TDEE Calculator: How AI Food Coach Calculates Your Daily Calories
Most calorie calculators give you a static number. Enter your weight, height, age, pick an activity level from a dropdown, and you get a number that never changes. That's not how your body works.
AI Food Coach calculates your TDEE dynamically — it updates as you eat, move, and log weight. Here's exactly how it works, with the actual formulas from the app's source code.
What is TDEE?
TDEE (Total Daily Energy Expenditure) is the total number of calories your body burns in a day. It has three components:
- BMR (Basal Metabolic Rate) — calories burned at rest, just to keep you alive. About 60–70% of the day's burn for a sedentary or lightly active person (FAO/WHO/UNU 2004).
- Activity — calories burned through movement, exercise, and daily activities. Most of the rest.
- TEF (Thermic Effect of Food) — calories burned digesting food. About 10% on a mixed diet, more with more protein (Westerterp 2004).
AI Food Coach shows all three — and updates them throughout the day.
Step 1: BMR — Your Base Metabolic Rate
BMR is the energy your body needs at complete rest — lying in bed, not moving, not digesting food. It's the largest component of your daily burn.
AI Food Coach uses two published formulas and picks one automatically:
Mifflin-St Jeor (Default)
The default formula. Used when body fat percentage is not set.
Women: BMR = (10 × weight_kg) + (6.25 × height_cm) - (5 × age) - 161
Example: A 30-year-old man, 80 kg, 180 cm:
BMR = (10 × 80) + (6.25 × 180) - (5 × 30) + 5 = 800 + 1125 - 150 + 5 = 1,780 kcal
Why Mifflin-St Jeor?
Mifflin and St Jeor derived it in 1990 from 498 healthy adults aged 19–78 whose resting energy was measured by indirect calorimetry. In the same people, the 1919 Harris-Benedict equations overestimated it by 5% (Mifflin 1990).
Katch-McArdle (When Body Fat % is Known)
A formula that uses lean body mass instead of total weight (Cunningham 1991). Used automatically when you set your body fat percentage.
BMR = 370 + (21.6 × LBM)
Example: Same 80 kg man, 20% body fat:
LBM = 80 × (1 - 0.20) = 64 kg
BMR = 370 + (21.6 × 64) = 370 + 1382 = 1,752 kcal
Why it matters: Two people can weigh 80 kg but have very different body compositions. One has 15% body fat (68 kg lean mass), another has 30% (56 kg lean mass). Mifflin-St Jeor gives them the same BMR. Katch-McArdle gives the leaner person a higher BMR — resting energy depends mostly on lean mass (Cunningham 1991).
Auto-selection: You don't need to choose a formula. Set your body fat percentage in the app → Katch-McArdle activates automatically. Don't know your body fat? Mifflin-St Jeor works well as default. The Calorie Calculation screen shows which formula is active.
Apple Watch Instead of the Formula
If you wear an Apple Watch or another tracker that writes resting energy to Apple Health (Health Connect on Android), the app uses that number instead of both formulas. It is an estimate too — Apple says the watch uses your height, weight, sex and age, among other things, to calculate the calories you burn — so the app checks it first: a value below 70% of your formula BMR is ignored, and it counts only together with active energy.
The app reads yesterday's resting energy for stability (today's data is incomplete until midnight). It also keeps a 30-day average to correct days with incomplete data — for example, if you forgot to charge your watch or didn't wear it all day.
Step 2: Activity — Three Tiers of Accuracy
Activity calories are the hardest part to estimate. A category like “Moderate” gives the same number every day — your days are not the same.
AI Food Coach supports three tiers, from least to most accurate:
Tier 1: No Wearable (Activity Multiplier)
The classic approach. Your BMR is multiplied by an activity factor:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little exercise |
| Light | 1.375 | 1–2 workouts a week |
| Moderate | 1.55 | 3–5 workouts a week |
| Active | 1.725 | 6–7 workouts a week |
| Very Active | 1.9 | Athlete, physical job |
Problem: the multiplier is the same every day, while your days are not. With Apple Health on, the app takes your level from the workouts it records; without it, an activity you log replaces the multiplier for that day.
Tier 2: iPhone Only (Formula BMR + Active Energy)
With HealthKit enabled but no Apple Watch, the app uses:
The iPhone estimates active energy from your steps and movement, so it follows your day instead of a fixed multiplier. BMR still comes from the formula: the app ignores a resting-energy value below 70% of it. On Android, Health Connect works the same way with the active energy your phone or tracker records — or, from a watch that writes only its total calories (such as Pixel Watch), the active part of them.
Tier 3: Apple Watch (Resting + Active Energy)
Both parts come from the watch:
No multiplier is needed: the watch's numbers follow your day. They are estimates — in a lab study of seven wrist devices none estimated energy expenditure within 20%, and Apple Watch came closest (Shcherbina 2017).
On Android, a watch or tracker that writes both resting and active energy to Health Connect works the same way.
Why yesterday's basal?
Today's basal energy reading is incomplete until midnight — it grows throughout the day. Using yesterday's completed measurement gives a stable, accurate value. The app also maintains a 30-day average to smooth out days with incomplete data — e.g., if you forgot to charge your watch or didn't wear it on your wrist all day.
Step 3: TEF — The Hidden Calorie Burn
Digesting food burns calories too — and the amount depends on what you eat.
TEF (Thermic Effect of Food) is the energy cost of digesting, absorbing, and processing the food you eat. Different macronutrients have very different thermic effects:
| Macronutrient | Thermic Effect | Example (100g) | TEF Calories |
|---|---|---|---|
| Protein | 25% | 100g × 4 kcal × 0.25 | 100 kcal |
| Carbs | 7.5% | 100g × 4 kcal × 0.075 | 30 kcal |
| Fat | 2.5% | 100g × 9 kcal × 0.025 | 22.5 kcal |
The formula used in the app:
Example: You eat 150g protein, 30g carbs, 120g fat in a day:
TEF = (150 × 4 × 0.25) + (30 × 4 × 0.075) + (120 × 9 × 0.025)
TEF = 150 + 9 + 27 = 186 kcal
That's 186 calories burned just by digesting your food. With these coefficients, a high-protein keto day comes to about 100–200 kcal.
TEF is dynamic. Your calorie target grows as you eat throughout the day. In the morning (0 meals logged), TEF = 0 and your target equals the base value. After a high-protein lunch, the target increases because your body will burn more calories digesting it. This is reflected in real-time on the dashboard.
Why Add It?
The resting and active energy from your watch or Health do not include TEF, so the app adds it. Without Health data it adds TEF to BMR × activity multiplier as well: the usual multipliers are lower than the physical activity levels measured in the FAO/WHO/UNU energy report (total ÷ basal energy expenditure — 1.40–1.69 for a sedentary or lightly active lifestyle), and Sedentary 1.2 plus TEF comes to about 1.3.
References: Hall (2010) — thermic coefficients for macronutrients. Westerterp (2004) — diet-induced thermogenesis review.
Your Calorie Target
Once TDEE is calculated, the app determines your daily calorie target:
How Deficit is Calculated
Your weekly weight loss goal determines the daily deficit:
7,700 kcal is the approximate energy content of 1 kg of body fat. So:
- 0.25 kg/week → 275 kcal/day deficit (gentle)
- 0.5 kg/week → 550 kcal/day deficit (moderate)
- 0.75 kg/week → 825 kcal/day deficit (aggressive)
- 1.0 kg/week → 1,100 kcal/day deficit (maximum)
The app enforces safety minimums — it won't suggest a target below 1,200 kcal for women or 1,500 kcal for men, regardless of how aggressive the deficit is.
Dynamic Deficit — Why the Scale is the Only Source of Truth
Everything above — the BMR formulas, the smartwatch data, the TEF calculation — is our best effort to estimate how many calories you burn. And it's pretty good. But it will never be perfect.
The bigger source of error isn't your TDEE — it's the food side. You estimate 150g of rice but it was 180g. You forget to log a handful of almonds. The nutrition label rounds down. These small inaccuracies add up over weeks.
That's why AI Food Coach doesn't rely solely on the math. The scale is the only source of truth.
How It Works
When you set a weight goal, you enter your current weight, your target weight and a timeline in weeks. The app shows the weekly pace (at most 1 kg a week) and your target date.
With Dynamic Deficit on (the default), the app recalculates every day and after every weigh-in:
The remaining kilograms come from your 7-day average weight, so a single high or low weigh-in does not swing it. That new rate determines your daily calorie deficit. If you're ahead of schedule, the deficit shrinks. If you're behind, it increases. The target date stays fixed — the deficit adjusts to get you there.
Example
Say your goal is to go from 85 kg to 80 kg in 10 weeks (0.5 kg/week):
| Week | Weigh-in | Remaining | Weeks left | New rate | What happens |
|---|---|---|---|---|---|
| 0 | 85.0 kg | 5.0 kg | 10 | 0.50 kg/wk | Starting plan |
| 2 | 84.5 kg | 4.5 kg | 8 | 0.56 kg/wk | Behind schedule → deficit increases slightly |
| 4 | 82.8 kg | 2.8 kg | 6 | 0.47 kg/wk | Ahead of schedule → deficit decreases, you eat more |
| 8 | 80.5 kg | 0.5 kg | 2 | 0.25 kg/wk | Almost there → gentle coast to finish |
| 9 | 80.0 kg | 0 kg | 1 | — | Goal reached → the app offers a new goal |
Notice how the system self-corrects. Week 2 was slower than planned — maybe you underestimated portions or had a social dinner. The deficit nudged up. By week 4 the faster loss brought you ahead, so the deficit eased off. You never had to manually adjust anything.
Safety Limits
The dynamic deficit has built-in guardrails:
- Maximum 1 kg/week — even if you're far behind schedule, the app won't suggest a dangerously aggressive deficit
- Minimum 1,200 kcal a day for women, 1,500 for men — your calorie target never drops below it, regardless of the calculated deficit
- Goal reached — when you hit your target weight, the app congratulates you and offers to set a new goal; Stay Healthy holds your new weight. Until you choose one, it keeps the pace you set.
This is how you reach your goal despite daily inaccuracies. No calorie tracker is perfectly accurate — not this one, not any other. The difference is what happens next. A static deficit ignores reality and hopes the math works out. A dynamic deficit checks your actual progress on the scale and course-corrects every time you weigh in.
Frequently Asked Questions
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2):241-247. AJCN
- Cunningham JJ. (1991). Body composition as a determinant of energy expenditure: a synthetic review and a proposed general prediction equation. American Journal of Clinical Nutrition, 54(6):963-969. AJCN
- FAO/WHO/UNU. (2004). Human energy requirements: report of a joint FAO/WHO/UNU Expert Consultation. FAO Food and Nutrition Technical Report Series 1. FAO
- Westerterp KR. (2004). Diet induced thermogenesis. Nutrition & Metabolism, 1(1):5. PMC
- Hall KD. (2010). Predicting metabolic adaptation, body weight change, and energy intake in humans. American Journal of Physiology – Endocrinology and Metabolism, 298(3):E449-E466. PMC
- Shcherbina A, Mattsson CM, Waggott D, et al. (2017). Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. Journal of Personalized Medicine, 7(2):3. PMC
- Apple. Get the most accurate measurements using your Apple Watch. Apple Support
See Your Real TDEE
Download AI Food Coach, set up your profile, and see your dynamic TDEE with all three components — BMR, Activity, and TEF — calculated in real time. On your wrist, it is a calorie counter for Apple Watch and a calorie counter for Wear OS and Galaxy Watch.
