Automatically add extra row to SUM, when added to the first row or last row in section (or summarise until empty cell)

TL;DR: How do I make a summarise-cell, that automatically sums from itself until an empty cell?

I'm working on a budget, looking like this:

It has happened several times, where I've added a new row in the bottom, but forgotten to adjust the =SUM(...)-cell, to include the new row. Like this:

Since when I add the new rows, I like to add them in the top or in the bottom.

How do I get my cell to automatically add newly added row to the sum?