Even if all of those kilograms were pure muscle they would only require 32.5 more Calories per day. Since that isn't very realistic let's assume 50% is fat and 50% is LBM in those calculators: 1.254.5+1.2512.5=21.25 Calories Let's now look at how much energy is required to walk 12.5km with those 2.5 extra kilograms, when the walk is 550-600 kcal: 2.5/80550=17.2 and 2.5/80600=18.75 So my method of adding 2.5 kg results in a 2.5-4 kcal discrepancy whereas not entering the 2.5kg results in a 17-18.75 kcal discrepancy. I think it was quite reasonable to go about it this way.  http://www.bodyrecomposition.com/research-review/dissecting-the-energy-needs-of-the-body-research-review.html/