What it means
Calculators estimate TDEE by multiplying BMR by an activity factor. Common factors run from about 1.2 for mostly sitting to about 1.9 for very hard daily training or physical work.
Eat close to your TDEE and weight tends to hold steady. Eat below it and you are in a calorie deficit. Eat above it and you are in a surplus.
Any TDEE number is an estimate. People of the same size can differ by a few hundred calories a day, mostly because of everyday movement. Treat the calculator result as a starting point, then adjust based on your actual weight trend over 2 to 4 weeks.
On a GLP-1, appetite often drops so much that intake falls well below TDEE without trying, which is why protein targets matter more.
Why it matters
TDEE is the anchor number for the most-used calculator on Sunny Weigh and for every calorie target.