When do you consider last day of period?

I was wondering when you should consider your last day of period on this app. I mean I usually stop after 6/7 days however this cycle I’ve had a little brown spotting (old blood).

So is this considered an 8th day for a period or is it just left overs from yesterday that didn’t flush out as quick?!

Honestly confused and have been for a very long while!

When is it your last day for a period?! When you see no blood at all or it can be your last day and still have left over old blood?