Calorie Calculator: BMR & TDEE Using Mifflin-St Jeor
Enter your sex, age, weight, height, and activity level to get your Basal Metabolic Rate and Total Daily Energy Expenditure from the Mifflin-St Jeor equation, plus daily calorie targets to lose, maintain, or gain weight. Free and 100% client-side.
Calorie estimates are population averages, not medical advice. Individual metabolism varies by body composition, genetics, medications, hormones, and dozens of other factors. For weight-loss, performance, or medical-condition planning, consult a registered dietitian or physician.
Mifflin-St Jeor BMR
Uses the equation the American Dietetic Association recommends — more accurate than the older Harris-Benedict for non-obese adults. Metric and imperial input supported.
Five Activity Levels
Sedentary, light, moderate, very active, extra active — each with a clear definition. Multiplier ranges from 1.2 (desk job) to 1.9 (physical labour + hard training).
Per-Goal Calorie Targets
See the daily calories for each common goal: lose 1 lb / 0.5 lb per week, maintain, gain 0.5 lb / 1 lb per week. Based on the 3,500 kcal ≈ 1 lb fat approximation.
100% Client-Side
Personal stats (weight, height, age, sex) stay entirely in your browser. No upload, no logging, no analytics tied to your numbers.
How this calorie calculator works
This calorie calculator computes your Basal Metabolic Rate (BMR) with the Mifflin-St Jeor equation, then multiplies it by an activity factor to get your Total Daily Energy Expenditure (TDEE). From TDEE it derives daily calorie targets: subtract 500 kcal to lose 1 lb/week, add 500 to gain 1 lb/week. It takes sex, age, weight, and height, runs entirely in your browser, and shows every number side by side.
It uses Mifflin-St Jeor because the Academy of Nutrition and Dietetics (formerly the American Dietetic Association) recommends it as the most reliable prediction equation for healthy adults. The older Harris-Benedict equation from 1919 overstates BMR by 5–10% for modern populations. Cross-check your results with the BMI calculator for a weight-status screen, the body fat calculator for composition, and the water intake calculator for a daily hydration target.
The exact formula this calculator uses
BMR is calculated with the Mifflin-St Jeor equation (1990). Weight is in kilograms, height in centimetres, and age in years; imperial inputs are converted to metric first (1 lb = 0.45359237 kg, 1 in = 2.54 cm). The only difference between sexes is the final constant.
BMR (men) = 10 · kg + 6.25 · cm − 5 · age + 5
BMR (women) = 10 · kg + 6.25 · cm − 5 · age − 161
TDEE = BMR × activity factor
Goal kcal = TDEE ± (500 per 1 lb/week, 250 per 0.5 lb/week)
- kg — body weight in kilograms
- cm — height in centimetres
- age — age in whole years
- +5 / −161 — the sex constant (men add 5, women subtract 161)
- activity factor — 1.2 (sedentary) to 1.9 (extra active); see the table below
The equation comes from Mifflin MD, St Jeor ST, et al., "A new predictive equation for resting energy expenditure in healthy individuals", American Journal of Clinical Nutrition 1990;51(2):241–247 (PMID 2305711), derived from 498 healthy adults aged 19–78 and validated to within roughly ±10% of indirect-calorimetry measurements.
Worked example: 30-year-old man, 80 kg, 180 cm, moderately active
Plug a 30-year-old man weighing 80 kg at 180 cm, moderately active (×1.55), into the formula step by step:
- 10 · 80 = 800
- 6.25 · 180 = 1,125
- 5 · 30 = 150
- BMR = 800 + 1,125 − 150 + 5 = 1,780 kcal/day
- TDEE = 1,780 × 1.55 = 2,759 kcal/day
- Lose 1 lb/week = 2,759 − 500 = 2,259 kcal/day
- Gain 1 lb/week = 2,759 + 500 = 3,259 kcal/day
Those are the exact numbers the calculator returns for the same inputs: BMR 1,780, TDEE 2,759, with goal targets of 2,259, 2,509, 2,759, 3,009, and 3,259 kcal across the five goals. Numbers are rounded to the nearest whole calorie.
The Five Activity Multipliers, Defined
| Level | Multiplier | Definition |
|---|---|---|
| Sedentary | ×1.2 | Desk job, no formal exercise; under 5,000 steps/day |
| Lightly active | ×1.375 | Light exercise 1–3 days/week; 5,000–7,500 steps/day |
| Moderately active | ×1.55 | Moderate exercise 3–5 days/week; 7,500–10,000 steps/day |
| Very active | ×1.725 | Hard exercise 6–7 days/week; 10,000–12,500 steps/day |
| Extra active | ×1.9 | Physical job + daily training; 12,500+ steps/day |
Most people self-select one bracket too high. Be honest: if you spend 8+ hours seated, your baseline is sedentary regardless of a 45-minute gym session.
Calories per Gram by Macronutrient
| Macro | kcal / gram | Note |
|---|---|---|
| Protein | 4 | Most filling per calorie |
| Carbohydrate | 4 | Includes sugars, starches, fibre |
| Fat | 9 | Most energy-dense; essential for hormones |
| Alcohol | 7 | Often forgotten in daily totals |
| Fibre (subset) | 2 | Partially digested; counted as ~2 kcal/g |
Knowing these conversion factors lets you sanity-check any nutrition label. The big shock for most people: fat at 9 kcal/g is more than twice as calorie-dense as protein or carbs (4 kcal/g). Olive oil isn't bad — one tablespoon is a normal portion — but it's 120 kcal in a portion you can barely see.
Six Calorie-Tracking Mistakes (and Fixes)
1. Eyeballing Portions
Studies show free-pour cooking oil ranges 2–6× the eyeballed amount. Buy a $15 kitchen scale; weigh anything calorie-dense for two weeks until your eye recalibrates.
2. Activity-Level Inflation
Honest defaults: most office workers with 3-4 gym sessions/week are "lightly active", not "moderate". The lower bracket usually fits.
3. Liquid Calorie Blindness
A 16 oz oat-milk latte is 220 kcal. Two per day is a 440-kcal silent surplus — enough to offset an entire daily deficit.
4. Weekend Reset
A 500-kcal weekday deficit + 1000-kcal weekend surplus = net zero. Track Friday-Sunday as carefully as Mon-Thu.
5. Trusting Restaurant Calories
FDA studies show restaurant menu calorie counts vary ±20% from the listed value, almost always in the higher direction. Add a buffer.
6. Aggressive Deficits
Cuts deeper than 25% below TDEE accelerate muscle loss, hormonal drops, and bingeing. 500 kcal/day below TDEE is the sustainable floor for most adults.
The limit no calculator can fix
Mifflin-St Jeor predicts BMR to within roughly ±10% for any individual, which means a calculated 1,780 kcal could be anywhere from about 1,600 to 1,960 in real life. The equation uses only weight, height, age, and sex — it cannot see body composition. Two people at the same weight differ in BMR because muscle burns more at rest than fat, so a lean, muscular person sits at the high end of the range and a higher-body-fat person at the low end.
If you know your body-fat percentage to within ±2% (from a DEXA scan or caliper reading), the Katch-McArdle equation — BMR = 370 + 21.6 · lean mass in kg — is tighter for very lean or very muscular bodies. For everyone else, treat this output as a starting point: track weight and intake for 2–4 weeks, then adjust by 100–200 kcal if the trend is off.
Frequently asked questions
What is BMR and how is it calculated?
BMR (Basal Metabolic Rate) is the calories your body burns at rest for breathing, circulation, and cell repair. This tool uses Mifflin-St Jeor (1990): BMR = 10·kg + 6.25·cm − 5·age, then +5 for men or −161 for women.
What is the difference between BMR and TDEE?
BMR is calories burned at rest; TDEE is BMR multiplied by an activity factor that accounts for all daily movement. A desk worker is roughly BMR × 1.2; a daily hard trainer is BMR × 1.9. Use TDEE, not BMR, as your daily calorie reference.
How accurate are calorie calculators?
Within about ±10% for any individual. Genetics, body composition, hormones, medications, and sleep all shift real metabolism. Track weight and intake for 2–4 weeks, then adjust calories by 100–200 if the trend is off.
Why a 500-calorie deficit for 1 lb/week?
One pound of body fat is roughly 3,500 kcal, so 500 kcal/day × 7 days ≈ 3,500 kcal = 1 lb. It is an approximation — actual loss includes water and lean tissue, and metabolism adapts — but 500 kcal/day is the sustainable floor for most adults.
Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor. Harris-Benedict (1919) was built from 239 mostly young, male, European adults and overstates BMR by 5–10% today. Mifflin-St Jeor (1990) used a larger, more diverse cohort and matches indirect calorimetry more closely.
Is my personal health data sent to a server?
No. Every calculation runs in your browser with JavaScript. Weight, height, age, sex, and activity level never leave your device — no upload, no logging, no analytics tied to your numbers.
How do I calculate calories for muscle gain vs fat loss?
Fat loss: TDEE − 250 to 500 kcal/day, with the smaller deficit preserving more muscle. Lean gain: TDEE + 250 to 500 kcal/day with protein at 1.6–2.2 g/kg and resistance training. Bigger surpluses just add fat. Set a protein target separately — calories alone do not decide muscle vs fat.
Why isn't my recommended calorie intake working?
Usually one of four things: under-counting intake by 20–30%, overstating your activity level, metabolic adaptation lowering BMR by 5–10% during long deficits, or genetic variance. Log everything for two weeks, then make small changes — drop 100 kcal or add a daily walk, not dramatic cuts.
Does this calculator account for body composition?
No — Mifflin-St Jeor uses only weight, height, age, and sex. For very lean or very muscular bodies, Katch-McArdle (BMR = 370 + 21.6 · lean mass in kg) is tighter, but it needs a body-fat measurement most people do not have.
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For general informational purposes only — not medical advice. Calorie estimates are population averages and vary by individual. Consult a healthcare provider or registered dietitian before making decisions about weight loss, performance nutrition, or any medical condition.
Last reviewed: June 2, 2026 · Formula source: Mifflin et al. 1990, recommended by the Academy of Nutrition and Dietetics · Runs 100% in your browser — no uploads, nothing leaves your device.
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