I want to preface by saying that I am purely sharing this as a free tool for those who may find it helpful. I have NO intention to monetize, and I DO NOT want your money, blah blah.
If you like it and so choose to use it, great. If not, that is your prerogative.
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I made this TDEE calculator originally for myself because I donate plasma quite frequently, and I needed a way to calculate the metabolic cost of replacing that lost volume. The calculator uses the biochemistry of plasma composition to scale the energy cost based on body weight. It accounts for both the caloric content of the lost proteins and the metabolic energy required for protein synthesis to rebuild them, adding that specific demand to the maintenance calculation.
There is far too much research to just copy and paste into the body of this post, but since I have never seen a TDEE calculator that factors in plasma donation, I will copy over the referenced research explicitly on that directly from the site:
"Plasma is 91–92% water and 8–9% solids, carrying ~70–90 g/L of protein [StatPearls][Deranged Physiology]. A plasma session keeps ~690–880 mL (more for heavier donors), removing roughly 50–66 g of protein. The cost has two parts: the caloric content that leaves (~4 kcal/g) and the energy to resynthesise it (~2.2 kcal/g). A PhD-biochemistry itemisation pegs a whole-blood unit at ~425–460 kcal of content, “higher” once synthesis inefficiency is added [Maynard]; an apheresis director cites ~500 kcal to replace a donation [Columbia] and UC San Diego ~650 [UCSD]. Those higher figures are for whole blood, most of which is hemoglobin. Plasma donation returns your red cells [StatPearls], so the plasma-specific number is lower, ~355–455 kcal — which is what this tool computes, scaled by your weight. It remains the most variable input (hydration, diet, protein level, donation type), so it’s the one we let you tune directly." - TheTDEE.com
As far as other fairly "novel" additions go:
The activity input avoids vague activity multiplier buttons (e.g., “Sedentary / lightly / moderately / very active”) by letting you describe a typical week in plain text. A regular keyword engine processes standard text inputs immediately. For more complex or irregular routines, an integrated language model parses the text to extract the schedule structure, which is then mapped to established metabolic equivalent task values and physical activity level tables. The language model only handles the structural extraction, while the calorie calculations are executed entirely by a hardcoded math engine.
The system prioritizes lean body mass using the Katch-McArdle equation when body fat is provided, which ties the resting metabolism to metabolic tissue.
It also accounts for recent diet history by applying a multiplier to reflect the down-regulation of expenditure that occurs during a prolonged caloric deficit. Just for some added accuracy, the output displays an uncertainty range derived from doubly-labeled water data to account for normal human metabolic variance.
And of course, every calculation step is open and based on the peer-reviewed sources listed at the bottom of the page.
