I built a TDEE calculator, and you can try it for free at tdee.nathaliemaes.be. I’m studying to become a personal trainer, and I wanted to put what I’ve learned so far into something real. The calculator is built on my lessons about metabolism, and building it was a good way to learn them: every part forces me to understand why the number is what it is.
What is TDEE?
TDEE stands for Total Daily Energy Expenditure: the number of calories your body uses in a day. It adds up several parts:
- Resting energy. What your body burns just to keep you alive, even if you lie in bed all day.
- Everyday movement. Walking, standing, chores and everything else that isn’t a workout.
- Training. The calories you burn when you exercise.
- Digestion. Your body also uses energy to process the food you eat.
Knowing your TDEE gives you a starting point for a calorie target, whether you want to lose fat, maintain your weight or build muscle.
What the calculator does
The calculator asks eight short questions: your age, weight, body fat, daily activity, diet, training and goal. If you don’t know your body fat, you pick the picture that looks most like you.
You get back:
- A target for training days and one for rest days. Training burns extra energy, so a single flat number hides that difference.
- A weekly average that matches how often you actually train.
- A suggested pace, with the reasoning behind it and what to expect each week. A slider lets you choose a gentler or bolder pace.
It’s free, there are no accounts, and your answers stay on your device. The results are estimates, not promises.
What I put into it from my course
The calculator puts my lessons about metabolism into practice. Every step of the calculation is something I had to understand before I could build it. This is how the pieces fit together.
| Step | What the calculator does |
|---|---|
| Resting energy | Uses the Katch-McArdle equation: 370 + 21.6 × fat-free mass (kg). Because it uses body fat, two people with the same weight can get different results. |
| Everyday movement | Multiplies resting energy by an activity factor of 1.40, 1.55, 1.75 or 1.90, based on FAO/WHO/UNU guidance. Training is not included here. If you’re unsure, the calculator tells you to pick the lower option, because people tend to overestimate their activity. |
| Digestion | Adds the energy your body uses to process food: 7%, 10% or 14% depending on your diet. Whole, protein-rich food costs more energy than processed food. |
| Training | Adds the extra energy of a lifting session, using a MET value of 4.5. You can enter your sessions as active minutes or as sets. |
| Pace | Sets a deficit or surplus based on your body fat or training experience. The pace is cautious on purpose, to protect muscle. |
| Safety floors | Shows a warning instead of a number if the target falls below 1,200 kcal for women, 1,500 kcal for men or 80% of resting energy. |
The full list of formulas and sources is on the How it works page.
What’s next: the calculator doesn’t give macros yet. Once I’ve learned the sections on protein, carbohydrates and fats, I’ll add detailed macros.
How it’s built
The calculator is written in React. It’s also a PWA, a progressive web app, which means it works like a normal website but you can add it to your phone’s home screen and open it like an app.
The calculations run in your browser, so your answers never leave your device. That matters here, because the questions are personal: weight, body fat and goals.
Try it
You can work out your own target in a few questions. If your weight doesn’t change, eat to the number consistently for two to three weeks, then adjust based on your scale and measurements. Questions? The FAQ answers the most common ones.
The calculator gives general estimates for healthy adults. It’s not medical advice. Please talk to a doctor or registered dietitian before making big changes to how you eat.