What does your BMR result mean?
Your body is never truly “off.” Even at rest, it uses energy to breathe, circulate blood, maintain body temperature, support your brain and nervous system, and keep organs working. Your estimated BMR is the energy cost of that basic maintenance over a day.
It does not include walking to the kitchen, working, caring for children, training or digesting food. That is why treating BMR as “calories I should eat” gives the wrong answer.
| Number | What it includes | What to use it for |
|---|---|---|
| BMR | Basic functions under complete-rest conditions | Understanding your metabolic baseline |
| RMR/REE | Energy used while resting under less restrictive conditions | A practical clinical measure of resting needs |
| TDEE | BMR or RMR plus daily movement, exercise and digestion | Planning maintenance or weight-loss calories |
If you came here to decide how much to eat, take your result to the TDEE calculator. It adds the energy you use in real life and gives you a usable maintenance estimate.
How does the BMR calculator work?
The calculator uses the Mifflin-St Jeor equation by default. Mifflin and colleagues developed it from measured resting energy expenditure in healthy adults and published it in 1990. A later systematic review found it was the most reliable of the commonly used equations compared for healthy adults with and without obesity.
The equations use weight in kilograms, height in centimetres and age in years. The original research provided different constants for males and females, so the calculator asks for biological sex for the equation—not gender identity.
| Method | Exact formula |
|---|---|
| Mifflin-St Jeor, male | BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5 |
| Mifflin-St Jeor, female | BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161 |
| Lean body mass | Weight in kg × (1 − body-fat percentage ÷ 100) |
| Katch-McArdle option | BMR = 370 + (21.6 × lean body mass in kg) |
What does a worked BMR example look like?
For a 35-year-old woman who is 165 cm tall and weighs 75 kg, the female equation is 750 + 1,031.25 − 175 − 161. That produces 1,445.25 kcal/day, displayed as 1,445 kcal/day. It is still not an eating target because daily movement and digestion use additional energy.
Should you use Mifflin-St Jeor or Katch-McArdle?
For most people, choose Mifflin-St Jeor. It needs information you can measure reasonably well at home. If you have a professionally measured, current body-fat percentage, the lean-mass option commonly called Katch-McArdle may offer useful extra context.
Best default
Uses age, biological sex, height and weight. It cannot directly account for unusually high or low lean mass.
Body-composition option
Uses weight and body-fat percentage. A poor body-fat estimate produces a poor BMR estimate.
An honesty note: the second formula is widely labelled “Katch-McArdle” online, but its coefficients match the general resting-energy equation published by James Cunningham in 1991. The calculator keeps the familiar label while showing the equation in full.
How accurate is a BMR calculator?
It is a useful starting estimate, not a reading from inside your body. The ±10% context band makes uncertainty visible, but it is not a medical confidence interval and does not mean your true BMR must sit inside it.
For a measured resting metabolic rate, a trained professional can use indirect calorimetry, which estimates energy expenditure from respiratory gases. Even then, test conditions matter. For ordinary weight-loss planning, your weight trend over time is usually more actionable than chasing a perfectly measured resting number.
None of those differences is a character flaw or evidence of a “broken” metabolism. They are reasons to treat the result as a starting point and adjust with real-world evidence.
How do you turn BMR into a calorie target?
- Estimate BMR.Establish your resting baseline with the calculator above.
- Estimate TDEE.Add real activity with the TDEE calculator.
- Choose a deficit.Use the calorie deficit calculator to turn maintenance into a manageable starting target.
- Check the trend.Compare consistent intake with your weight trend over several weeks.
Read What is TDEE? for a plain-English explanation of how resting metabolism, movement, exercise and digestion fit together.
BMR calculator questions
What does BMR stand for?
BMR stands for basal metabolic rate: the energy your body uses to maintain essential functions at complete rest under tightly controlled conditions.
What is the difference between BMR and TDEE?
BMR covers basic survival functions at rest. TDEE includes BMR plus daily movement, planned exercise and digestion. BMR is the baseline; TDEE is the more useful estimate for deciding how much to eat.
Should I eat my BMR to lose weight?
Not as a general rule. BMR is not an intake recommendation and ignores the energy you use outside complete rest. Estimate TDEE first, then choose an appropriate deficit from that total.
Is BMR the same as resting metabolic rate?
Not exactly. BMR is defined under stricter laboratory conditions. Resting metabolic rate, also called resting energy expenditure, is measured under less restrictive conditions and may be slightly higher.
Which BMR formula is best?
Mifflin-St Jeor is the best default here because it performed well in a systematic review of common predictive equations and uses accessible inputs. If you know your body-fat percentage from a credible measurement, the lean-mass-based Katch-McArdle option can provide a useful comparison.
Does muscle increase BMR?
Fat-free mass is strongly related to resting energy expenditure, but more muscle does not produce the enormous calorie boost sometimes promised online. Strength training remains valuable for function and preserving muscle during weight loss.
Will my BMR fall as I lose weight?
Usually. A smaller body requires less energy, and the body can also adapt to a sustained energy deficit. Recalculate with your current weight, then check your TDEE and real weight trend.
Can I calculate BMR in stone and pounds?
Yes. Select stone, enter stone and pounds separately, and the calculator converts the value for the equation. You can switch among kilograms, pounds, and stone and pounds without changing the underlying result.
Why does the calculator ask for biological sex?
The original Mifflin-St Jeor equations use different fitted constants for males and females. The question is there only to select the published equation, not to ask about gender identity.