I usually do the math, but I'm getting spoiled by my Alexa (which lives in my sewing room). It's so convenient to just ask Alexa the math questions! Easier than finding my calculator in that room, anyway!
When I used to balance my checkbook by hand I was really good at quickly doing simple arithmetic in my head, but since I've been using online banking for so many years now, I find I have to actually stop and think a bit, even for basic subtraction.