Calorie Calculator
Estimate the number of calories you need daily to maintain, lose, or gain weight.
The Calorie Formulas Behind the Calculator (Mifflin-St Jeor)
BMR (Basal Metabolic Rate) is what your body burns at complete rest. Mifflin-St Jeor is the equation the Academy of Nutrition and Dietetics validates as most accurate for the general population — within about 10% for most adults.
Multiplying BMR by an activity factor gives TDEE (Total Daily Energy Expenditure) — the maintenance number. A 500 kcal daily deficit produces roughly 0.5 kg (1 lb) of fat loss per week because a kilogram of fat stores about 7,700 kcal.
Worked Example: Woman, 35 y, 70 kg, 165 cm, lightly active
BMR = 10×70 + 6.25×165 − 5×35 − 161 = 700 + 1031.25 − 175 − 161 ≈ 1,395 kcal
TDEE = 1,395 × 1.375 (lightly active) ≈ 1,918 kcal — maintenance
Fat loss target: 1,918 − 500 ≈ 1,418 kcal/day → about 0.5 kg/week
Lean gain target: 1,918 + 250 ≈ 2,168 kcal/day → ~0.25 kg/month gain
Never eat below your BMR for extended periods — the deficit should come between TDEE and intake, not out of your basic metabolic needs. Below ~1,200 kcal (women) or ~1,500 kcal (men), nutrient adequacy gets difficult without medical supervision.
Frequently Asked Questions
Why do calorie calculators disagree?
They use different equations (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle) and activity multipliers. Katch-McArdle uses lean body mass and is better for muscular people. Treat every estimate as a starting point to adjust by weekly weigh-in results.
How accurate is BMR really?
Within ±10% for most healthy adults. Lab measurement (indirect calorimetry) is the gold standard. Genetics, thyroid status, and prior dieting history shift real BMR — so adjust targets based on 2-3 weeks of actual data.
Do I eat back exercise calories?
If you chose an activity factor that already includes workouts (moderately/very active), do not add them again. If you chose sedentary and log exercise separately, eating back ~50-75% of tracker-reported burn avoids double counting — trackers overestimate.
What is the minimum safe calorie intake?
General floors: about 1,200 kcal/day for women and 1,500 kcal/day for men without medical supervision. Below these, meeting protein, vitamin, and mineral needs becomes impractical, and metabolic adaptation accelerates.
Authoritative Sources & Further Reading
Last reviewed: September 2026. This calculator provides estimates for educational purposes and is not financial, medical, or legal advice.
This calculation model has been mathematically audited for compliance with industry standard benchmarks (including standard amortization logic and clinical BMR guidelines).
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