What is TDEE?
TDEE stands for total daily energy expenditure: the number of calories your body burns in a day. Most of that is your basal metabolic rate — what you would burn lying still in a dark room. Digestion takes a slice. Everything you do on your feet takes the rest, and that includes pacing on the phone and carrying shopping upstairs, not just the hour you spend training.
Eat under the number and you lose weight. Eat over it and you gain. How fast depends on how big the gap is, and that is the whole of it. Knowing your own figure also tells you how much food you have to work with once you start dividing it into protein, fat and carbs.
There is a second reason, and it gets ignored. Eating well under your TDEE for months does not just make you smaller. Recovery gets worse, sessions get harder, and sleep suffers. That usually shows up in the gym weeks before the scale says anything interesting.
How this calculator works
It works out your BMR with the Mifflin-St Jeor equation, published in 1990 in the American Journal of Clinical Nutrition. In that study it predicted resting energy expenditure in healthy adults more closely than the equations in common use at the time, and it is still the default in most clinical practice. Then it multiplies by the activity factor you pick.
BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161TDEE = BMR × activity factorBMR = 370 + (21.6 × lean mass in kg)Activity factors range from 1.2 (sedentary) to 1.9 (professional athlete). If you enter a body fat percentage, the calculator switches to Katch-McArdle, which uses lean mass directly and tends to be closer for people carrying a lot of muscle or very little fat.
Activity factors
Pick the line that matches a normal week for you, not your best week.
| Level | Factor | What it looks like |
|---|---|---|
| Sedentary | 1.2 | Desk job, little walking, no training |
| Lightly active | 1.375 | 1–3 easy sessions a week: walking, yoga, a gentle swim |
| Moderately active | 1.55 | 3–5 real sessions a week: gym work, running, team sport |
| Very active | 1.725 | 6–7 hard sessions a week, or a job on your feet all day |
| Athlete | 1.9 | Two sessions a day, most days |
This is where the estimate usually goes wrong. Three gym sessions and a desk job is 1.375 territory for a lot of people, not 1.55. If you are unsure, take the lower factor. You can always add food later, and adding food is the easier direction to travel.
How to use the number
Treat it as a hypothesis rather than a fact about your body. Eat at your maintenance figure for two or three weeks and weigh yourself a few mornings a week, always under the same conditions. If the average holds steady, the estimate was good. If it drifts, move the target by 100 to 200 calories and give it another fortnight.
For fat loss, 250 to 500 calories a day below maintenance is enough. For muscle gain, 200 to 350 above it puts on less unwanted fat than a bigger surplus. Bigger gaps in either direction mostly buy you a faster number and a worse experience.
Macros
The calorie total decides which way your weight moves. The split decides how bearable the process is, and how much of what you lose is fat rather than muscle. Protein and carbohydrate give you 4 calories per gram and fat gives you 9, so two plates hitting the same calorie target can look nothing alike.
- Moderate carb (30% protein / 35% fat / 35% carb) — the default. Fine for most people and most training.
- Lower carb (40% / 40% / 20%) — more protein and fat. Worth trying if you like fewer, heavier meals.
- Higher carb (30% / 20% / 50%) — more fuel for long sessions and high training volume.
Keep protein at roughly 1.6 g per kg of body weight, which is about 0.7 g per pound, and push it higher while you are cutting. That is the part that protects muscle when calories are low.
Cutting and bulking
Cutting is eating under your TDEE. Bulking is eating over it. The gap sets the pace.
- Cut, −500 kcal/day — around 0.45 kg (1 lb) a week. Hard work, but most people can hold it for a while.
- Mild cut, −250 kcal/day — around 0.23 kg (0.5 lb) a week. Slower, much easier to live with.
- Mild bulk, +250 kcal/day — lean gaining. Very little of it arrives as fat.
- Bulk, +500 kcal/day — faster on the scale, and a bigger share of that is fat.
Give whichever you pick three or four weeks before you judge it. One bad week means nothing. Run the numbers again once your weight has shifted by 5 to 10 kg (10 to 20 lbs), because a lighter body burns less and the old target quietly stops being a deficit. And do not go under 1,200 calories a day without a doctor involved.