Then, after the building is actually built and inhabitated, the calculations are adjusted by the actual energy consumption over year).
As pointed out, competent HVAC companies should have people on staff comfortable with such calculations. However, my experience shows that it is not universally true, and many are just guided by intuition/experience with other projects (i.e. the roof insulation thickness on the previous project was X, so that's good enough for you, or "well, on average we recommend 50W/m2 of heating power when selecting a heat source"). Which probably works fine for many cases (e.g. renovating an older building, where even if the material properties when they were new are known, you can only guess the values after 20 years of service).
The most rigorous standard for home efficiency, the Passive House standard, stipulates that no more that 15kWh/m^2/yr is used for space heating. For a 200m^2 house, that's 3000kWh/yr.
Given a 120 day (4 month) heating season, that's 25kWh/day average just for space heating. Obviously it varies quite a bit, with some days much higher and others much lower. Add in other electricity uses, like refrigeration, laundry, and you're easily at 40+ kWh/day even in an efficient Passive House.