Resting Metabolic Rate Calculator

Your resting metabolic rate (RMR) accounts for 60–75% of the calories you burn each day – even before you lace up your sneakers. Understanding this number transforms vague calorie goals into a data‑backed plan. Whether you want to lose fat, build muscle, or simply maintain your weight, the right starting point is your RMR.

The calculator below estimates exactly how much energy your body needs at complete rest. Provide a few details, and you will have a personalized baseline in seconds.

[Provide your age, sex, weight, height, and body fat percentage (if known). The calculator will instantly estimate your RMR using the Mifflin‑St Jeor equation by default. For athletes or those with known lean body mass, switch to the Cunningham formula for greater precision.]

What Is Resting Metabolic Rate?

Resting metabolic rate is the number of calories your body burns to maintain essential functions while you are awake but inactive – breathing, circulating blood, repairing cells, and regulating temperature. It is measured under comfortable conditions, typically after a short rest, without the overnight fast required for basal metabolic rate (BMR).

RMR generally runs 5–10% higher than BMR because it includes the slight energy cost of digestion and daily wakefulness. For practical nutrition planning, RMR is the more useful number, and all major equations in this calculator estimate RMR, not the stricter BMR.

How the Calculator Estimates Your RMR

The tool applies two of the most respected formulas in metabolic science. Each uses your age, sex, weight, and height to calculate calorie burn at rest.

Mifflin‑St Jeor (default) – validated in 1990 on over 500 individuals, this equation is the gold standard for the general population, with an accuracy within ±10% of measured RMR. It works well across ethnicities and body weights.

Cunningham (optional) – requires lean body mass (total weight minus fat mass). Because muscle is far more metabolically active than fat, this formula is especially accurate for athletes or anyone with a known body fat percentage. If you enter your body fat percentage, the calculator can instantly apply the Cunningham equation.

Both formulas output your RMR in calories per day. For weight management, you will later combine that number with your activity level to find total daily energy expenditure.

RMR Formulas in Detail

Here are the exact equations the calculator uses:

Mifflin‑St Jeor

• Men: RMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) + 5
• Women: RMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) − 161

Example: a 30‑year‑old woman, 165 cm, 68 kg → 10×68 + 6.25×165 − 5×30 − 161 = 1,368 kcal/day.

Cunningham

• RMR = 500 + 22 × lean body mass(kg)

This formula skips sex and age entirely because muscle mass drives metabolism. A man with 65 kg of lean mass burns roughly 500 + 22×65 = 1,930 kcal/day.

The calculator above selects the most appropriate equation based on the data you provide.

Factors That Influence Your Metabolic Rate

Your RMR is not a fixed number. Several factors can raise or lower it, sometimes dramatically:

• Lean body mass – the single strongest predictor. Each kilogram of muscle burns about 13 calories/day at rest, versus 4.5 calories for a kilogram of fat.
• Age – after age 20, RMR typically drops 1–3% per decade due to muscle loss. At age 60, the average person’s RMR is about 100–150 calories lower than at 30.
• Sex – men generally have higher RMRs because they carry proportionally more muscle mass. When normalized for lean mass, the difference disappears.
• Hormones – thyroid hormones can shift RMR by 20–30%. Low thyroid function is a common but treatable cause of a sluggish metabolism.
• Diet history – aggressive calorie restriction can lower RMR by 15–20% beyond what weight loss alone would predict. This metabolic adaptation is a key reason crash diets often fail.
• Genetics – studies on twins suggest that about 40–50% of the variation in RMR between individuals is inherited.

Using RMR to Manage Your Weight

Once you know your RMR, adjusting your weight becomes a straightforward math problem:

1. Determine your total daily energy expenditure (TDEE) – multiply your RMR by an activity factor:

   • Sedentary (desk job, little exercise): RMR × 1.2
   • Light activity (1–3 days/week): × 1.375
   • Moderate activity (3–5 days/week): × 1.55
   • Very active (6–7 days/week): × 1.725
   • Extra active (physical job + training): × 1.9

2. Create a calorie deficit for weight loss – subtract 300–500 calories from your TDEE for sustainable fat loss of 0.3–0.5 kg per week. Never eat below your RMR for more than a short period, as that can trigger metabolic slowdown and muscle loss.

3. Add calories for muscle gain – a surplus of 200–400 calories above TDEE, combined with resistance training and adequate protein, supports lean mass growth without excessive fat gain.

This calculator provides estimates based on population averages. Individual metabolism can vary. Always consult a dietitian or physician before making significant dietary changes.