How Many Calories to Lose Weight: Calculating Your Target With Evidence

Knowing how many calories to eat for weight loss requires calculating your individual energy expenditure — not applying a generic number. The evidence provides a validated calculation method, evidence-based deficit targets, safe minimum thresholds, and guidance on recalibration as weight changes.

Step 1: Calculate Your Basal Metabolic Rate (BMR)

BMR is the energy your body uses at complete rest to maintain vital functions. The Mifflin-St Jeor equation (1990) is the most accurate predictive equation for adults in clinical and research settings:

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

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

Example — 40-year-old woman, 80 kg, 165 cm: BMR = (10 × 80) + (6.25 × 165) − (5 × 40) − 161 = 800 + 1,031 − 200 − 161 = 1,470 kcal/day

Example — 40-year-old man, 90 kg, 178 cm: BMR = (10 × 90) + (6.25 × 178) − (5 × 40) + 5 = 900 + 1,112 − 200 + 5 = 1,817 kcal/day

Step 2: Apply an Activity Multiplier to Get TDEE

Total Daily Energy Expenditure (TDEE) accounts for all physical activity on top of BMR. Multiply your BMR by the appropriate factor:

Activity level	Description	Multiplier
Sedentary	Desk job; little or no deliberate exercise	1.2
Lightly active	Light exercise 1–3 days/week; some daily walking	1.375
Moderately active	Moderate exercise 3–5 days/week	1.55
Very active	Hard exercise 6–7 days/week; physical job	1.725
Extremely active	Very hard exercise daily + physical occupation	1.9

Example (continuing from above — woman, sedentary office job with 2 gym sessions/week): TDEE = 1,470 × 1.375 = 2,021 kcal/day

Important: Most people overestimate their activity level. "Moderately active" requires genuine daily activity, not just occasional exercise. For sedentary office workers who exercise 2–3 times/week, 1.375 is typically more accurate than 1.55.

Step 3: Apply the Evidence-Based Deficit

NICE CG189 (Obesity: identification, assessment and management) recommends a calorie deficit producing weight loss of 0.5–1 kg per week.

Fat contains approximately 7,700 kcal/kg (adipose tissue is not pure fat — the combined energy content including associated water and protein averages approximately 7,000–7,700 kcal/kg).

To lose 0.5–1 kg/week: requires a deficit of approximately 500–750 kcal/day.

Continuing the example:

TDEE = 2,021 kcal/day
500 kcal deficit: 2,021 − 500 = 1,521 kcal/day target
750 kcal deficit: 2,021 − 750 = 1,271 kcal/day target

For this individual, a target of approximately 1,400–1,600 kcal/day is a reasonable starting range.

Safe Minimum Calorie Intakes

Eating below a minimum threshold risks lean mass loss, nutrient deficiency, and unsustainable hunger that leads to abandonment.

NHS and NICE guidance on minimum intakes:

Women: Not below 1,200 kcal/day without medical supervision
Men: Not below 1,500 kcal/day without medical supervision

Very low calorie diets (VLCDs) of 800 kcal/day are used in supervised NHS programmes (such as Tier 3 Obesity services) with meal replacement products (Cambridge, Lighter Life) and regular clinical monitoring. These are not appropriate for unsupervised use.

Why minimums matter: Below 1,200 kcal/day it becomes very difficult to achieve adequate protein (1.6–2.0g/kg/day — which at 80 kg requires 128–160g protein/day = approximately 512–640 kcal from protein alone), let alone fibre, micronutrients, and sufficient fat for hormone function.

Worked Example: Full Calculation

Profile: 35-year-old man, 95 kg, 180 cm, office worker, 3 gym sessions/week. Goal: lose 1 kg/week.

BMR: = (10 × 95) + (6.25 × 180) − (5 × 35) + 5 = 950 + 1,125 − 175 + 5 = 1,905 kcal/day

TDEE (lightly active, 1.375): = 1,905 × 1.375 = 2,619 kcal/day

Target for ~0.75 kg/week loss: = 2,619 − 750 = 1,869 kcal/day

Protein target (1.7g/kg × 95 kg = 162g/day = 648 kcal from protein)

Remaining calories for carbohydrate and fat: = 1,869 − 648 = 1,221 kcal (~40% carbohydrate, ~30% fat)

Accuracy: What Affects the Calculation

The Mifflin-St Jeor equation has a standard error of approximately ±10% in validation studies. For a person with a calculated TDEE of 2,000 kcal/day, the actual value may be 1,800–2,200 kcal/day.

Sources of individual variation:

Lean mass: Mifflin-St Jeor uses total weight, not lean mass. At the same height, weight, age, and sex, a person with more lean mass has a higher BMR than the equation predicts.
NEAT (non-exercise activity thermogenesis): Varies by 350–750 kcal/day between individuals (Levine 1999, Science) — impossible to capture with a multiplier
Metabolic adaptation: Already-adapted individuals (people who have previously lost significant weight) may have a suppressed TDEE below what the equation predicts

The practical approach: Use the calculation as a starting point, then track actual weight change over 3–4 weeks. If losing less than 0.25 kg/week consistently, reduce intake by 100–150 kcal/day or increase activity by an equivalent amount.

Metabolic Adaptation: Why Recalibration Is Necessary

Leibel et al. (1995, NEJM, n=18): After 10% weight loss, TDEE fell by approximately 250 kcal/day beyond what lean mass loss alone predicted — from NEAT reduction, improved exercise efficiency, and altered thyroid hormone activity.

Practical implication: At 95 kg, TDEE is approximately 2,619 kcal/day. After losing 10 kg (to 85 kg), the new TDEE is not simply recalculated from the Mifflin-St Jeor equation — it may be 200–300 kcal/day lower than that calculation suggests, due to adaptation.

Recalibrate every 5–10 kg of weight lost:

Recalculate BMR using current weight
Multiply by appropriate activity factor
Reduce by 500–750 kcal/day for the new target
Adjust for any change in activity level

Why Calorie Counting Is Imprecise — and Still Useful

Food label accuracy: EU/UK regulations permit a 20% tolerance on stated calorie values. A food labelled as 200 kcal may legally contain 160–240 kcal.

Estimation errors: Oils (1 tablespoon varies from 120 to 250 kcal depending on poured quantity), nuts (a "handful" varies 2–3× in weight), and restaurant meals (portions vary substantially) are major sources of underestimation.

Despite imprecision, calorie tracking works: Studies using calorie tracking consistently show better weight loss outcomes than unmonitored diets. The value is in building awareness of portion sizes and high-calorie foods — not precision to the nearest calorie. Weighing oils, nuts, and nut butters with a kitchen scale significantly improves accuracy in the areas that matter most.

Tracking apps (UK): MyFitnessPal (largest UK food database), Nutracheck (UK-specific database, subscription), Cronometer (comprehensive micronutrient tracking alongside calories).

Summary: Calorie Target Framework

Step	Action	Example (35F, 80 kg, 165 cm, lightly active)
1	Calculate BMR (Mifflin-St Jeor)	1,470 kcal
2	Apply activity multiplier	× 1.375 = 2,021 kcal (TDEE)
3	Apply deficit (500–750 kcal/day)	1,271–1,521 kcal
4	Check against minimum (≥1,200 kcal women)	1,271 is borderline; use 1,400 kcal
5	Verify protein target is achievable	1.7 × 80 = 136g = 544 kcal; feasible within budget
6	Track for 3–4 weeks and adjust if loss <0.25 kg/week	—
7	Recalculate every 5–10 kg lost	—

Disclaimer: This article is for informational and educational purposes only. People with diabetes, cardiovascular disease, kidney disease, or eating disorder history should work with a GP or registered dietitian to set safe calorie targets.