BMR Calculator – Basal Metabolic Rate (Mifflin-St Jeor)
The BMR Calculator uses the Mifflin-St Jeor equation to calculate your Basal Metabolic Rate — the number of calories your body burns at complete rest just to maintain basic functions. Enter your age, sex, height, weight, and unit system — and get your BMR in calories, a Total Daily Energy Expenditure (TDEE) estimate based on activity level, a calorie deficit target for weight loss, and a calorie surplus target for weight gain. Accurate for most adults and widely used by dietitians and fitness professionals. Formula reviewed against the Mifflin-St Jeor equation. For personalised advice, consult a qualified doctor or dietitian.
Formula
This calculator transforms the provided inputs into the requested outputs using standard domain equations.
Quick Tip
Use this output as guidance and confirm clinical decisions with a qualified professional.
How many calories does your body burn just to stay alive? That number — your BMR — is the foundation of any diet or fitness plan. Enter your details and find out in seconds.
Featured Answer
Q: How do I calculate my basal metabolic rate (BMR)?
A: BMR is calculated using the Mifflin-St Jeor equation. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. A 30-year-old woman at 60 kg and 163 cm has a BMR of approximately 1,381 calories. Use this calculator to get your result and activity-adjusted TDEE instantly.
How to Use BMR Calculator
- Enter your age in years — BMR decreases with age, so this significantly affects the result.
- Select your sex — the Mifflin-St Jeor equation uses different constants for male and female.
- Enter your height — in centimetres for metric, or feet and inches for imperial.
- Enter your weight — in kilograms for metric, or pounds for imperial.
- Select your unit system — metric or imperial.
What is Basal Metabolic Rate (BMR)?
Basal Metabolic Rate (BMR) is the number of calories your body requires to maintain basic life functions — breathing, circulation, cell production, organ function — while completely at rest. It represents your minimum daily calorie requirement just to survive, before any activity.
BMR is the foundation of calorie-based nutrition planning. Every diet or fitness goal — whether weight loss, maintenance, or muscle gain — starts here.
The Mifflin-St Jeor equation is the most widely validated formula for estimating BMR:
- Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
BMR alone is not enough for daily calorie planning — you also need your TDEE (Total Daily Energy Expenditure), which multiplies BMR by an activity factor to account for how much you move each day.
The calorie deficit for loss and calorie surplus for gain results help translate BMR and TDEE into actionable daily calorie targets.
Example: 28-year-old male, 75 kg, 178 cm, moderately active.
| Field | Value |
|---|---|
| BMR | 1,821 kcal/day |
| TDEE (moderate activity) | 2,822 kcal/day |
| Calorie Deficit for Loss | 2,322 kcal/day |
| Calorie Surplus for Gain | 3,072 kcal/day |
To lose weight, this person targets around 2,322 calories. To build muscle, around 3,072.
BMR and TDEE: The Numbers Behind Every Effective Diet Plan
Why BMR Calculator Matters
Every diet advice you have ever heard — eat less, eat more, count macros, be in a deficit — only makes sense once you know two numbers: your BMR and your TDEE.
Your BMR tells you how many calories your body needs just to exist. Your TDEE — derived from BMR and your activity level — tells you how many calories you actually burn each day in real life. Any calorie intake below TDEE creates a deficit (fat loss); above TDEE creates a surplus (muscle or weight gain).
Without these numbers, diet advice is guesswork. With them, it becomes a plan.
The Mifflin-St Jeor equation is the most widely recommended formula among clinical dietitians and sports nutrition researchers. It was validated in a 1990 study and consistently outperforms older equations like Harris-Benedict in modern populations.
How to Calculate BMR Using the Mifflin-St Jeor Equation — Step by Step
- For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
- Apply activity multiplier for TDEE:
- Sedentary (desk job, no exercise): BMR × 1.2
- Lightly active (1–3 days/week): BMR × 1.375
- Moderately active (3–5 days/week): BMR × 1.55
- Very active (6–7 days/week): BMR × 1.725
- Extra active (physical job + exercise): BMR × 1.9
- Calorie deficit for loss: TDEE − 500 (targets ~0.5 kg/week loss)
- Calorie surplus for gain: TDEE + 250 to 500 (lean muscle gain target)
Real-World Example
Showing BMR and TDEE for three different adult profiles.
| Person A | Person B | Person C | |
|---|---|---|---|
| Age / Sex | 25 / Female | 35 / Male | 45 / Female |
| Weight | 58 kg | 82 kg | 70 kg |
| Height | 162 cm | 180 cm | 168 cm |
| BMR | 1,368 kcal | 1,903 kcal | 1,497 kcal |
| Activity | Lightly active | Moderately active | Sedentary |
| TDEE | 1,881 kcal | 2,950 kcal | 1,796 kcal |
| Deficit for Loss | 1,381 kcal | 2,450 kcal | 1,296 kcal |
| Surplus for Gain | 2,131 kcal | 3,200 kcal | 2,046 kcal |
Person C is sedentary — her TDEE is relatively low despite being heavier than Person A. Her calorie target for weight loss is tight, highlighting why activity level matters so much.
Common Mistakes to Avoid
- Eating at BMR level — BMR is the minimum to stay alive at rest. Eating only your BMR number in calories is too low for most people and is not sustainable. Always calculate and eat relative to TDEE.
- Overestimating activity level — most people choose a higher activity multiplier than they actually sustain. Be honest — sedentary is more common than moderately active for desk workers.
- Treating BMR as fixed forever — BMR changes with age, body weight, and body composition. Recalculate every 3–6 months or after significant weight change.
- Using the calculator without tracking intake — knowing your TDEE is step one. Step two is actually tracking calories eaten. Without tracking, the numbers are theoretical.
- Expecting immediate results — a 500-calorie deficit creates roughly 0.5 kg per week of fat loss. Expecting 2 kg per week leads to extreme restriction and is not sustainable.
When to Use This Calculator
Use this tool at the start of any new diet or fitness plan to establish your calorie baseline. Use it again whenever your weight changes significantly — BMR shifts with body composition.
For BMI-based weight planning, the BMI Calculator – Body Mass Index gives your current BMI and healthy weight range. For pregnancy-specific calorie and weight guidance, the BMI in Pregnancy Calculator covers gestational needs.
Pro Tips
BMR calories — this is your floor, not your target. Do not eat below this number consistently without medical supervision.
TDEE estimate — this is your daily maintenance calorie level. Eating at TDEE keeps your weight stable. Adjust from here based on your goal.
Calorie deficit for loss — the standard recommendation is a 500-calorie deficit below TDEE for gradual, sustainable fat loss. This calculator uses that benchmark. Larger deficits increase muscle loss risk.
Calorie surplus for gain — for lean muscle gain, a modest 250–500 calorie surplus is recommended. Larger surpluses lead to more fat gain alongside muscle.
Important Assumptions and Limitations
The Mifflin-St Jeor equation is validated for most healthy adults but may be less accurate for very muscular or very sedentary individuals, and for those with metabolic conditions such as hypothyroidism. BMR calculation reviewed against the Mifflin-St Jeor equation (Mifflin MD et al., 1990, JADA). Activity multipliers based on standard Harris-Benedict activity factor references.
For personalised advice, consult a qualified doctor or dietitian.
Frequently Asked Questions
Find answers to common questions about BMR Calculator (Basal Metabolic Rate, Mifflin St Jeor Equation)
Basal Metabolic Rate (BMR) is the number of calories your body needs to sustain basic life functions — breathing, circulation, organ activity, and cell production — while completely at rest. It represents your minimum daily calorie requirement before any physical activity. BMR typically accounts for 60–70% of total daily calorie expenditure for sedentary individuals.
For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. For example, a 30-year-old woman at 60 kg and 163 cm: BMR = 600 + 1,018.75 − 150 − 161 = 1,308 calories. This calculator applies the formula automatically.
The Mifflin-St Jeor equation is considered the most accurate BMR formula for most healthy adults, validated in multiple studies. It is within 10% of measured BMR for most people. It may be less accurate for athletes with high muscle mass (will underestimate) and very sedentary individuals or those with metabolic conditions. For clinical precision, consult a dietitian.
TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor that accounts for how much you move each day. It represents the actual total calories you burn in a typical day. TDEE is your maintenance calorie level — eat at TDEE to maintain weight, below it to lose, above it to gain.
Recalculate every 3–6 months, or whenever your weight changes by more than 3–5 kg, you change your activity level significantly, or you pass a major age milestone. BMR decreases gradually with age and changes with body composition. Using an outdated BMR figure leads to inaccurate calorie targets as your body changes.
A deficit of 500 calories below TDEE per day is a commonly recommended target — it creates roughly 0.5 kg of fat loss per week, which is considered safe and sustainable for most adults. Larger deficits (750–1,000 calories) can cause faster loss but increase risk of muscle loss, fatigue, and nutrient deficiency. This calculator uses the 500-calorie deficit as a standard planning benchmark.
Yes, but select the correct activity multiplier and understand the limitation. Very muscular athletes tend to have higher actual BMRs than Mifflin-St Jeor predicts, because muscle tissue burns more calories at rest than fat tissue. The formula may slightly underestimate BMR for bodybuilders or high-level endurance athletes. For these cases, a sports dietitian measurement is more accurate.
BMR decreases with age, primarily due to the gradual loss of muscle mass (sarcopenia) that begins in the late 20s. The Mifflin-St Jeor formula subtracts 5 calories per year of age, meaning a 45-year-old has a BMR roughly 75 calories lower than a 30-year-old at the same weight and height. This is why calorie needs decrease with age even with the same lifestyle.