BMR Calculator
Find your basal metabolic rate using the Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle formula, then see your total daily calorie needs across every activity level.
What BMR actually measures
Basal metabolic rate is the number of calories your body burns in a full day doing absolutely nothing but staying alive — no walking, no talking, no digesting, not even sitting up. It covers the energy cost of breathing, circulating blood, regulating body temperature, and running your brain and nervous system, which together are surprisingly expensive processes even at complete rest. For most people, BMR accounts for somewhere between 60% and 75% of total daily calories burned, making it by far the largest single piece of your daily energy budget.
That's exactly why BMR is the starting point for almost every calorie-based fitness or nutrition plan. Once you know your baseline, adding your activity level on top gives you TDEE — your actual total daily calorie burn — which is the number that matters for setting a realistic weight loss, maintenance, or muscle-gain target.
The three BMR formulas, compared
Mifflin-St Jeor (1990)
10 × weight(kg) + 6.25 × height(cm) − 5 × age + s
Where s is +5 for men and −161 for women. Published in 1990 and validated against modern body composition data, this is generally considered the most accurate formula for the general population and is the default used in this calculator.
Harris-Benedict (Revised)
Men: 88.36 + 13.4w + 4.8h − 5.7a
First published in 1919 and revised in 1984, this was the standard BMR formula for most of the 20th century. It tends to run slightly higher than Mifflin-St Jeor for many people, which is why it's been gradually superseded in most modern tools.
Katch-McArdle
370 + 21.6 × lean body mass (kg)
Uses fat-free mass instead of total weight, since muscle burns more calories at rest than fat does. It's the most accurate option available here — but only when paired with a genuinely accurate body fat percentage.
Which one should you pick?
Use Mifflin-St Jeor by default. Switch to Katch-McArdle only if you have a reasonably trustworthy body fat percentage from a scale, calipers, or the body fat calculator — a rough guess will make Katch-McArdle less accurate than simply using Mifflin-St Jeor instead.
Worked example: 30-year-old man, 5'9", 170 lb
Converting to metric first: 170 lb ≈ 77.1 kg, and 5'9" ≈ 175.3 cm. Using the Mifflin-St Jeor formula for men:
10 × 77.1 + 6.25 × 175.3 − 5 × 30 + 5 = 771 + 1,095.6 − 150 + 5 ≈ 1,722 kcal/day
That's his BMR — the calories he'd burn lying still all day. Add a "lightly active" multiplier of 1.375 for someone who exercises a few times a week, and his estimated TDEE comes out to roughly 2,368 kcal/day — the number that actually reflects a normal day's total calorie burn, and the one that matters most for setting a calorie target.
BMR vs. TDEE vs. RMR — what's the difference?
| Term | What It Measures | Typical Value vs. BMR |
|---|---|---|
| BMR | Calories burned at complete rest, strict lab conditions | Baseline (100%) |
| RMR | Calories burned at rest under normal, less strict conditions | ~5-10% higher than BMR |
| TDEE | Total calories burned in a full day including all activity | ~130-190% of BMR, depending on activity level |
In practice, most online calculators (including this one) technically estimate something closer to RMR than laboratory-strict BMR, since the exact fasting, temperature, and rest conditions real BMR testing requires aren't practical outside a research setting. The difference is small enough that it doesn't meaningfully change how you'd use the number day to day.
What actually changes your BMR
- Muscle mass: more fat-free mass means a higher BMR, since muscle tissue is metabolically more active than fat tissue even at rest.
- Age: BMR tends to decline gradually through adulthood, largely tracking the natural loss of lean muscle mass over time.
- Sex: men typically have a higher BMR than women at the same weight, mainly due to a higher average proportion of fat-free mass.
- Body size: larger bodies generally have a higher BMR simply because there's more tissue to maintain.
- Genetics and hormones: thyroid hormone levels in particular have a direct, measurable effect on metabolic rate.
- Severe calorie restriction: very aggressive, prolonged dieting can lower BMR as the body adapts to conserve energy — part of why extreme diets often stall out over time.
Turn your BMR into a full picture
BMR on its own is just one input — the real value comes from combining it with the rest of your health numbers. If you haven't already checked your BMI calculator result, it's a quick companion metric that adds useful context to a weight-related goal, even though it measures something different from metabolic rate. And once you know your TDEE from this calculator, the calorie calculator is the natural next step for turning that number into an actual daily calorie target for weight loss, maintenance, or muscle gain.
If you want the most accurate BMR result this tool can give, using the Katch-McArdle formula with a real body fat percentage is the way to get there — and the body fat calculator is the fastest way to get a reasonable estimate of that number if you don't already have one from a scale or calipers.
BMR calculator — FAQ
What is BMR and why does it matter?
BMR, or basal metabolic rate, is the number of calories your body burns each day just to keep itself alive — breathing, circulating blood, regulating temperature, and running your brain and nervous system — if you did absolutely nothing else at all. It's the floor of your daily calorie needs, not your total needs, and it matters because it's the foundation every calorie target for weight loss, maintenance, or muscle gain is built on top of.
Which BMR formula is the most accurate?
The Mifflin-St Jeor equation, published in 1990, is generally considered the most accurate for the general population and is what most modern calculators default to, including this one. The older Harris-Benedict equation, first published in 1919 and later revised, tends to slightly overestimate BMR for many people. The Katch-McArdle formula is the most accurate option specifically when you know your body fat percentage, since it calculates BMR from lean body mass rather than total weight, removing fat mass from the equation entirely.
Why does Katch-McArdle need my body fat percentage?
Katch-McArdle calculates BMR based on fat-free mass alone, since muscle and organ tissue burn substantially more calories at rest than fat tissue does. Two people can weigh the exact same amount and have meaningfully different BMRs if one carries more muscle — Katch-McArdle is built to capture that difference directly, but it can only do so if you provide a reasonably accurate body fat percentage. Without a decent estimate, this formula's advantage over Mifflin-St Jeor disappears.
What's the difference between BMR and TDEE?
BMR is what you'd burn lying in bed all day doing nothing. TDEE, or total daily energy expenditure, adds everything else on top — the calories burned from walking, working, exercising, fidgeting, and even digesting food. TDEE is calculated by multiplying your BMR by an activity multiplier, and it's the number that actually reflects how many calories you burn in a normal day, which is why it's the more useful figure for setting a weight loss, maintenance, or muscle-gain calorie target.
What's the difference between BMR and RMR?
They're closely related but not identical. BMR is measured under very strict conditions — typically upon waking, after an overnight fast, in a thermoneutral environment, without having exercised. RMR, or resting metabolic rate, is measured under more relaxed real-world conditions and includes a small amount of energy used for digesting recent food, making it typically 5-10% higher than true BMR. In practice, most online calculators — including this one — technically estimate something closer to RMR, since true laboratory BMR conditions aren't practical to replicate at home.
Can I increase my BMR?
To a meaningful degree, yes. Building muscle through resistance training is the most reliable lever, since muscle tissue burns more calories at rest than fat tissue does — this is exactly why the Katch-McArdle formula weights fat-free mass so heavily. Age works against you here, since BMR tends to decline gradually over adulthood as lean mass naturally decreases, but strength training can meaningfully offset that decline. Severe, prolonged calorie restriction tends to lower BMR as the body adapts to conserve energy, which is one reason extremely aggressive diets often backfire over time.
Is a higher or lower BMR better?
Neither is inherently "better" — BMR is simply a description of your body's baseline energy needs, not a fitness score. A higher BMR means you can eat more calories while maintaining the same weight, which some people see as an advantage, but BMR itself isn't something to chase for its own sake. It's most useful as an input for calculating an appropriate calorie target for whatever your actual goal is, rather than a number to optimize directly.
This calculator is for educational purposes only. It is not medical advice. Always consult a qualified doctor or health professional before making health decisions.
