BMR Calculator
Basal metabolic rate — 3 formulas: Mifflin-St Jeor, Harris-Benedict, Katch-McArdle
BMR Calculator turns basal metabolic rate into an instant, step-by-step result. Fill in Formula and read your answer immediately. The calculation is displayed with all its working, so the number always makes sense. Great when you want certainty fast — no formulas to memorize, no apps to install. Your inputs never leave your device: the calculation is fully client-side, and optional analytics/advertising only activate with your consent. One of 1206+ free CalcProMaster calculators covering bmr calculator for women over 50, calorie burn calculator at rest and similar everyday questions. No learning curve: the fields are clearly labeled and the result explains itself. Give BMR Calculator a try — it takes seconds and costs nothing.
What does the BMR Calculator do?
BMR Calculator works out the bmr from the Weight, Height, and Age, following standard Health conventions — the page defaults produce a bmr of 1618 cal/day (Mifflin-St Jeor).
- Inputs: Weight, Height, and Age.
- Output: the bmr, plus the intermediate steps behind it.
- Method: the standard Health formula, evaluated entirely in your browser.
Quick answer
With the default inputs (weight of 70, height of 170, age of 30), bmr calculator returns a bmr of 1618 cal/day (Mifflin-St Jeor). Assumptions and limits are summarized below.
How does the BMR Calculator work?
BMR Calculator computes the bmr directly from your inputs — the Weight, Height, and Age feed the formula. Nothing is uploaded: the math runs locally in your browser and the result appears as you type.
What This Calculator Really Does
Your basal metabolic rate (BMR) is the energy your body spends keeping you alive at complete rest — breathing, circulation, cell repair, brain function — before any activity is counted. This calculator estimates it from the two formulas clinicians and dietitians actually cite: Mifflin-St Jeor (the current default in nutrition practice) and the older Harris-Benedict equation.
BMR is the foundation number behind calorie targets: add activity on top of it and you get TDEE (total daily energy expenditure), which is what weight plans are really built on. An honest BMR estimate therefore comes with an honest error bar — the formulas were derived from population studies, and individuals can sit well above or below the line.
Everything runs locally in your browser; nothing about your body is transmitted or stored.
Quick answer: a 35-year-old male, 175 cm, 75 kg has a Mifflin-St Jeor BMR of about 1,674 kcal/day — roughly 80% of the calories he burns in a sedentary day.
The Formulas, Explained Plainly
Mifflin-St Jeor: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5 (men) / −161 (women)
Revised Harris-Benedict: men: 88.362 + 13.397×W + 4.799×H − 5.677×A; women: 447.593 + 9.247×W + 3.098×H − 4.330×A
- Weight (W) — kilograms; the dominant term in both equations.
- Height (H) — centimetres, capturing body size beyond weight alone.
- Age (A) — years; BMR falls slowly with age in these models.
The two formulas can differ by about 5% for the same person. That spread is not an error — it is an honest picture of how precise any population-derived equation can be for one individual.
How to Use It — In Order
- Choose units — metric (kg/cm) or imperial, consistently.
- Enter sex, age, height, weight — the four inputs both formulas use.
- Read your BMR — the rest-day energy floor in kcal/day.
- Multiply by activity — 1.2 sedentary up to 1.9 very active gives TDEE, the number that actually governs weight change.
- Treat it as a starting point — track real-world weight trends for two to three weeks and adjust.
Worked Example, Verified by Hand
Man, 35 years, 175 cm, 75 kg — Mifflin-St Jeor:
- 10 × 75 = 750 (weight term).
- 6.25 × 175 = 1,093.75 (height term).
- 5 × 35 = 175 (age subtraction).
- 750 + 1,093.75 − 175 + 5 = 1,673.75 ≈ 1,674 kcal/day.
Sedentary TDEE: 1,674 × 1.2 ≈ 2,009 kcal/day. Moderately active (×1.55): ≈ 2,595 kcal/day. Those two numbers bracket where his maintenance calories actually sit.
Common Mistakes to Avoid
- Eating at BMR and wondering why you are exhausted — BMR excludes daily activity; plan around TDEE, not BMR.
- Using morning weight after a salty meal — weigh fasted, several days, and average.
- Assuming muscle vs fat makes no difference — lean mass raises real energy use above what the formula predicts.
- Applying athletic-body numbers to the equations — they were derived from general populations.
- Changing targets daily — give any plan two to three weeks before adjusting.
Limitations
- Population equations carry individual error commonly cited around ±10% or more.
- Very muscular, older, or clinical populations fall outside the derivation data.
- Illness, medication, sleep and stress shift real expenditure in ways no static formula captures.
- This is a fitness planning tool, not a medical assessment.
Expected Accuracy
Mifflin-St Jeor is the formula dietetics practice treats as the best general predictor, but any BMR equation is an estimate of a quantity best measured with calorimetry. Expect the true value for an individual to differ from the estimate — use trends, not the single number, to steer.
Privacy — Your Data Never Leaves This Device
Height, weight and age are computed locally and never transmitted. No account, no tracking, works offline after first load.
Related Tools & Guides
Natural next steps from BMR:
- All Health Calculators
- Calorie Calculator — TDEE with activity
- BMI Calculator
- Body Fat Calculator
- Macronutrient Calculator
Sources & Standards
Both formulas are published, peer-reviewed equations used across nutrition practice.
- NIH — energy expenditure research
- CDC — healthy weight resources
- Academy of Nutrition and Dietetics — evidence-based practice guidelines
Bottom Line
BMR is the floor, TDEE is the plan. Use this calculator to get an honest starting estimate, then let two to three weeks of real-world weight data — not the formula — make the final call.
From Our Guides Library
Frequently Asked Questions
What is BMR in simple terms?
The calories your body would burn in 24 hours if you did nothing but rest — the energy cost of staying alive.
Which formula is more accurate, Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor is generally considered the better general predictor and is the default in modern dietetics practice; the two usually agree within about 5%.
Should I eat at my BMR to lose weight?
No. BMR excludes daily activity. Deficits are set against TDEE (BMR × activity factor), and eating below BMR is neither required nor generally advisable.
Why do two calculators give me different BMRs?
Different formulas, derived from different study populations. A spread of up to 5% is normal — it reflects the real precision of any such equation.
Does muscle increase BMR?
Yes — lean tissue is metabolically active, so muscular individuals burn more than the formula predicts at the same weight.
Is BMR the same as RMR?
Not quite: RMR (resting metabolic rate) is measured under looser conditions and typically runs slightly higher than strict BMR.
How often should I recalculate?
After meaningful weight change (±5 kg), a big training shift, or each new decade of age.
Is this calculator free and private?
Yes — it runs in your browser, requires no sign-up, and never sends your data anywhere.
What does the BMR Calculator calculate?
BMR Calculator turns the values you enter into a verified figure — the formula, every intermediate step, and the assumptions sit beside the result instead of hidden behind it. Because the working is visible: BMR Calculator shows each operation behind the figure in the steps panel, so you can verify the result instead of trusting a black box.
How is the result calculated?
The first steps are formula (mifflin-st jeor, 1990):, then male: bmr = 10w + 6.25h - 5a + 5. BMR Calculator substitutes the Weight, Height, and Age into the formula, evaluates it in the order shown in the steps panel, and reports the bmr rounded for readability.
What do I need to use the BMR Calculator?
The Weight, Height, and Age it asks for, or the page defaults if you just want to see the calculation work. Each input maps directly to the formula, and changing any one of them recalculates the bmr instantly.
What does the result from the BMR Calculator mean?
The main number the bmr calculator returns is the bmr for your exact inputs, and the supporting figures and step list give it context. BMR Calculator assumes the units shown in each label — entering values in different units will skew the figure proportionally.
When is the BMR Calculator most useful?
Typical uses for BMR Calculator include planning around a target figure, comparing scenarios side by side, and double-checking a figure before acting on it — anywhere the figure needs to be defensible rather than guessed. Run BMR Calculator twice with deliberately low and high inputs; the spread tells you how sensitive the figure is, which a single run never shows.