CodeKitHubWhat Is This Tool?
Basal metabolic rate (BMR) is the energy your body uses per day at complete physical and digestive rest — the cost of keeping you alive: breathing, circulation, cell repair, brain function. For most people it accounts for 60–75% of all calories burned in a day, which makes it the foundation of any calorie calculation.
Because measuring BMR directly requires laboratory conditions (indirect calorimetry after an overnight fast), everyday practice relies on prediction formulas. This calculator shows the two most established ones. Mifflin-St Jeor, published in 1990, was derived from modern populations and is what the Academy of Nutrition and Dietetics recommends. Harris-Benedict dates from 1919 (revised in 1984) and tends to produce slightly higher numbers — typically by around 5% — because it was built on leaner, more active early-20th-century subjects. Seeing both tells you the realistic range your true BMR probably falls in.
Why Use It?
- Shows Mifflin-St Jeor and Harris-Benedict results side by side, so you see the plausible range instead of a single false-precision number.
- Explains the difference between the formulas and which one modern dietitians prefer.
- Supports metric (cm, kg) and imperial (feet/inches, pounds) units.
- BMR is the foundation for daily calorie planning — pair it with an activity factor to get your full daily needs.
- Free and instant, with nothing uploaded — the calculation runs entirely in your browser.
How to Use
- Select your sex and enter your age.
- Enter your height and weight, in metric or imperial units.
- Press the calculate button.
- Read your BMR from both formulas, in calories per day.
Example
Input
Female, 28 years, 165 cm, 60 kgOutput
Mifflin-St Jeor ≈ 1,330 kcal/day — Harris-Benedict ≈ 1,400 kcal/dayMifflin-St Jeor: 10×60 + 6.25×165 − 5×28 − 161 = 1,330 kcal. The revised Harris-Benedict gives about 1,400 kcal — roughly 5% higher, a typical gap between the two formulas.
Mifflin-St Jeor vs Harris-Benedict at a glance
| Mifflin-St Jeor | Harris-Benedict (revised) | |
|---|---|---|
| Published | 1990 | 1919, revised 1984 |
| Derived from | Modern adult population | Early-20th-century subjects |
| Typical result | Baseline | About 5% higher |
| Recommended by | Academy of Nutrition and Dietetics | Still common in older literature and apps |
What BMR does and doesn't include
- Included: breathing, heartbeat, brain activity, cell repair, maintaining body temperature — the energy cost of simply being alive at rest.
- Not included: any movement (even standing or fidgeting), digestion of food, and exercise. Those are added on top when calculating total daily needs.
- BMR falls with age (roughly 1–2% per decade after 20) and rises with muscle mass — two people of identical weight can differ by hundreds of calories.
- These formulas are estimates for generally healthy adults. They are not designed for pregnant women, children, teenagers or people with thyroid or metabolic conditions — for those situations, consult a doctor rather than a formula.
- This tool is for general reference only and is not a substitute for professional medical advice, diagnosis or treatment.
From BMR to a daily eating plan
BMR on its own answers 'what does my body burn at rest' — it is not the number you should eat. To turn it into a daily target, multiply by an activity factor and, if you have a goal, add or subtract a sensible margin. The Calorie Calculator does exactly that on top of the same Mifflin-St Jeor formula.
For a fuller picture of body composition alongside metabolism, the Body Fat Calculator estimates body-fat percentage from tape measurements, the BMI Calculator gives a quick weight-for-height screening, and the Water Intake Calculator covers daily hydration.
→ Calorie Calculator · Body Fat Calculator · BMI Calculator · Water Intake Calculator
Frequently Asked Questions
What is the Mifflin-St Jeor formula?
For men: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5. For women: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161. Published in 1990, it was derived from measurements of modern adults and validation studies have found it the most accurate common formula, which is why it is the default recommendation today.
What is the Harris-Benedict formula?
The revised (1984) version used here is, for men: BMR = 13.397×weight + 4.799×height − 5.677×age + 88.362; for women: BMR = 9.247×weight + 3.098×height − 4.330×age + 447.593. It is the oldest widely used BMR equation and typically estimates around 5% higher than Mifflin-St Jeor.
Why do the two formulas give different results?
They were fitted to different populations decades apart. Harris-Benedict was derived in 1919 from relatively lean, active subjects; Mifflin-St Jeor was derived in 1990 from a broader modern sample. Neither is 'wrong' — the gap between them (usually 50–150 kcal) is a good reminder that any formula is an estimate with an error margin of roughly ±10%.
What is the difference between BMR and daily calorie needs?
BMR only covers what you burn at complete rest. Your actual daily needs (TDEE) add everything else — walking, working, digesting food, exercising — by multiplying BMR by an activity factor between 1.2 and 1.9. If you want the 'how much should I eat' number, use a calorie/TDEE calculator built on top of BMR.
Can I raise my BMR?
Mostly through body composition: muscle tissue burns more energy at rest than fat tissue, so resistance training that adds muscle raises BMR over time. Crash dieting works in the opposite direction — large, prolonged calorie deficits can lower resting metabolism as the body adapts.
Is this medical advice, and is my data stored?
No on both counts. The results are general estimates, not medical advice — pregnant women, minors, older adults and people with medical conditions should consult a doctor or dietitian. The calculation runs entirely in your browser; nothing is sent to a server, stored or logged.