Quick pre/mid-build question - might help someone wondering the same in future.
If I add 5-10cm to the calculator belt length(s) just to be safe, am I able to adjust to cut any excess off later in the build, or should I cut the length to the exact calculator measurements, which maybe have excess calculated already?
Thanks
If you have got enough belt you can do that and cut it later. 
Great, thanks !
On my LR3 (which should be similar), I built a smaller version first, but cut the belts for the eventual larger (longer and wider) version.
The Y belts had an extra 100 cm (3.3’) or so. I just wrapped up the excess at the YMax location, and it never interfered with anything.
The X belt had an extra 40cm (around 16") or so. I wrapped it at the XMin side of the gantry. It was a bit tricky, I had to route the excess into the gantry behind the struts, otherwise it would interfere when the core traveled to XMin.