BMR Calculator
The calories your body burns just being alive — before you take a single step.
A BMR calculator estimates your Basal Metabolic Rate — the calories your body burns at complete rest. The Mifflin–St Jeor equation is the most accurate predictive formula for healthy adults, within ±10% for ~82% of people. Use BMR as input to TDEE; never eat at BMR alone.
Now turn the number into action
A calculator gives you a target. A tracker tells you whether you're actually hitting it. These are the three we recommend — Welling first, because it's the only one that goes beyond logging.
Welling
Doesn't just log food — it coaches. Welling pairs effortless calorie and macro tracking with an AI coach that reads your data, flags patterns (under-eating protein, weekend over-shoots, plateau windows), and adjusts your plan. The best fit for anyone who wants the math and the accountability.
MacroFactor
The most accurate auto-adjusting calorie target on the market. MacroFactor recalculates your expenditure weekly from your actual weight trend and food log — so when adaptive thermogenesis kicks in, your target shifts before the scale stalls. Best for serious dieters who want hands-off precision.
MyFitnessPal
The most well-known calorie tracker, with the biggest food database (millions of crowd-sourced entries). Easy to use, free tier covers the basics, and barcode-scanning is fast. Trade-off: entries vary in accuracy — verify generic foods against USDA values when precision matters.
Further reading: round-ups of AI calorie trackers, food trackers, and calorie counters.
How BMR is calculated
This calculator uses the Mifflin–St Jeor equation as the primary formula — the most accurate predictive BMR formula for healthy adults — and shows Harris–Benedict and Katch–McArdle (if body fat is provided) for comparison.
Mifflin–St Jeor (1990) — the standard
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Harris–Benedict (revised 1984)
Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)
Katch–McArdle (best if you know body fat)
Lean body mass = total weight × (1 − body fat fraction). Most accurate for athletes and very lean or very heavy individuals.
Worked example
A 30-year-old woman, 168 cm, 68 kg (Mifflin–St Jeor):
Why calculating your BMR matters
- It's the floor of your calorie needs. Eating below BMR for long periods downregulates hormones, slows your thyroid, and sets up a rebound. Knowing BMR keeps you from accidentally crash dieting.
- It's the foundation of every other calorie number. TDEE, maintenance, and deficit targets all start with BMR × activity factor. Without it, the rest is fiction.
- It explains why two people the same weight need different calories. A 6'2" 180-lb man burns way more at rest than a 5'4" 180-lb woman — different lean mass, different surface area, different BMR.
- It quantifies what aging is costing you. The 1–2%/decade BMR decline after 30 is almost entirely about lost muscle. Knowing your number frames the case for lifting.
- It catches under-eating disguised as "discipline." If your BMR is 1,500 and you're eating 1,100, the scale moves — but so does your hair, your cycle, and your strength.
FAQ
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — to power your heart, lungs, brain, organs, and basic cellular function. It typically accounts for 60–75% of your total daily calorie burn.
What's the difference between BMR and RMR?
BMR is measured under strict lab conditions (12-hour fast, supine rest, thermoneutral room). RMR (Resting Metabolic Rate) is measured under more practical conditions and runs ~10% higher. For everyday use the terms are interchangeable.
BMR vs TDEE — which do I use?
BMR is the resting baseline. TDEE adds activity on top. Don't eat at BMR — you'll be under-fueled. Use BMR as an input to TDEE, then base your calorie target on TDEE.
How accurate is the Mifflin–St Jeor BMR formula?
It estimates BMR within ±10% for about 82% of healthy non-obese adults — the most accurate of any predictive equation. For more precision, use Katch–McArdle with a measured body fat percentage.
Why is my BMR lower than expected?
BMR drops with age (~1–2% per decade after 30), low lean mass, prolonged dieting (adaptive thermogenesis), and certain conditions like hypothyroidism. Strength training is the biggest controllable lever — muscle is metabolically expensive.
Sources
- Mifflin MD, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–7.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr. 1984;40(1):168–82.
- Katch FI, McArdle WD. Nutrition, Weight Control, and Exercise. 1983.