The BMR calculator below estimates your Basal Metabolic Rate β the number of calories your body burns just to stay alive, with zero movement, over 24 hours. It runs your stats through three respected formulas at once, so you can see how they compare instead of relying on just one.
Arb Digital built this as a free, no-signup tool because BMR is the foundation almost every other calorie or diet calculation is built on top of. Get this number right and everything downstream β your TDEE, your macros, your deficit or surplus β gets more accurate too.
What This BMR Calculator Does
It calculates your Basal Metabolic Rate using three different, well-documented formulas β Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle β based on your weight, height, age, gender, and (for Katch-McArdle) your body fat percentage. It also shows a rough sedentary Total Daily Energy Expenditure by multiplying your selected BMR by 1.2, the standard activity multiplier for someone who gets little to no structured exercise.
How to Use It
- Choose your units. Toggle between imperial and metric β conversions happen automatically.
- Enter weight, height, and age. Use your current stats for the most accurate estimate.
- Select gender. Men and women have different average lean mass at the same weight, which the formulas account for.
- Pick a formula. Mifflin-St Jeor is the modern default; Harris-Benedict is the older classic; Katch-McArdle is most accurate if you know your body fat percentage.
- Enter body fat % if using Katch-McArdle. This field is ignored by the other two formulas.
- Read your results. The big number is your BMR under the selected formula; the grid compares all three plus a rough sedentary TDEE.
The Formulas Behind the Numbers
The Mifflin-St Jeor equation, published in 1990, is considered the modern standard. For men: BMR = 10 Γ weight(kg) + 6.25 Γ height(cm) β 5 Γ age + 5. For women, subtract 161 instead of adding 5. The Academy of Nutrition and Dietetics has found it more accurate than older equations across most body types, and it's the formula referenced by the USDA's Dietary Reference Intake calculator.
The Harris-Benedict equation, originally from 1919 and revised in 1984, was the standard for decades before Mifflin-St Jeor replaced it in most clinical settings. For men: BMR = 88.362 + 13.397 Γ weight(kg) + 4.799 Γ height(cm) β 5.677 Γ age. For women: BMR = 447.593 + 9.247 Γ weight(kg) + 3.098 Γ height(cm) β 4.330 Γ age. It tends to run slightly higher than Mifflin-St Jeor for many people, which is part of why it was largely superseded.
The Katch-McArdle formula takes a different approach entirely: instead of using total body weight, it calculates BMR from lean body mass alone β BMR = 370 + 21.6 Γ lean body mass(kg). Because it's based on lean mass rather than total weight, it tends to be the most accurate option for anyone who knows their body fat percentage, especially people who are notably leaner or more muscular than average, where weight-based formulas can over- or under-estimate.
BMR Is the Calories You'd Burn in a Coma
A useful way to think about BMR: it's roughly the number of calories your body would burn over 24 hours if you did absolutely nothing β no walking, no talking, no digesting food, just lying still and staying alive. Your heart still beats, your lungs still breathe, your brain still runs, your organs still function, and your body still regulates its temperature. All of that costs energy, and BMR is that cost.
For most people, BMR accounts for roughly 60-70% of total daily calorie burn β the single largest chunk of your energy expenditure, larger than exercise, larger than digestion, larger than daily movement combined. That's why getting your BMR estimate right matters so much: a small error here compounds into a much bigger error in your total daily calorie target.
Mifflin-St Jeor vs. Katch-McArdle: Which Should You Use?
For most people without a known body fat percentage, Mifflin-St Jeor is the better default β it's been validated across a broad, diverse population and doesn't require any extra data. But if you already know your body fat percentage from a DEXA scan, calipers, or a reasonably reliable smart scale, Katch-McArdle typically produces a more personalized number, because it's built directly from your lean body mass rather than an estimate based on average body composition for your weight, height, and age. Two people at the same weight and height can have meaningfully different BMRs if one carries much more muscle than the other β something only Katch-McArdle accounts for directly. You can estimate your lean mass first with our lean body mass calculator if you don't already know your body fat percentage.
Why BMR Falls With Age and With Weight Loss
BMR isn't fixed β it declines gradually with age, largely because lean muscle mass tends to decrease over the years unless it's actively maintained through resistance training. That's baked directly into the Mifflin-St Jeor and Harris-Benedict formulas, both of which subtract calories for every additional year of age. It's also why calorie needs at 50 are meaningfully lower than at 25, even at an identical weight, height, and activity level.
BMR also drops during sustained weight loss, and not just because there's less body mass to maintain. A phenomenon called adaptive thermogenesis means your body's metabolism slows down by somewhat more than body weight changes alone would predict β a survival mechanism that made sense during historical food scarcity but that makes long diets frustrating today. This is a major reason plateaus happen: the BMR you calculated at the start of a diet is higher than the BMR you actually have a few months in, so calorie targets often need to be recalculated periodically, not set once and left alone.
BMR is just the resting baseline β see your complete calorie and TDEE picture with activity factored in. Arb Digital builds fast, high-converting websites and content β explore our free tools while you're here.
Calorie & TDEE Calculator All Free ToolsWhy Three Formulas Instead of One
Showing all three results side by side, rather than just handing you a single number, is deliberate. Mifflin-St Jeor and Harris-Benedict were both built from population averages, and while Mifflin-St Jeor is the newer, more validated of the two, no weight-and-height formula can perfectly account for someone whose body composition sits far from average β a lifelong athlete, someone recovering from significant weight loss, or someone with a larger frame but low body fat. Seeing where Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle agree or disagree gives you a sense of how much confidence to put in the estimate. When all three land close together, you can trust the number more. When they spread out significantly, it's usually a signal that your body composition differs enough from population averages that a direct measurement β and the Katch-McArdle formula that uses it β deserves more weight than the other two.
What to Do With Your BMR Number
On its own, BMR isn't something you eat "at" β nobody should be targeting their BMR as a daily calorie goal, since that ignores all the energy you burn through actual movement and exercise. Instead, treat BMR as the floor you build on top of: multiply it by an activity factor to get your TDEE, then adjust that TDEE up or down depending on whether your goal is fat loss, muscle gain, or maintenance. Our calorie and TDEE calculator handles that next step directly, using the same underlying formulas as this page.
Common Mistakes to Avoid
- Confusing BMR with TDEE. BMR is your resting number only β it doesn't include activity, exercise, or digestion.
- Using Katch-McArdle with a guessed body fat %. A rough guess can throw the result off by more than a weight-based formula would be.
- Never recalculating. BMR changes as you age and as your weight changes β revisit it every few months, not just once.
- Eating below BMR long-term. Very low intakes can trigger stronger adaptive thermogenesis and are hard to sustain safely.
- Ignoring lean mass. Two people at the same weight can have different BMRs if their muscle mass differs significantly.
- Treating one formula's result as exact. All three are estimates; use the spread between them as a confidence check, not a contradiction.
Related Free Tools From Arb Digital
Add activity to this number with our TDEE calculator, set daily targets with our macro calculator, estimate your lean body mass for a more precise Katch-McArdle result, or compare against your ideal weight range. You can also check your body fat percentage. Browse our full free online tools hub for more.
Frequently Asked Questions
BMR, or Basal Metabolic Rate, is the number of calories your body burns at complete rest just to keep vital functions like breathing, circulation, and organ function running.
BMR is your resting baseline; TDEE (Total Daily Energy Expenditure) adds activity, exercise, and digestion on top of BMR to give your full daily calorie burn.
Mifflin-St Jeor is generally considered the most accurate for the general population; Katch-McArdle can be more accurate if you have a reliable body fat percentage.
Aging is typically associated with gradual loss of lean muscle mass, and muscle burns more calories at rest than fat, which lowers BMR over time.
Eating consistently below BMR isn't generally recommended without medical supervision, since it can be hard to sustain and may accelerate muscle loss and metabolic slowdown.
Yes β BMR typically decreases as body weight decreases, and can drop somewhat more than weight changes alone would predict due to adaptive thermogenesis.
This tool provides general estimates for educational purposes only and is not medical advice. Individual needs vary β consult a doctor or registered dietitian before making health, nutrition, or fitness decisions.
