How many calories should I eat to lose weight?

If you’ve ever Googled how many calories should I eat to lose weight, you’ve probably noticed how quickly the answers start to contradict each other. One site tells you 1,200 calories. Another says never go below 1,500. A calculator gives you a number that feels oddly specific, and suddenly you’re wondering whether you’re about to do this properly or completely wrong.

But there isn’t a right number that works for everyone. To lose weight, you need to eat fewer calories than your body uses. But the exact number depends on your body, your activity level, and your health.¹

Step-by-step: how to calculate how many calories you should eat to lose weight

Rather than picking a number out of thin air, weight loss calories are best calculated in three steps.

Step 1: Calculate your basal metabolic rate 

Your basal metabolic rate (BMR) is the number of calories your body needs to keep you alive at rest. For most adults, basal metabolism accounts for around 50-70% of daily energy use. Even when you’re not moving, your body is constantly burning energy, largely by oxidising fatty acids to produce ATP.²

One of the most widely used formulas is the Mifflin–St Jeor equation:³

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

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

This gives you a baseline, not a weight loss target.

Step 2: Work out your total daily energy expenditure 

Your total daily energy expenditure (TDEE) is your BMR plus the calories you burn through movement, work, and exercise. You estimate this by multiplying your BMR by an activity factor:⁴

• Sedentary: ×1.2

• Lightly active (1–3 days/week): ×1.375

• Moderately active (3–5 days/week): ×1.55

• Very active (6–7 days/week): ×1.725

This number reflects how many calories you need to maintain your current weight.

Step 3: Create a safe calorie deficit

To lose weight, you need a calorie deficit, just not an aggressive one. A commonly recommended approach is a 500–1,000 calorie daily deficit, which typically leads to around 0.5-1 kg of weight loss per week.

It’s important to be wary of how quickly you lose weight, because faster weight loss increases the risk of muscle loss, fatigue, nutrient deficiency, and hormonal disruption. Weight loss works best when the deficit is large enough to matter, but small enough to sustain.

Minimum calorie intake: where safety comes first

There’s a lower limit to how much energy your body can function on safely.

Most clinical guidelines advise:⁵

• Women: not regularly below 1,200 calories per day

• Men: not regularly below 1,500 calories per day

Going below this without medical supervision increases the risk of nutrient deficiencies, hormonal suppression, lean muscle loss, and metabolic slowdown. Very low calorie diets may be used in clinical settings, but only under professional oversight.

Why crash dieting backfires

Severely restricting calories can initially lead to rapid weight loss, but it often comes at a cost.

When energy intake drops too low:

• Lean muscle mass is lost alongside fat

• Resting energy expenditure falls

• Hunger hormones increase

• Adherence becomes harder over time

Why calorie needs differ from person to person

Two people eating the same number of calories can see very different results. That’s because calorie needs are influenced by more than height and weight.

Gender and age

Men typically require more calories due to higher lean mass. As we age, muscle mass tends to decline, which lowers energy needs unless activity and resistance training are maintained.⁶

Muscle mass and body composition

Skeletal muscle plays a major role in how your body handles energy. Research shows that abdominal fat tissue constantly releases fatty acids into circulation, and skeletal muscle is one of the main tissues that absorbs and uses them. Increasing muscle demand shifts where fuel is stored after meals, away from fat cells and toward muscle tissue.⁷

This is one reason resistance training supports fat loss even when calorie burn during exercise isn’t dramatic.

Activity timing and lifestyle

Exercise temporarily increases insulin sensitivity in muscle, meaning nutrients are more likely to be directed toward muscle repair and glycogen storage rather than fat storage after meals. This redistribution effect helps explain why people who train consistently often see better body composition outcomes than calorie burn alone would predict.⁸

Moving beyond numbers: why calorie quality matters

Calories determine whether weight is lost or gained. But what you eat influences how manageable that deficit feels.

Protein supports fat loss and muscle preservation

Adequate protein helps preserve lean mass during weight loss and improves satiety. Most adults aiming to lose weight benefit from prioritising protein at each meal.

Fibre and hydration help control appetite

Fibre slows digestion and increases fullness, making calorie control easier without relying on willpower.

Reducing calories without feeling deprived

Small changes add up:

• Choosing lower-energy-dense foods

• Reducing liquid calories

• Eating more slowly

• Structuring meals rather than grazing

The numan take

A calorie deficit drives weight loss, but muscle mass, hormones, stress, sleep, and consistency all influence how your body responds to that deficit. If calorie control feels harder than it should despite doing “everything right”, there may be biological factors at play. Structured, clinically informed support can help bridge that gap safely and effectively.

References

1. Kim JY. Optimal diet strategies for weight loss and weight loss maintenance. J Obes Metab Syndr. 2021;30(1):20–31

2. Molé PA. Impact of energy intake and exercise on resting metabolic rate. Sports Med. 1990;10(2):72–87.

3. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–7. 

4. Ostendorf DM, Caldwell AE, Creasy SA, Pan Z, Lyden K, Bergouignan A, et al. Physical activity energy expenditure and total daily energy expenditure in successful weight loss maintainers. Obesity (Silver Spring). 2019;27(3):496–504. 

5. Chopra S, Malhotra A, Ranjan P, Vikram NK, Singh N. Lifestyle-related advice in the management of obesity: A step-wise approach. J Educ Health Promot. 2020;9(1):239.

6. National Research Council (US) Committee on Diet, Health. Calories: Total macronutrient intake, energy expenditure, and net energy stores. Washington, D.C., DC, USA: National Academies Press; 1989.

7. Harris MB, Kuo C-H. Scientific challenges on theory of fat burning by exercise. Front Physiol. 2021;12:685166.

8. Richter EA, Sylow L, Hargreaves M. Interactions between insulin and exercise. Biochem J. 2021;478(21):3827–46.