Belt length - Cut exactly to calculator length or leave margin

I’m sorry if this has already been covered, but I couldn’t find this exact topic. I just want to know if I need to cut the belt with an extra 1"-2" or if that is already factored into the calculator? Very new to this, but anytime I run cable, I always leave a little extra just in case and I wonder if that is bad to do in this case? Does the calculator factor in a little extra? Should there even be a little extra?

Cheers,
Matt

I always cut a little extra. That calculator is set to dead on I am pretty sure. So do a few inches more just to be safe.

Awesome, thanks!