I think a third column in the analytics tab would be great to see how much you have invested as well as spent and earnt. Something simple like a third section would be great and a simple toggle can let people
What about using a category? 
Its more being able to see at a glance how much as a bar / pie chart rather than just a category I do have a category currently but I wouldnt count investing as spending if you see what i mean. Buying into vanguard and eating out arent really the same thing to me and get lumped together id like to split them out
yeah makes sense! Maybe a combined column for invested/ saved ?
Yeah just to separate them as its neither income or real spending
