Calculating basal metabolic rate: simple formula, examples, and calories per day

Basal metabolic rate calculation : estimate the minimum energy (kcal/day) your body expends at complete rest, then convert it into maintenance calories according to your activity.

• obtain a clear value in kcal/day (BMR)
• easily transition to the actual need (TDEE = maintenance)
• Define a deficit or surplus without starving yourself
• avoid common mistakes (formula, activity, objective)
• better understand what influences your energy expenditure (muscle, sleep, stress)

In practical terms: your basal metabolic rate (BMR) is not your total "calorie budget". It's the base, to which your activity level (and sometimes the thermic effect of food) is added to obtain your maintenance calories.

1) Basal metabolic rate (BMR) vs. maintenance calories (TDEE): do not confuse them

BMR = calories burned if you remained lying down for 24 hours, fasting, in a neutral environment (measured in a laboratory). In practice, it is estimated using a formula.

TDEE (Total Daily Energy Expenditure) = BMR × activity factor (a useful approximation of “maintenance”). This is the figure used to determine weight loss, maintenance, or gain.

What this changes: if you eat “your BMR”, you often create a deficit that is too large, difficult to maintain, and sometimes counterproductive.

2) The best formula for calculating basal metabolic rate (the most commonly used)

For most adults, the Mifflin-St Jeor is the most common reference in clinical nutrition for estimating BMR.

Mifflin-St Jeor formula

Male : BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5

Woman : BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161

Note: these equations are estimates. Individual variations exist (muscle mass, genetics, hormones, sleep, etc.).

3) Step-by-step calculation (simplest method)

In practice, do it in 4 steps:

• Step 1 : Note down weight, height, age, sex.
• Step 2 : Calculate the BMR with Mifflin.
• Step 3 : Choose an activity factor (table below).
• Step 4 : TDEE = BMR × activity. Adjust according to your objective.

4) Table: Activity factors for transitioning from BMR to TDEE

Practical tip: if you're unsure, choose the lower level. You can then adjust based on changes in weight/measurements over 2–3 weeks.

5) Concrete examples of calculation (BMR then maintenance)

Example 1 (woman)

Woman, 35 years old, 70 kg, 165 cm.

BMR = 10×70 + 6.25×165 − 5×35 − 161 = 700 + 1031.25 − 175 − 161 = 1395 kcal/d (approx.).

If activity “moderate” (1.55): TDEE ≈ 1395 × 1.55 = 2162 kcal/day .

What this changes: for gradual weight loss, you can aim for -300 to -500 kcal/day (e.g., 1660 to 1860 kcal/day) depending on hunger, sleep and activity.

Example 2 (man)

Male, 28 years old, 82 kg, 180 cm.

BMR = 10×82 + 6.25×180 − 5×28 + 5 = 820 + 1125 − 140 + 5 = 1810 kcal/d (approx.).

If slightly active (1.375): TDEE ≈ 1810 × 1.375 = 2489 kcal/day .

6) How to use your result according to the objective (loss, maintenance, gain)

1) Maintenance : eat close to the TDEE. Adjust ±100–200 kcal according to the trend (weight, waist circumference, energy).

2) Weight loss : moderate deficit (often 10–20% of TDEE). In practice: -300 to -500 kcal/day for many people.

3) Weight gain / mass : moderate surplus (+200 to +300 kcal/day), with sufficient resistance training and protein.

Tip: If you're aiming for sustainable weight loss, link your strategy to a broader framework (diet, stress, sleep). You can explore helpful resources: weight loss , stress and anxiety , sleep .

7) What really influences basal metabolism (and what you can improve)

• Lean mass (muscle) : the more lean mass you have, the higher your BMR. Muscle strengthening is a concrete lever for this.
• ge : BMR tends to decrease with age, especially if muscle mass decreases.
• Weight/height : the taller and heavier you are, the higher the BMR (simply because there is more tissue to "maintain").
• Sleep : insufficient sleep disrupts appetite and energy regulation (it's not just a matter of willpower).
• Chronic stress : can increase snacking, reduce spontaneous activity (NEAT) and complicate adherence.

For daily “invisible” activity (NEAT: walking, stairs, moving), you can also read: fatigue and energy .

8) Plants, nutrition and supplements: what helps (without unrealistic promises)

There is no "magic" plant that significantly and permanently increases BMR. However, certain approaches can help indirectly: improved satiety, increased energy, and better regularity.

• Proteins : promote satiety and support lean mass (useful in a deficit).
• Fiber : improves satiety and digestive regularity.
• Tea/caffeine : modest and variable effect, caution for anxious people and those who sleep.
• Stress management : an underestimated lever for sticking to a diet plan (see well-being ).

If you use supplements, check for tolerance, interactions, and quality. If you have a medical condition, are pregnant, or are undergoing treatment, seek professional advice.

9) Common mistakes (and how to avoid them)

• Using BMR for maintenance : maintenance = TDEE, not BMR.
• Overestimating activity : many people classify themselves as “moderately active” when they are actually “slightly active”.
• Changing too quickly : adjust after 14–21 days, not after 3 days.
• Too aggressive a deficit : hunger, fatigue, decreased performance → more likely to give up.
• Forget about NEAT : 2,000 steps vs 10,000 steps often makes more of a difference than “a fat burner”.
• Ignoring sleep : if you sleep poorly, the most “perfect” strategy on paper rarely holds up.

10) For whom is it useful (and when to seek medical advice)

Useful if :

• You want to lose weight without starving yourself
• you want to stabilize your weight
• You're getting back into sports and want to structure your training
• You want to understand why “I eat little but I don’t lose weight” (often a question of actual TDEE, monitoring or activity)

Seek medical/dietary advice if: history of eating disorders, pregnancy/breastfeeding, unstable hypothyroidism, chronic conditions, unintentional weight loss, significant unexplained fatigue.

11) Scientific references (to understand the limitations of the formulas)

Prediction equations like Mifflin-St Jeor are estimates and can vary depending on the profiles. They remain a practical and widely used tool.

To go further: scientific source (Mifflin-St Jeor), scientific source (Harris-Benedict, historical), scientific source (energy expenditure and components), scientific source (activity and expenditure, general public benchmarks).

FAQ — basic metabolism calculation

1) What is the best formula for basal metabolism?

For most adults, Mifflin-St Jeor is the most commonly used in practice for estimating BMR.

2) Why does my basal metabolic rate “decrease” when I lose weight?

Because your body is lighter (less tissue to support) and because you sometimes move less (lower NEAT). Hence the benefit of a moderate deficit and muscle strengthening.

3) Does sport significantly increase the basal metabolic rate?

Exercise primarily increases total energy expenditure (TDEE). BMR may increase slightly if you gain muscle mass.

4) Should I eat above my BMR?

The most logical approach is to think in terms of TDEE (maintenance). Sustainably eating below the BMR is often difficult and unnecessarily restrictive.

5) How can I tell if my TDEE is correct?

Monitor your intake and weight/waist circumference for 2–3 weeks. If it increases to the maintenance level, decrease by 100–200 kcal; if it decreases, increase by 100–200 kcal.

6) Do “fat burners” increase basal metabolic rate?

Their effect is generally modest, variable, and sometimes comes at the cost of undesirable effects (nervousness, sleeplessness). Priority: diet, activity, sleep, stress.

7) What deficit should I aim for to lose weight without fatigue?

Often 10–20% of TDEE (e.g., -300 to -500 kcal/day). Adjust according to hunger, performance, and sleep.

8) Does the calculation change if I am very muscular?

Yes, the formulas can underestimate the results in very muscular individuals. In this case, adjustment through actual monitoring (2–3 weeks) is essential.

Sources (list)

• Mifflin-St Jeor (PubMed)
• Harris-Benedict (PubMed)
• Components of energy expenditure (PubMed)
• Activity and calorie guidelines (Harvard Health)