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Calorie Calculator

Estimate daily calories with the Mifflin–St Jeor equation. Five activity multipliers, six cut/bulk goals, suggested protein / fat / carb split and an expected weekly weight change. Metric and imperial. Free, private, with explicit "not medical advice" caveats.

What is the Calorie Calculator?

A calorie calculator estimates how many kilocalories you burn in a day and how much to eat for a goal — maintenance, weight loss or weight gain. Toollyz Calorie Calculator uses the Mifflin–St Jeor equation (1990) — the Academy of Nutrition and Dietetics's preferred BMR formula for healthy adults: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5 (male) or − 161 (female). Multiply by an activity factor (1.20 sedentary, 1.375 light, 1.55 moderate, 1.725 very active, 1.90 extra active) to get TDEE, then apply a goal delta (Aggressive cut −750, Standard cut −500, Mild cut −250, Maintain ±0, Mild bulk +250, Standard bulk +500 kcal/day) to get the target intake. The component supports both metric (kg + cm) and imperial (lb + ft + in) with exact unit conversions (1 lb = 0.45359237 kg, 1 in = 0.0254 m). A live macro panel suggests 1.8 g protein per kg of body weight, 25% of calories from fat and the rest from carbs. The expected weekly weight change uses 7,700 kcal per kg of body fat. The Not Medical Advice panel is prominently displayed: Mifflin–St Jeor estimates a population average with ±10–15% individual variation; the 7,700 kcal/kg rule ignores water, glycogen and lean tissue; pregnant, nursing, ill or athlete users should talk to a clinician. Toollyz has no backend; inputs save to localStorage.

How to use it

  1. Pick Metric or Imperial and fill in sex, age, weight and height.
  2. Choose an activity level (Sedentary → Extra active).
  3. Pick a goal (Aggressive / Standard / Mild cut, Maintain, Mild / Standard bulk) — the target intake updates live.
  4. Read your suggested macros and expected weekly weight change.

Benefits

  • Mifflin–St Jeor BMR — the most validated equation for the general population.
  • Five activity multipliers spanning desk workers to heavy training + manual labour.
  • Six goal presets covering aggressive cuts through standard bulks.
  • Macro split based on 1.8 g protein per kg, 25% fat, balance carbs.
  • Weekly weight-change estimate using the 7,700 kcal-per-kg rule of thumb.
  • Metric (kg + cm) and imperial (lb + ft + in) inputs with exact unit conversions.
  • Honest "not medical advice" caveats panel — algorithms are population statistics, not diagnostics.
  • 100% private — Toollyz has no backend, inputs save to localStorage on this device only.

Frequently asked questions

What's BMR?

Basal Metabolic Rate — the energy your body burns at complete rest just keeping you alive (organs, ion pumps, basal cell function). Mifflin–St Jeor is the most accurate estimate for healthy adults; Harris–Benedict and Katch–McArdle are older or require body-fat percentage.

What's TDEE?

Total Daily Energy Expenditure — BMR plus everything else you do (walking, thinking, fidgeting, formal exercise). Toollyz uses the standard activity multipliers from 1.20 (sedentary) to 1.90 (extra active) on top of BMR.

What activity level should I pick?

Sedentary = desk job, no real exercise. Light = light activity 1–3 days/week (walks, casual yoga). Moderate = 3–5 sessions/week with real intensity. Very active = 6–7 sessions/week or daily training. Extra active = heavy training plus a physical job. People often over-estimate — pick the level below your gut feeling for a more honest target.

Why do men and women have different equations?

Lean body mass differs on average between sexes, so the equation has a different constant: +5 for males and −161 for females, both in kcal/day. The rest of the formula is identical.

How accurate is the BMR estimate?

Studies show Mifflin–St Jeor is within ±10% of measured BMR for about 80% of healthy adults. Outliers (very lean, very muscular, very old, very young) can be ±15% or more. Don't treat the number as gospel — adjust intake based on actual scale weight over 2–3 weeks.

What about the "7,700 kcal per kg" rule?

It comes from the energy density of human adipose tissue and applies cleanly only to body fat. Real-world weekly weight changes also include water (glycogen + sodium), undigested food, hormonal cycles and the lean tissue you gain during a bulk. Treat the weekly-change number as a long-run average over weeks, not a daily target.

Why suggest 1.8 g protein per kg?

It's in the middle of the evidence-based range (1.6–2.2 g/kg for active adults) and supports both muscle retention during a cut and muscle gain during a bulk. People with kidney disease should consult a doctor before going high-protein.

Is the macro split a hard rule?

No — it's a starting point. Many people thrive on lower fat / higher carb or vice versa. Toollyz fixes protein and fat (25% calories) and lets carbs fill the rest because that's a balanced starting point most evidence-based nutrition guides endorse.

Can I use this for pregnancy or breastfeeding?

No. Pregnancy and lactation change energy needs in ways the standard equations don't capture. Use a pregnancy-specific calculator with a clinician's input.

Is this Calorie Calculator free?

Completely free with no signup and no limits. Compute as many estimates as you like — privately in your browser. Toollyz has no backend.

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