Why an online TDEE calculator is only a guess
A TDEE calculator gives you a clean number, but it is built on two guesses about your body. Two weeks of honest logging in Burnie turns that guess into your real number.
You open a TDEE calculator online. You type your age, weight, height, and sex. It gives you a neat number, like 2,200 kcal a day. It looks exact. It feels like a lab verdict. But it is only a clever guess. The guess can be off by hundreds of calories. This short read shows why, and how to fix it in two weeks.
The TDEE number from an online calculator is exactly what you burn each day.
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A calculator does two guesses, one on top of the other. First it guesses your resting burn from a formula. Then it multiplies that by an activity number you choose yourself. Stack two guesses, and the blur grows. Even the best formula lands within 10 percent for most people. Some are further off. You will not know which one you are.
What 'within 10 percent' really means
Ten percent sounds small. On a 2,000 kcal day, it is about 200 kcal. That is like two extra rotis, every single day. A big review looked at BMR formulas. The best one, Mifflin-St Jeor, still only nailed most people within 10 percent. It also warned of "noteworthy errors" for individuals. A second paper put it plainly. Even the best tools carry over 100 kcal a day of blur. A 100 to 200 kcal blur is big. It shifts your predicted weight by about 2 to 4 kg in a year.
Three ways to find your number
How to turn the guess into your number in two weeks
The bottom line
A TDEE calculator is a great starting point. It is not a verdict. The formula alone can miss by about 200 kcal on a 2,000 kcal day. Even the best lab tools carry over 100 kcal of blur. So use the number, then check it on your own body. Two weeks of honest food logs and daily weights turn a clever guess into YOUR number. That is when the maths starts working for you.