BMR, TDEE, and calorie deficit

Weight change ultimately comes down to energy balance over time. To plan intake, you need an estimate of how much energy your body burns. Two numbers dominate casual planning: BMR (basal metabolic rate) and TDEE (total daily energy expenditure).

BMR — resting burn

BMR is energy used at rest for breathing, circulation, and organ function. Our BMR & TDEE calculator uses the Mifflin–St Jeor equation (1990), which is widely used in apps and dietetics coursework:

• Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5
• Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161

Older Harris–Benedict and Katch–McArdle (needs body-fat %) equations exist; Mifflin–St Jeor is the default here for simplicity.

TDEE — adding activity

TDEE ≈ BMR × activity factor. Typical multipliers:

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

These are estimates. Wearables and metabolic testing can refine them but are not required for a first pass.

Deficit and surplus

Rough rule: 7,700 kcal ≈ 1 kg of fat tissue change (often rounded to 3,500 kcal per pound in US sources). A daily deficit of 500 kcal might yield ~0.5 kg per week — theory only; water, glycogen, and adherence shift the scale. Our Weight Change Timeline tool applies this approximation from your current weight, goal, and chosen deficit.

Worked example

Woman, 35 years, 70 kg, 165 cm: BMR ≈ (700) + (1031) − (175) − 161 ≈ 1,395 kcal. With moderate activity (×1.55), TDEE ≈ 2,162 kcal. Eating ~1,660 kcal daily (−500) is a common starting deficit — adjust with hunger, performance, and medical guidance.

FAQs

Should I eat below BMR?

Many people do during weight loss, but very low intake deserves professional oversight.

Do macros matter?

Total calories drive weight trend; protein and training affect lean mass retention — see our Macro Calculator.

Why did my loss stall?

Metabolic adaptation, logging error, and water retention all mask fat loss temporarily.

Sources

Mifflin et al., 1990; FAO/WHO energy requirements; NHS weight-loss pacing guidance.