybe add a button to calculate total for month/year/all time on-demand instead of active addition of all trades is a better solution?
Either way, atm the moment it's a huge hassle to calculate total manually, and i think the function suggested here would be an excellent addition to this site.

[x] Yes.