Result
- Sedentary TDEE (×1.2)desk job, minimal walking2,061 kcal/day
- Lightly active TDEE (×1.375)1-3 days/wk light exercise2,362 kcal/day
- Moderately active TDEE (×1.55)3-5 days/wk moderate exercise2,662 kcal/day
- Very active TDEE (×1.725)6-7 days/wk hard exercise2,963 kcal/day
- Extra active TDEE (×1.9)athlete or physical job3,263 kcal/day
How to use this calculator
- Pick a formula. Mifflin-St Jeor is the default and the most accurate for most adults.
- Enter sex, age, weight, and height. Choose Katch-McArdle only if you have a measured body fat % (DEXA, BodPod, or a calibrated bioimpedance scale).
- Read the BMR figure — that is your rest-only calorie need. The TDEE rows below show what you would need at various activity levels.
About this tool
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to keep its core processes running — heart, lungs, brain, body temperature, and cell maintenance. It accounts for roughly 60–75% of your total daily energy expenditure for a typical sedentary adult. BMR is not the same as TDEE (Total Daily Energy Expenditure): TDEE = BMR × an activity factor that adds movement, digestion, and exercise. Use BMR when you want the rest-only baseline; use TDEE when planning a calorie target for weight maintenance or change. The Mifflin-St Jeor equation (used here as the default) is the most accurate published BMR predictor for healthy non-obese adults, tracking measured resting energy expenditure within roughly 5% in validation studies.
What this calculator does
Estimates your Basal Metabolic Rate — the calories your body burns at complete rest — using the formula you select. Mifflin-St Jeor is recommended for most adults; Harris-Benedict (revised) is shown for comparison and historical reference ranges; Katch-McArdle uses lean body mass when you have a measured body fat percentage.
How it works — the formula
Mifflin-St Jeor (1990):
Men: 10·W(kg) + 6.25·H(cm) − 5·A(yr) + 5
Women: 10·W(kg) + 6.25·H(cm) − 5·A(yr) − 161
Harris-Benedict (Roza-Shizgal 1984 revision):
Men: 88.362 + 13.397·W + 4.799·H − 5.677·A
Women: 447.593 + 9.247·W + 3.098·H − 4.330·A
Katch-McArdle:
BMR = 370 + 21.6 · LBM(kg), where LBM = W · (1 − BF%/100)All three formulas predict resting energy expenditure in kcal/day. Mifflin-St Jeor is the modern default — derived on a broader, heavier sample than Harris-Benedict and validated to within ±5% in over half of healthy adults. The Harris-Benedict revision adjusts the 1919 original to fit late-20th-century population norms but still tends to over-predict BMR by 3-5%. Katch-McArdle replaces the height/sex/age proxies with direct lean-body-mass and is preferred when an accurate body fat % is available (DEXA or similar).
Worked examples
- Inputs:
- formula = Mifflin-St Jeor, sex = male, age = 30, weight = 75 kg, height = 178 cm
- Output:
- 10·75 + 6.25·178 − 5·30 + 5 = 750 + 1,112.5 − 150 + 5 ≈ 1,718 kcal/day
Multiply by 1.55 for a moderately active TDEE ≈ 2,663 kcal/day.
- Inputs:
- formula = Mifflin-St Jeor, sex = female, age = 40, weight = 65 kg, height = 165 cm
- Output:
- 10·65 + 6.25·165 − 5·40 − 161 = 650 + 1,031.25 − 200 − 161 ≈ 1,320 kcal/day
Sedentary TDEE ≈ 1,320 × 1.2 = 1,584 kcal/day; a 500-kcal deficit puts maintenance below 1,100 — too low. Add walking instead of cutting further.
- Inputs:
- formula = Katch-McArdle, weight = 80 kg, body fat = 15%
- Output:
- LBM = 80 · 0.85 = 68 kg; BMR = 370 + 21.6·68 ≈ 1,839 kcal/day
For an athlete training 6 days/week, multiply by 1.725 → TDEE ≈ 3,172 kcal/day.
What BMR measures
Basal Metabolic Rate (BMR) is the amount of energy your body uses at complete rest to keep the basic biological machinery running — heartbeat, breathing, cell maintenance, temperature regulation, kidney and liver function. It is the largest component of daily calorie expenditure, typically 60-75% of total daily energy needs for most people.
BMR is measured by indirect calorimetry (measuring oxygen consumption and carbon dioxide production during complete rest, ideally after a 10-12 hour fast). Because this measurement requires specialised equipment, most people estimate BMR using validated predictive equations. This calculator uses the Mifflin-St Jeor (1990) formula, the current clinical standard.
BMR is often confused with Resting Metabolic Rate (RMR) or Resting Energy Expenditure (REE). Technically BMR is measured immediately upon waking after 8 hours of sleep and 12 hours of fasting; RMR is a less-strict version measured after rest but without the sleep/fasting requirements. RMR is typically 5-10% higher than true BMR because of the small metabolic effects of prior food and activity. In everyday use the terms are used interchangeably.
The main BMR formulas
Three widely-cited formulas estimate BMR from height, weight, age, and sex:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161For a 30-year-old, 70 kg, 175 cm man: BMR = 10 × 70 + 6.25 × 175 − 5 × 30 + 5 = 700 + 1094 − 150 + 5 = 1,649 kcal/day. Mifflin-St Jeor is validated against modern populations and is preferred over the older Harris-Benedict formula.
Men: BMR = 88.362 + (13.397 × weight) + (4.799 × height) − (5.677 × age)
Women: BMR = 447.593 + (9.247 × weight) + (3.098 × height) − (4.330 × age)The historical BMR formula, updated in 1984 from the original 1919 version. Tends to overestimate BMR by 5-10% for modern populations because the original data came from a lean early-20th-century sample.
BMR = 370 + (21.6 × lean body mass in kg)Uses lean body mass instead of total weight. More accurate for very muscular or very obese individuals where total-weight-based formulas over- or under-estimate. Requires prior body-fat measurement.
BMR to TDEE — activity multipliers
BMR is only the resting portion of daily energy expenditure. Total Daily Energy Expenditure (TDEE) — computed by the Calorie Calculator — includes energy burned through movement (physical activity) and the thermic effect of food (energy used to digest and store nutrients). TDEE is what you actually need to maintain body weight.
The standard method for estimating TDEE from BMR is to multiply by an activity factor:
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little/no exercise | × 1.2 |
| Lightly active | Light exercise 1-3 days/week | × 1.375 |
| Moderately active | Moderate exercise 3-5 days/week | × 1.55 |
| Very active | Hard exercise 6-7 days/week | × 1.725 |
| Extra active | Physical job + hard daily exercise | × 1.9 |
Why BMR drops with age (and how to slow it)
BMR typically declines about 1-2% per decade in adulthood, driven primarily by loss of lean body mass. Skeletal muscle is metabolically active tissue — it burns roughly 6-10 kcal per pound of muscle per day at rest, versus 2 kcal per pound of fat. Losing 5-10 pounds of muscle per decade (typical without resistance training) drops daily BMR by 30-100 kcal.
Resistance training preserves and even builds muscle into old age, largely preventing this BMR decline. Studies of adults 60-90 following progressive strength programs show BMR maintained or increased. Adequate protein intake (0.7-1.0 g per pound of lean body mass daily) supports muscle preservation during this training.
Diet-induced weight loss also lowers BMR proportionally as body mass drops, and by an additional "adaptive thermogenesis" effect where the body downregulates metabolic rate during caloric restriction. This is why crash diets produce unsustainable results — the metabolic rate at the new lower weight is significantly lower than the linear prediction, making maintenance harder.
BMR variability between individuals
BMR estimation formulas capture only ~70% of the variance in actual measured BMR between individuals. The remaining 30% comes from genetic differences, thyroid function, medication effects, and body composition details not captured by height/weight/age/sex.
Thyroid function has a large effect. Hypothyroidism can lower BMR by 15-40%; hyperthyroidism can raise it by 25-50%. If your measured or perceived metabolism seems dramatically inconsistent with formula predictions, thyroid testing is a reasonable clinical step.
Genetic variation in mitochondrial efficiency, uncoupling proteins, and neuroendocrine set-point regulation produce BMR variation of 100-300 kcal/day between individuals of otherwise identical body composition. This is the "some people just seem to burn more" phenomenon, and it is real but modest — not enough to explain large weight differences between people with similar diets and activity.
Practical use of BMR for weight management
For weight loss: subtract 500 kcal from TDEE for approximately 1 lb/week fat loss (a 3,500 kcal deficit per week). More aggressive deficits (750-1,000 kcal/day) speed loss but risk muscle loss, metabolic adaptation, and unsustainability. For most people, 500 kcal/day is the sustainable maximum for long-term work.
For weight gain (muscle building): add 250-500 kcal to TDEE, combined with a resistance-training program and adequate protein intake. Faster gains typically produce more fat gain per pound of muscle. Genetic ceiling on muscle-building rate is roughly 0.5-2 lb of muscle per month for men and 0.25-1 lb per month for women, depending on training experience.
For maintenance: eat approximately TDEE. Track weight over 2-4 week windows rather than day-to-day — daily weight fluctuates 2-5 lb from water and gut content changes even at perfect energy balance.
These are starting points. Actual TDEE deviates from the formula prediction by ±15% for most people. Adjust intake based on 4-week weight trend, not initial calculation.
When to use this vs other tools
BMR is the rest-only baseline. If you actually want a daily calorie target, pick TDEE or one of the goal-aware tools below.
- Calorie Calculator (TDEE)
You want a daily calorie target that accounts for activity — TDEE = BMR × activity factor.
- Macro Calculator
You already know your calorie target and need to split it into protein, carbs, and fat.
- Protein Calculator
You only need a daily protein target by body weight and training goal.
- Lean Body Mass Calculator
You need an estimate of LBM to feed into the Katch-McArdle formula or to track body recomposition.
Authority note
Mifflin-St Jeor remains the formula endorsed by the Academy of Nutrition and Dietetics evidence-analysis review (Frankenfield 2005) as most accurate for healthy non-obese adults; the calculator defaults to it for that reason.
Limitations
- BMR equations were calibrated on healthy adults aged ~19–78. Pregnancy, lactation, hyperthyroidism, hypothyroidism, fever, and post-surgical states all shift true resting expenditure outside the predicted range.
- Predictions degrade in extremes of body composition. In adults with BMI > 40, Mifflin-St Jeor tends to over-predict; in very lean athletes, Katch-McArdle is the better choice if a real body fat measurement is available.
- BMR is not RMR. Resting Metabolic Rate (RMR) is measured under less strict conditions than BMR and runs about 10% higher; most modern equations (Mifflin-St Jeor included) are technically RMR predictors despite the BMR label.
- These equations cannot detect adaptive thermogenesis after sustained dieting, which can suppress real BMR 5–15% below the predicted figure for months after weight loss.
For general planning and educational use only. This calculator does not provide medical, nutrition, or weight-management advice. Consult a registered dietitian or physician before basing a clinical intervention on these numbers.