I think most of that is done automatically by computers in the case of airline jets. For single engine aircraft it's mostly DIY. Though with the jets the pilots get many hours of training on what to do if the various systems / computers go wrong.
Believe it or not, weight and balance calculations are not automatic even in the most advanced airliners. The airlines have algorithms they use which spit out numbers that are provided to the pilots, which they enter into the aircraft's computer. These numbers are vitally important, and on one flight I was on we had actually taken the runway but had to taxi back off because Delta was too slow at getting the numbers calculated.
