BMR Calculator: Basal Metabolic Rate & TDEE

The Mifflin-St Jeor Equation, Term by Term

Variables Explained

What Moves Your BMR Up or Down

• 1Worked example: a 35-year-old man, 80 kg and 178 cm → 10×80 + 6.25×178 − 5×35 + 5 = 1,742.5 kcal/day before any activity is counted.
• 2Your organs quietly burn most of your daily calories: the liver and brain together consume close to half of your resting energy, even while you sleep.
• 3BMR naturally declines about 1-2% per decade after your twenties, mostly because of lost muscle. Resistance training can slow that decline and keeps your resting burn higher over the years.
• 4Crash diets that severely restrict calories can lower your BMR by 10-20% as your body enters conservation mode. This is one reason why rapid weight loss is often followed by rapid regain.
• 5Two people with matching stats — same height, weight, age, and sex — can still differ by 200 or more calories in BMR, because genetics, thyroid function, and lean mass all shift the baseline. Validate the estimate against two weeks of real scale data.
• 6Your BMR is the calorie floor your body needs just to exist, so it is not a weight-loss target to undercut. Pair any calorie goal with your real measured or calculated BMR rather than an arbitrary number.

Metabolism Terms You Should Know

BMR

Basal Metabolic Rate — the energy spent keeping your organs running, measured under strict lab conditions: awake, fasted, lying still, at neutral room temperature.

TDEE

Total Daily Energy Expenditure — BMR plus the thermic effect of food plus every movement you make, from workouts down to fidgeting.

Thermic Effect of Food (TEF)

The digestion overhead of a meal — roughly 10% of daily burn, with protein costing two to three times more energy to process than fat.

Activity Factor

A multiplier applied to BMR to estimate TDEE based on daily physical activity level, ranging from 1.2 (sedentary) to 1.9 (very active).

Research Papers & Institutes

Our calculations are based on established financial and scientific formulas. The following sources inform the default values and methodology used in this calculator:

• Mifflin MD, St Jeor ST, et al. — The 1990 resting metabolic rate prediction equation in wide clinical use
• National Institutes of Health (NIH) — Body Weight Planner, an energy-balance simulation model
• Academy of Nutrition and Dietetics — Evidence-based guidance on calorie needs

BMR vs TDEE: What's the Difference?

BMR (Basal Metabolic Rate) is the calories your body burns at complete rest to maintain vital functions like breathing and cell production. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for daily movement and exercise. TDEE is always higher than BMR — typically 1.2 to 1.9 times BMR depending on activity level.

Activity Multipliers

Worked Example

A 30-year-old male, 175 cm tall, weighing 75 kg, exercising 4 times per week:
• BMR = 10×75 + 6.25×175 - 5×30 + 5 = 1,724 kcal
• Activity multiplier (moderate) = 1.55
• TDEE = 1,724 × 1.55 = 2,672 kcal
• For weight loss: 2,672 - 500 = 2,172 kcal/day
• For muscle gain: 2,672 + 300 = 2,972 kcal/day

Use BMR to understand your metabolic baseline, but always use TDEE for setting daily calorie targets. Eating below BMR is not recommended as it can slow metabolism and cause muscle loss.

BMR Estimation Methods: Mifflin-St Jeor vs Harris-Benedict

Several formulas exist for estimating BMR, with the Mifflin-St Jeor equation (1990) being the most accurate for the general population. The older Harris-Benedict formula (1919) tends to overestimate BMR by 5-10%. Here is how they compare across different body types.

For most people, the Mifflin-St Jeor equation (used in this calculator) provides the most reliable BMR estimate without needing body composition data. If you know your body fat percentage, the Katch-McArdle formula can be more accurate. Use BMR as a baseline — always base your actual calorie targets on TDEE, not BMR.

Related Calculators