For educational and tracking purposes only. Results are estimates and are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.
Calculator tool
How this calculator works
Use the explanation to understand the formula, assumptions, and practical limits behind the calculator result.
What This Calculator Computes
This calculator estimates three numbers from your physical stats and lifestyle: your Basal Metabolic Rate (BMR), your Total Daily Energy Expenditure (TDEE), and calorie targets for weight loss and weight gain. All three are derived from the same two steps.
Step 1 — Basal Metabolic Rate (Mifflin-St Jeor)
Where = weight in kg, = height in cm, = age in years.
Men:
Women:
This is the calories your body burns at complete rest. It accounts for 60–75% of total daily energy expenditure for most adults.
Step 2 — Activity Multiplier → TDEE
| Activity Level | Multiplier |
|---|---|
| Sedentary (desk job, no exercise) | ×1.2 |
| Lightly active (1–3 days/week) | ×1.375 |
| Moderately active (3–5 days/week) | ×1.55 |
| Very active (6–7 days/week) | ×1.725 |
| Extra active (physical job or 2× daily training) | ×1.9 |
TDEE is the total calories burned each day including all movement. Eating at TDEE maintains your current weight.
Step 3 — Goal Targets
- Weight loss: TDEE − 500 kcal/day → a rough planning target for gradual weight loss
- Weight gain: TDEE + 250–500 kcal/day → a rough planning target for weight gain; lean vs fat gain depends on training, protein, sleep, and genetics
These targets are starting points, not guarantees. The ~7,700 kcal per kilogram rule is a useful planning shortcut, but real body-weight change adapts over time as expenditure, appetite, water weight, and lean mass change.
Worked Example
Inputs: Female, age 28, height 163 cm, weight 65 kg, moderately active
BMR (Mifflin-St Jeor): kcal
TDEE: kcal/day
Weight loss target: kcal/day
Weight gain target: to kcal/day
How to Use These Numbers Accurately
Formula-based TDEE has a standard deviation of roughly ±200 kcal. The activity multipliers introduce additional error because self-reported activity levels are consistently overestimated — studies show people overestimate exercise intensity by 30–51%.
The most reliable approach: use this calculator to set an initial target, then track actual intake and body weight for 2–3 weeks. If weight is not moving in the expected direction, adjust calories by 100–200 kcal and reassess. The formula starts the process; real data guides it.
As weight changes, recalculate. A 10% weight loss typically reduces TDEE by 10–15%, so a fixed calorie goal becomes less accurate over time.
Common Mistakes
Eating below 1,200 kcal (women) or 1,500 kcal (men) without supervision. These are common minimum planning thresholds for adequate nutrients, not universal metabolic safety floors. Very-low-calorie diets can be clinically used in selected cases, but they need medical supervision and a plan to protect protein, micronutrients, and lean mass.
Applying a surplus without resistance training. A 500 kcal surplus without structured resistance training is more likely to produce fat gain than lean mass. Combine the surplus with a progressive lifting program.
Frequently asked questions
How accurate are calorie calculations from formulas?
The Mifflin-St Jeor equation has a standard deviation of ~200 kcal, meaning 68% of people fall within ±200 kcal of the predicted value. Activity multipliers introduce additional error because self-reported activity levels are consistently overestimated — studies show people overestimate exercise intensity by 30–51%.
Tracking actual intake for 2–3 weeks and adjusting based on body weight trend is more reliable than relying solely on the formula. Use the formula as a starting point, not a fixed prescription.
Why do calorie needs decrease as you lose weight?
As you lose weight, your body has less mass to maintain — both fat and lean mass decrease, which reduces your BMR. Additionally, metabolic adaptation lowers BMR further beyond what body composition change alone predicts (adaptive thermogenesis).
A 10% weight loss typically reduces TDEE by 10–15%, which is why a fixed calorie goal becomes less accurate over time. Recalculate your targets every 5–10 kg of weight change or whenever progress stalls for more than 2 weeks.
How does macronutrient split affect weight loss at the same calorie level?
Total calorie balance is the primary driver of weight change, but macronutrient distribution affects body composition and appetite. Protein has the highest thermic effect (25–30% of its calories are burned in digestion), preserves lean mass during a caloric deficit, and is the most satiating macronutrient per calorie.
Higher-protein diets often improve lean-mass retention and appetite control compared with lower-protein approaches at the same calorie level. The exact target depends on body size, training, kidney health, and diet pattern, so treat percentages as planning ranges rather than medical prescriptions. Carbohydrate and fat ratios matter less than hitting adequate protein and total calories.
What is the minimum safe calorie intake before metabolism is affected?
Very-low-calorie diets (VLCDs) are commonly defined as 800 kcal/day or less and are normally used only with medical supervision. They can produce rapid weight loss, but the risk profile is different from a normal calorie deficit: fatigue, nutrient gaps, gallstones, lean-mass loss, and medication adjustments may all matter.
The 1,200/1,500 kcal thresholds are practical minimums for many adults, not exact biological cutoffs. If a plan goes below them, has symptoms, involves pregnancy, diabetes medication, eating-disorder history, kidney disease, or a large weight-loss target, it should be reviewed by a clinician or registered dietitian.
