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BMR Calculator: Estimate Your Resting Calorie Burn

Estimate your basal metabolic rate using the Mifflin-St Jeor formula

HealthBy Numora health teamReviewed by Numora editorial review board, Registered Dietitian (RD)Updated Peer-reviewed

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Reviewed against primary sources.

Assumptions
years
lb
in
Basal Metabolic Rate (BMR)
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Fill in the 3 fields above to see your result.

BMR estimates are population averages and may differ ±10% from your individual metabolism. For weight-management decisions affecting medical conditions, consult a registered dietitian or physician.

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⚡ The answer

BMR (Basal Metabolic Rate) is the energy your body uses at complete rest for vital functions like heart, brain, and breathing. The Mifflin-St Jeor equation estimates BMR from age, sex, weight, and height with ~95% accuracy in healthy adults. Multiply BMR by an activity factor (1.2 sedentary to 1.9 very active) for total daily calorie needs.

Quick takeaway

**A 30-year-old, 178 cm, 75 kg male has a BMR of about 1,667 kcal/day** using the Mifflin-St Jeor formula. This represents the calories your body burns at complete rest. To estimate total daily calorie needs (TDEE), multiply your BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active). The Mifflin-St Jeor formula is population-validated to within ±10% for healthy adults, but individual variation can move the true number up or down by 100–200 kcal/day. Always track your actual weight changes to fine-tune your calorie targets.

What is a bmr?

Use this BMR calculator to accurately estimate your basal metabolic rate (BMR) — the essential calories your body burns at complete rest to maintain vital functions. Our tool employs the Mifflin-St Jeor equation, widely recognized as the consensus formula in clinical and sports-nutrition references since 1990 for its superior accuracy. Enter your biological sex, age, weight in kilograms, and height in centimeters. The calculator will provide your BMR, along with five activity-adjusted daily calorie targets to help you estimate your Total Daily Energy Expenditure (TDEE). This method is rigorously validated against indirect calorimetry in published Academy of Nutrition and Dietetics evidence reviews, offering a reliable starting point for your nutritional planning.

The formula

BMR = 10·W + 6.25·H − 5·A + S (S = +5 male, −161 female)
  • W — weight in kilograms
  • H — height in centimeters
  • A — age in years
  • S — sex constant (+5 for male, −161 for female)

Source: Mifflin-St Jeor equation (1990).

Worked examples

1Median male, 30 years, 75 kg, 178 cm

Inputs
sex: maleage: 30weight: 75height: 178
Walkthrough

BMR = 10×75 + 6.25×178 − 5×30 + 5 = 750 + 1,112.5 − 150 + 5 = 1,667.5 kcal/day. Sedentary TDEE = 2,001; lightly active = 2,293; very active = 2,876. For weight maintenance with a typical office job + 3 weekly gym sessions, target ~2,584 kcal/day.

2Median female, 30 years, 62 kg, 165 cm

Inputs
sex: femaleage: 30weight: 62height: 165
Walkthrough

BMR = 10×62 + 6.25×165 − 5×30 − 161 = 620 + 1,031 − 150 − 161 = 1,340 kcal/day. The female sex offset (−161) plus typically lower weight produces a meaningfully smaller BMR than the male example with proportionally similar inputs. TDEE at moderate activity (1.55) ≈ 2,077 kcal/day.

3Older adult, 65 years, 80 kg, 175 cm

Inputs
sex: maleage: 65weight: 80height: 175
Walkthrough

BMR = 10×80 + 6.25×175 − 5×65 + 5 = 800 + 1,093.75 − 325 + 5 = 1,574 kcal/day. For comparison, the same body at age 30 would have a BMR of 1,749 — a 175 kcal/day difference. Resistance training to preserve lean mass is the single largest reversible factor.

How to use this calculator

  1. Sex — Biological sex affects the equation constant; the Mifflin-St Jeor adjustment is +5 for males, −161 for females.
  2. Age — Your age in whole years. BMR drops gradually with age — about 1–2% per decade after 20.
  3. Weight — Body weight in kilograms. Multiply pounds by 0.4536 to convert.
  4. Height — Height in centimeters. Multiply inches by 2.54 to convert.
  5. Read the result. Use the worked examples below to sanity-check against a known scenario.

What your result means and what to do next

If above
A BMR significantly above the typical range for your demographic might indicate a higher-than-average lean body mass, intense physical activity, or potentially a hypermetabolic state (e.g., hyperthyroidism, fever). Ensure your inputs are correct, especially weight and height.
If below
A BMR significantly below the typical range could suggest lower lean body mass, a sedentary lifestyle, or potentially a hypometabolic state (e.g., hypothyroidism). Double-check that you've used kilograms for weight and centimeters for height, as incorrect units are the most common cause of low readings.
When to escalate
If your BMR consistently seems much higher or lower than expected, or if you experience unexplained weight changes, fatigue, or other symptoms, consult a registered dietitian or physician. They can help rule out underlying medical conditions or recommend indirect calorimetry for a precise measurement.

Common mistakes and edge cases

Using Imperial Units in Metric Fields

The Mifflin-St Jeor equation requires weight in kilograms and height in centimeters. A common error is entering pounds or inches directly, which will produce drastically incorrect (usually very low) BMR values. Always convert your measurements to metric before inputting them into the calculator.

Overestimating Activity Level

Many people overestimate their daily activity. A desk job with 2-3 light workouts per week is often 'lightly active' or even 'sedentary' by clinical definitions, not 'moderately active.' Being honest about your activity multiplier is crucial for an accurate TDEE estimate; when in doubt, choose a lower activity level.

Expecting Exact Results Without Adjustment

BMR equations provide population averages, not precise individual measurements. Your actual BMR can vary by ±10% from the calculated value due to genetic factors, body composition, and other variables. Use the calculator as a starting point, then track your weight and adjust your calorie intake iteratively over 2-3 weeks to find your true maintenance needs.

Eating Below Your BMR for Weight Loss

While a calorie deficit is necessary for weight loss, consistently eating below your Basal Metabolic Rate is generally not recommended. This can lead to excessive lean muscle loss, nutrient deficiencies, hormonal imbalances, and an unsustainable level of hunger, often resulting in rebound weight gain. Aim for a deficit relative to your Total Daily Energy Expenditure (TDEE), typically 250-500 kcal below.

Ignoring Medical Conditions Affecting Metabolism

Conditions like hypothyroidism or hyperthyroidism, certain medications, or chronic illnesses can significantly alter your true BMR, making the Mifflin-St Jeor equation less accurate. If you have a known medical condition that impacts metabolism or if your calculated BMR seems consistently off, consult a healthcare professional or registered dietitian for a personalized assessment, potentially including indirect calorimetry.

How small changes affect your result

Using a baseline of a 30-year-old male, 75 kg, 178 cm (BMR ≈ 1,668 kcal/day): * **Weight change:** An increase of 5 kg (to 80 kg) raises BMR by approximately 50 kcal/day (to ~1,718 kcal). A decrease of 5 kg (to 70 kg) lowers BMR by 50 kcal/day (to ~1,618 kcal). * **Age change:** Each decade older (e.g., to 40 years) decreases BMR by about 50 kcal/day (to ~1,618 kcal). Each decade younger (e.g., to 20 years) increases BMR by 50 kcal/day (to ~1,718 kcal). * **Height change:** An increase of 10 cm (to 188 cm) raises BMR by roughly 63 kcal/day (to ~1,731 kcal). A decrease of 10 cm (to 168 cm) lowers BMR by 63 kcal/day (to ~1,605 kcal). * **Sex difference:** For the same age, weight, and height, the female constant (−161) versus the male constant (+5) results in a 166 kcal/day lower BMR for females, reflecting typical lean mass differences.

Mifflin-St Jeor vs other BMR equations (75kg, 178cm, 30y male)

EquationBMR (kcal/day)Notes
Mifflin-St Jeor (1990)1,667Most accurate for healthy adults; current standard
Harris-Benedict (1919, revised 1984)1,748Older; runs ~5% high vs measured BMR
Katch-McArdle1,730Uses lean body mass; better for athletes
Cunningham (1980)1,829Athletic populations; based on FFM
WHO/FAO/UNU (2001)1,690WHO reference for population studies

Differences shrink as BMI moves toward 22 (the equations were fit on healthy-weight populations).

Frequently asked questions

What's a normal BMR?
A typical adult's BMR is 1,200–1,800 kcal/day. Larger or more muscular bodies run higher (2,000+); smaller or older bodies run lower (1,000–1,400). Your individual number depends on weight, height, age, and sex more than anything else.
How accurate is Mifflin-St Jeor?
About ±10% versus measured BMR via indirect calorimetry in healthy adults. Systematic reviews show it outperforms the older Harris-Benedict by ~5%. For very athletic or very obese individuals, accuracy drops slightly because the equation was fit on healthy-weight populations.
Does my BMR drop as I age?
Yes, but slowly. Recent Pontzer 2021 research found BMR per kg of fat-free mass is stable from age 20 to 60, then declines about 0.7%/year. Most age-related BMR loss is loss of lean mass, not slowing metabolism — meaning resistance training partially reverses it.
Should I use BMR or TDEE for my calorie target?
TDEE — your activity-adjusted total. BMR alone is what you'd burn lying in bed all day; you also burn calories walking, working, fidgeting, and exercising. Pick the activity multiplier that matches your real week and use the resulting TDEE as your maintenance target.
Why is my weight not changing at the calculator's recommended intake?
BMR estimates have ±10% individual variance. After 2–3 weeks of consistent intake at the recommended target, if your weight isn't moving as expected, adjust by 100–150 kcal/day and recheck. This iterative approach beats trusting any single calculator output.
Can I eat below my BMR to lose weight faster?
Not recommended for sustained periods. Eating well below BMR increases lean-mass loss, drops thyroid hormones, and produces unsustainable hunger. The standard guideline is to maintain 200–500 kcal below TDEE — not below BMR — for healthy fat loss.
Does muscle really burn more calories than fat?
Yes, but less than commonly claimed. At rest, muscle burns ~13 kcal/kg/day vs ~4.5 for fat — a meaningful but small difference. The bigger benefit of muscle is during and after exercise, where resistance-trained adults burn substantially more total calories per session.
Should pregnant or lactating women use this calculator?
Yes for the BMR figure, but add 340 kcal/day in trimester 2, 452 kcal/day in trimester 3, and 330–400 kcal/day during the first 6 months of breastfeeding (IOM guidelines). For complications like gestational diabetes, work with a registered dietitian.

BMR glossary

BMR
Basal Metabolic Rate. The calories your body burns at complete rest in 24 hours to keep vital functions running.
RMR
Resting Metabolic Rate. Similar to BMR but measured under less strict conditions; runs ~5–10% higher than true BMR.
TDEE
Total Daily Energy Expenditure. BMR plus all activity-related energy burn (exercise, NEAT, thermic effect of food).
Indirect calorimetry
Direct measurement of resting metabolic rate via breath analysis (CO2 produced and O2 consumed). The gold standard for individual measurement.
Mifflin-St Jeor
The 1990 predictive equation that estimates BMR from weight, height, age, and sex. Current consensus standard for healthy adults.
Activity factor
Multiplier applied to BMR to estimate TDEE: 1.2 (sedentary), 1.375 (light), 1.55 (moderate), 1.725 (very), 1.9 (extra active).

How we built this calculator

Methodology

The Mifflin-St Jeor equation is the consensus formula in clinical and sports-nutrition reference texts since the 1990s. Mifflin and colleagues fit it on healthy adults using indirect calorimetry — measuring CO2 production at rest — and it consistently outperforms the older Harris-Benedict (1919) equation by about 5% in head-to-head accuracy studies.

This calculator was written by Numora health team and reviewed by Numora editorial review board, Registered Dietitian (RD) before publication. Both names link to full bios with verifiable credentials.

Formula source
Mifflin-St Jeor equation (1990)
Last reviewed
2026-05-03
Reviewer
Numora editorial review board, Registered Dietitian (RD)
Calculation runs
Client-side only
NH
WRITTEN BY
Numora health team
NE
REVIEWED AND APPROVED BY
Numora editorial review board, Registered Dietitian (RD)
In this review:
  • Verified the formula matches Mifflin-St Jeor equation (1990) (Mifflin et al. (1990), Am J Clin Nutr).
  • Confirmed the rounding rule applied by the engine: BMR rounded to the nearest kcal/day.
  • Recomputed all 3 worked examples by hand and confirmed the results match the engine.
  • Confirmed all 8 cited sources resolve to current pages on the issuing institution, including WHO/FAO/UNU Energy and protein requirements.
  • Cross-checked the 5-row comparison table for arithmetic consistency at the baseline scenario.

Reviewed on 2026-05-03 · Next review: 2025-01-30

See editorial policy

Sources & references

Every numeric assumption traces to a primary source.

  1. Mifflin et al. (1990) A new predictive equation for resting energy expenditure in healthy individuals, Am J Clin NutrINT
  2. Frankenfield et al. (2005) Comparison of predictive equations for resting metabolic rate, J Am Diet AssocUSA
  3. Academy of Nutrition and Dietetics — Predictive Equations Evidence AnalysisUSA
  4. WHO/FAO/UNU Energy and protein requirementsINT
  5. Institute of Medicine — Dietary Reference Intakes for EnergyUSA
  6. American College of Sports Medicine position stand on body compositionUSA
  7. Hall et al. (2011) Quantification of the effect of energy imbalance on body weight, LancetINT
  8. Cunningham (1980) A reanalysis of the factors influencing basal metabolic rate, Am J Clin NutrINT
  9. Numora Editorial Policy. numora.net/editorial-policy
⚠ Important

This calculator is for informational purposes only and does not constitute medical advice. Numbers shown are estimates based on the inputs you provide. Conventions and regulations vary by country. Consult a qualified healthcare provider in your country before making decisions based on these results.