What This Calorie Calculator Does
Everything about weight management reduces to one number first: how many calories your body burns in a normal day. This calculator estimates it in two steps:
- BMR (basal metabolic rate) — what you'd burn at complete rest, from the Mifflin-St Jeor equation (the most accurate standard formula for most people).
- TDEE (total daily energy expenditure) — BMR multiplied by an activity factor for your real week.
From there it derives practical targets: maintain, lose at a sensible pace, or gain lean mass — each as an actual calories-per-day number you can act on.
The Math: Mifflin-St Jeor + Activity Multipliers
Women: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161
Then multiply by your activity level:
| Level | Multiplier | Looks like |
|---|---|---|
| Sedentary | 1.2 | Desk job, little exercise |
| Lightly active | 1.375 | Exercise 1–3 days/week |
| Moderately active | 1.55 | Exercise 3–5 days/week |
| Very active | 1.725 | Hard exercise 6–7 days/week |
| Extra active | 1.9 | Physical job + training |
Worked example — woman, 30, 165 cm, 68 kg, moderately active
TDEE = 1,400 × 1.55 ≈ 2,170 kcal/day
Setting Targets: Lose, Maintain, Gain
One pound of body fat stores roughly 3,500 kcal, so steady daily deficits/surpluses translate directly to weekly change:
| Goal | Daily adjustment | Weekly pace | Example target (TDEE 2,170) |
|---|---|---|---|
| Aggressive loss | −1000 | −2 lb (~0.9 kg) | 1,170* |
| Standard loss | −500 | −1 lb (~0.45 kg) | 1,670 |
| Mild loss | −250 | −0.5 lb | 1,920 |
| Maintain | 0 | 0 | 2,170 |
| Lean gain | +250–500 | +0.25–0.5 lb | 2,420–2,670 |
*Aggressive targets that dip near or below BMR are hard to sustain and risk muscle loss — most people do best at the standard pace. Women generally shouldn't go below ~1,200 kcal and men ~1,500 without medical supervision.
Why the Scale Fights Back: Adaptation and Accuracy
- Formulas are estimates ±10%. Track weight for 2–3 weeks at your computed maintenance; if it drifts, adjust by 100–200 kcal and re-observe.
- TDEE shrinks as you shrink. Every 5 kg lost lowers the budget — recalculate as you go.
- Metabolic adaptation is real but modest (typically 5–10% beyond weight-driven change on long diets) — diet breaks at maintenance help.
- Water masks fat. Daily weights swing 1–2 kg on sodium, carbs, and hormones — judge by weekly averages only.
- Logging errors dwarf formula errors: untracked oils, sauces and weekend meals are the usual "broken metabolism."
Making the Calories Count: Composition Basics
Calories set the direction of weight change; macronutrients shape what the change is made of:
- Protein 0.7–1 g per lb of goal body weight — preserves muscle in a deficit, builds it in a surplus, and is the most satiating macro.
- Fat minimum ~0.3 g/lb for hormonal health; fill remaining calories with carbs to fuel training.
- Fiber 25–35 g/day — the cheapest appetite control available.
Pair with resistance training in any phase — it's the signal that tells a deficit to burn fat rather than muscle. For the deeper energy-model view (with macro splits), see the TDEE Calculator; for rest-only burn, the BMR Calculator.
The Bottom Line
You don't need a perfect number — you need a starting estimate, a few weeks of honest observation, and small corrections. Compute your TDEE above, pick the sensible pace for your goal, protect protein and training, and let weekly averages tell you when to adjust. That loop, repeated, is the whole game.