TDEE (Total Daily Energy Expenditure) is the number of calories your body burns in a 24-hour day. It's the most important number in fat loss math: eat below your TDEE consistently and you lose fat. The hard part is calculating it accurately.
Here's how the math works, and why every other calculator is probably lying to you.
The standard formula
Every TDEE calculator follows the same two-step structure:
BMR = energy you'd burn lying in bed all day
TDEE = BMR × activity multiplier
Step 1: BMR
The standard formula is Mifflin–St Jeor (1990), which the Academy of Nutrition and Dietetics recommends as the most accurate equation:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
CalBurndown uses Mifflin–St Jeor as the BMR floor.
Step 2: Activity multiplier
This is where most calculators go wrong. The classic table:
| Lifestyle | Multiplier |
|---|---|
| Sedentary (desk job, no exercise) | 1.2 |
| Lightly active (light exercise 1-3 days/wk) | 1.375 |
| Moderately active (4-5 days/wk) | 1.55 |
| Very active (daily intense exercise) | 1.725 |
| Extra active (manual labor + training) | 1.9 |
You pick a row, multiply BMR by that number, and call it TDEE.
Why this is wrong
Two problems:
-
Self-reported activity is wildly inaccurate. Studies consistently show people overestimate their own activity by 30-50%. "Moderately active" feels true; it usually isn't.
-
One multiplier can't capture daily variance. Your TDEE on a 15,000-step day is meaningfully different from a 4,000-step day. A single number averages everything together — and the average is dominated by what you do most days, which is usually less than you think.
The result: classic TDEE calculators systematically overestimate, especially for sedentary office workers who occasionally lift weights. People then eat at "their TDEE minus 500" and don't lose weight.
What CalBurndown does instead
Instead of asking you to self-categorize, we measure activity directly:
TDEE = BMR + active calories actually burned today
Where "active calories" come from:
- Manual exercise logs — walks, runs, rucks, strength sessions
- Watch sync — steps, workouts, HR (coming with the mobile apps)
- Photo / voice logs — incidental movement you mention
We then calibrate against your weight changes every two weeks. If you're losing slower or faster than predicted, we adjust your BMR multiplier (clamped to ±15% to stay sane). After 4-6 weeks of data, this is more accurate than any static TDEE calculator.
See TDEE calibration for how that loop works.
Quick sanity check
Want a quick approximation right now? Here's a rough TDEE estimator that's better than the standard multiplier table:
TDEE ≈ BMR + (steps × per-step kcal) + planned exercise
Where per-step kcal scales with your body weight:
| Weight | kcal per 1,000 steps |
|---|---|
| 120 lb | 30 |
| 160 lb | 40 |
| 200 lb | 50 |
| 240 lb | 60 |
Example: 175 lb man, 6,000 daily steps, occasional 30-min lifting session = 1,750 (BMR) + 6,000 × 0.044 (~265) + 200 (lifting) = ~2,215 kcal TDEE.
That's ~10-15% below what the "moderately active × 1.55" calculator would say — and probably closer to your real number.
In CalBurndown
Your TDEE is the top of the burndown chart before deficit subtraction. Numbers we use:
- BMR — Mifflin–St Jeor with your stored body stats
- Active — sum of today's logged activities
- Calibration factor — ±15% multiplier on BMR, recomputed every 2 weeks from your weight trend
You don't need to enter an "activity level." Just log what you do; we'll compute the rest.