BMR
Calculator
Calculate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) using the Mifflin-St Jeor equation — with activity-adjusted calorie targets, macros, and goal-based recommendations.
—
BMR Calculator: Calculate Your Daily Calorie Needs
Understanding how many calories your body actually needs — not from a generic chart, but from your specific age, height, weight, gender, and activity level — is the foundation of any successful nutrition strategy. This free BMR calculator uses the Mifflin-St Jeor equation, the most accurate widely-used formula for predicting resting metabolic rate, to compute your Basal Metabolic Rate and Total Daily Energy Expenditure in seconds. It then generates calorie targets for five different goals — from mild fat loss to muscle gain — along with macronutrient recommendations and a visual breakdown of where your daily calories go.
🔥 Mifflin-St Jeor formula:
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
TDEE = BMR × Activity multiplier (1.2 to 1.9)
How the BMR Calculator Formula Works
This calculator measures two numbers: how many calories your body burns doing nothing (BMR), and how many calories you actually need in a typical day once activity is factored in (TDEE). The Mifflin-St Jeor formula takes your weight, height, and age, combines them with a fixed gender adjustment, and produces BMR in calories per day. Multiplying that by an activity multiplier between 1.2 and 1.9 gives TDEE. The units are always kilocalories per day (what’s usually just called “calories” on nutrition labels). Read BMR as your calorie floor: the energy cost of simply staying alive. Read TDEE as your maintenance number: eating this many calories keeps your weight stable. The formula assumes an average body composition for your age, weight, and height. It doesn’t know your actual muscle mass, so two people with the same stats but very different muscle-to-fat ratios will have somewhat different real BMRs even though the formula gives them the same number.
Identify the inputs
You enter age, gender, weight, and height, then pick the activity level that best matches your typical week.
Apply the formula
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age), then add 5 for men or subtract 161 for women.
Perform the calculation
Using the calculator’s default example, a 30-year-old man at 75kg and 175cm: (10 × 75) + (6.25 × 175) − (5 × 30) + 5 = 750 + 1,093.75 − 150 + 5 = 1,698.75, rounding to 1,699 kcal/day.
Interpret the result
1,699 kcal/day is what this person burns at complete rest. Multiplying by the moderate activity multiplier (1.55) gives a TDEE of about 2,633 kcal/day, the calorie level that maintains his current weight given his activity level.
3 Real-Life Examples
1. A desk worker starting a mild calorie deficit
A 35-year-old man weighing 85kg and 178cm tall, with a sedentary desk job and no regular exercise, wants to lose weight gradually.
At the mild deficit goal (−275 kcal/day), his target becomes 1,876 kcal/day, aiming for roughly 0.25kg of weight loss per week, a pace that’s easier to sustain than a steeper cut.
2. A very active woman checking her maintenance calories
A 28-year-old woman who trains hard 6 to 7 days a week weighs 62kg and is 165cm tall, and wants to know how much she can eat without gaining or losing weight.
Her high training volume means activity accounts for nearly 42% of her total daily calories, well above what a sedentary person’s activity level would contribute, illustrating why the activity multiplier matters as much as BMR itself for very active people.
3. A young trainee planning a lean muscle-building phase
A 22-year-old man who exercises moderately, weighing 70kg and 180cm tall, wants to gain muscle without excessive fat gain.
At the standard bulk goal (+550 kcal/day), his target becomes 3,216 kcal/day. Combined with resistance training and adequate protein, this moderate surplus supports muscle growth while limiting the fat gain that comes with a larger, more aggressive surplus.
What Is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body burns per day while at complete rest — doing absolutely nothing beyond sustaining essential biological functions: breathing, circulation, temperature regulation, organ function, and cellular repair. Think of it as the minimum energy cost of being alive.
BMR typically accounts for 60–75% of total daily calorie expenditure, making it by far the largest single component of your energy needs. Even if you spend an entire day lying motionless in bed, your body would still burn your BMR worth of calories just keeping its systems running. This is why BMR is the foundation of all personalised calorie calculations — getting this number right is more important than any other variable in nutrition planning.
BMR vs TDEE: What’s the Difference?
TDEE (Total Daily Energy Expenditure) is your complete daily calorie burn — BMR plus everything else: the energy used for digesting food (thermic effect of food, approximately 10% of intake), non-exercise movement like walking and fidgeting (NEAT), and planned exercise (EAT). TDEE is your maintenance calorie level — eating exactly this amount keeps your weight stable.
| Component | What it is | % of TDEE | Controlled by |
|---|---|---|---|
| BMR | Calories at complete rest | 60–75% | Body composition, age, gender |
| TEF | Digestion and food processing | ~10% | Diet composition |
| NEAT | Non-exercise movement | 15–50% | Lifestyle, occupation |
| EAT | Planned exercise | 5–15% | Training volume/intensity |
The most variable component — and one of the most underestimated — is NEAT. Non-exercise activity thermogenesis can vary by as much as 1,000 kcal/day between two people of identical weight and training volume, based purely on how much they move during daily life. This explains why some people seem to “eat anything” without gaining weight — they often have very high NEAT from occupational or habitual movement.
Activity Multipliers: Choosing the Right Level
Your TDEE is calculated by multiplying your BMR by an activity factor. Choosing the correct multiplier is the largest source of error in TDEE estimation, particularly since most people overestimate their activity level relative to the CDC’s baseline physical activity guidelines for adults (150 minutes of moderate activity per week), especially those who exercise but work desk jobs.
Sedentary (×1.2)
Desk job, drives to work, minimal walking, no planned exercise. Many people who consider themselves “not very active” actually fall here. Typical calorie add above BMR: 20% — the smallest multiplier, appropriate for truly sedentary days.
Lightly active (×1.375)
Light exercise 1–3 days per week, walking for 30–45 minutes most days, or a modestly active job. The correct level for casual gym-goers who don’t train intensely or frequently.
Moderately active (×1.55)
Exercise 3–5 days per week at moderate intensity, or a physically active job. The most common correct category for regular gym-goers. Burns approximately 55% above BMR in total.
Very active / Athlete (×1.725–1.9)
Hard exercise 6–7 days per week, twice-daily training, or a demanding physical job (construction, sports coaching, military). Reserve these multipliers only for genuinely high training loads — most recreational athletes overestimate and should use 1.55.
BMR and Weight Loss
For fat loss, you need to consume fewer calories than your TDEE — creating a calorie deficit. The appropriate deficit size depends on how aggressively you want to lose fat, your current body composition, and your tolerance for dietary restriction:
- Mild deficit (−275 kcal/day): ~0.25 kg fat loss per week. The most sustainable approach — minimal hunger, minimal muscle loss risk, easiest to maintain long-term. Ideal for those already lean or new to structured dieting.
- Moderate deficit (−550 kcal/day): ~0.5 kg fat loss per week. The research-supported sweet spot for most people — fast enough to see consistent progress, sustainable for months with adequate protein and resistance training.
- Aggressive deficit (−750 to −1000 kcal/day): ~0.75–1 kg fat loss per week. Appropriate only for limited periods or clinical settings. Increases risk of muscle loss, metabolic adaptation, nutrient deficiency, and poor adherence. Always pair with high protein and resistance training.
Critically, the calorie floor matters — this calculator enforces a minimum of 1,200 kcal/day. Going below this consistently increases the risk of significant muscle loss, micronutrient deficiencies, and metabolic adaptation that makes future weight management harder.
BMR and Muscle Gain
Building muscle requires a calorie surplus — consuming more than your TDEE to provide the energy and building materials for muscle protein synthesis. The appropriate surplus is smaller than most people assume:
- Lean bulk (+275 kcal/day): Very slow muscle gain (~1–2 kg/year for trained individuals) with minimal fat gain. Best for those who want to optimise body composition.
- Standard bulk (+550 kcal/day): Moderate muscle gain with some fat accumulation. Practical for beginners and intermediate trainees who can gain faster than advanced athletes.
Research consistently shows that natural trainees cannot gain muscle faster than approximately 0.5–1 kg per month in ideal conditions (beginners) or 0.25–0.5 kg per month (intermediate trainees). Larger surpluses beyond these rates simply produce more fat gain without accelerating muscle growth.
Factors That Affect Your BMR
- Body composition: Muscle tissue burns approximately 3× more calories at rest than fat tissue. Two people of identical weight but different body composition (one muscular, one with higher body fat) will have meaningfully different BMRs.
- Age: BMR declines approximately 1–2% per decade from the mid-20s onwards, primarily due to age-related muscle loss (sarcopenia). This is one of the strongest arguments for resistance training as we age — preserving muscle mass preserves metabolic rate.
- Gender: Men typically have higher BMRs than women of similar age and weight, primarily due to higher average muscle mass and different hormonal profiles. The Mifflin-St Jeor formula accounts for this with the +5/−161 gender adjustment.
- Hormones: Thyroid hormones directly regulate metabolic rate. Hypothyroidism (underactive thyroid) can reduce BMR by 10–40%. Other hormones — cortisol, insulin, sex hormones — also influence metabolic rate and nutrient partitioning.
- Genetics: Some individuals have naturally higher or lower metabolic rates than predicted by anthropometric formulas. This accounts for why calculator estimates should be validated against real-world results over 2–4 weeks of consistent tracking.
Important Notes
What this calculator does and doesn’t cover
This tool applies the Mifflin-St Jeor formula to the numbers you enter. A few things worth understanding before relying on the results:
- Population-average formula, not a measurement. Mifflin-St Jeor predicts BMR within about ±10% for roughly 80% of people compared to lab-measured resting metabolic rate. Your actual number could sit outside that range.
- The activity multiplier is the biggest source of error. Most people overestimate how active they genuinely are. If your weight trend doesn’t match the calculator’s prediction after 2 to 4 weeks of consistent tracking, adjust the calorie target rather than assuming the BMR figure itself is wrong.
- The protein target uses a flat 2g per kg of body weight, a reasonable general guideline, not a personalized recommendation accounting for training status, body composition goals, or medical conditions.
- Macros are calculated using fixed assumptions (roughly 28% of calories from fat, protein at 2g/kg, remaining calories from carbohydrate, with a 50g carbohydrate floor), not tailored to any specific diet approach or personal preference.
- A 1,200 kcal/day floor is enforced on the goal calorie targets, since going meaningfully below this on a sustained basis raises the risk of nutrient deficiency and muscle loss regardless of what a deficit calculation suggests.
- Not medical or dietary advice. For personalized guidance, especially with existing health conditions, pregnancy, or significant dietary changes, consult a registered dietitian or healthcare provider. The NIH’s Body Weight Planner offers a more detailed, personalized modeling tool for weight management planning.
Related Nutrition & Fitness Calculators
Frequently Asked Questions
Calculate your BMR now
BMR, TDEE, calorie targets, macros — science-based, free, and instant.
Calculate my BMR ↑