Why Most Calorie Advice Gives You the Wrong Number
If you have ever searched "how many calories should I eat to lose weight" you have probably seen the answer 1,200 calories for women and 1,500 for men repeated across dozens of websites. These numbers are not personalised to you — they are generic figures that originated from outdated research and get recycled without context.
The actual number of calories you need to lose weight is different for every person. It depends on your age, sex, current weight, height and how active you are. Someone who is 5'4", 60kg and sedentary needs a completely different calorie intake than someone who is 5'10", 90kg and works out five days a week.
Getting this number right is the foundation of any effective weight loss plan. Get it wrong and you either lose weight too slowly to stay motivated, or you eat so little that your body adapts, your metabolism slows and weight loss stalls.
Here is the science-backed method for calculating your number correctly.
Step 1 — Calculate Your BMR (Basal Metabolic Rate)
Your BMR is the number of calories your body burns just to stay alive — to keep your heart beating, your lungs breathing and your organs functioning — with no physical activity at all. Think of it as the calories you would burn lying completely still for 24 hours.
The most accurate formula for calculating BMR is the Mifflin-St Jeor equation, which has been validated in multiple studies as more accurate than older formulas:
For men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
For women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161
Example: A 30-year-old woman, 65kg, 165cm tall: BMR = (10 x 65) + (6.25 x 165) - (5 x 30) - 161 BMR = 650 + 1031.25 - 150 - 161 = 1,370 calories per day
This means her body burns approximately 1,370 calories per day just to keep functioning, before any activity.
Step 2 — Calculate Your TDEE (Total Daily Energy Expenditure)
Your BMR only accounts for basic survival. Your TDEE is your actual total daily calorie burn — everything you do in a day including walking, working, exercising and even digesting food. TDEE is the number that actually matters for weight management.
To calculate TDEE, multiply your BMR by an activity multiplier:
Sedentary (desk job, little or no exercise): BMR x 1.2 Lightly active (light exercise 1-3 days/week): BMR x 1.375 Moderately active (moderate exercise 3-5 days): BMR x 1.55 Very active (hard exercise 6-7 days/week): BMR x 1.725 Extremely active (physical job + daily training): BMR x 1.9
Using our example: 1,370 x 1.375 (lightly active) = 1,884 calories/day TDEE.
This means she burns approximately 1,884 calories per day going about her normal life. If she eats exactly 1,884 calories, her weight stays the same.
Step 3 — Create a Calorie Deficit for Weight Loss
To lose weight, you need to eat fewer calories than you burn. The difference between what you eat and what you burn is your calorie deficit. Fat loss occurs when you sustain a deficit over time.
The science behind the numbers: one pound of body fat contains approximately 3,500 calories. To lose one pound per week, you need a deficit of 500 calories per day (500 x 7 = 3,500).
Practical deficit targets:
Slow and sustainable (0.25-0.5kg per week): 250-500 calorie daily deficit Moderate (0.5-0.75kg per week): 500-750 calorie daily deficit Aggressive (max recommended, 1kg per week): 750-1000 calorie daily deficit
For our example: 1,884 - 500 = 1,384 calories per day to lose approximately 0.5kg per week.
Important: Do not go below 1,200 calories for women or 1,500 calories for men without medical supervision. Below these thresholds, it becomes very difficult to meet your nutritional requirements, muscle loss accelerates and metabolic adaptation kicks in more aggressively.
How to Calculate Your Calorie Target Using TrendPro
Instead of doing this calculation manually, our free Calorie Calculator at trendproservices.co.uk/tools/calorie-calculator does everything automatically.
Enter your age, sex, weight and height, select your activity level, and the calculator instantly shows your BMR, your TDEE and your recommended calorie intake for weight loss, maintenance and weight gain.
The calculator uses the Mifflin-St Jeor equation — the same formula used in the manual calculation above — and gives you results in both metric (kg, cm) and imperial (lbs, feet/inches) units. You also get your BMR and macronutrient guidance alongside the calorie targets.
It takes about 30 seconds and gives you a personalised number based on your actual measurements — not a generic figure copied from a 1950s study.
Why Your Calorie Target Changes Over Time
Here is something many calorie guides do not tell you: your TDEE changes as you lose weight, and you need to recalculate it periodically.
When you weigh less, your BMR decreases because your body requires fewer calories to sustain a smaller mass. This is why weight loss slows down over time even if you eat exactly the same amount — the deficit gets smaller as your bodyweight drops.
A practical approach: Recalculate your TDEE every 4-6 weeks or every 5kg of weight loss. Update your calorie target accordingly. This keeps you in a genuine deficit as your body changes.
The Role of Protein in a Calorie Deficit
Calories matter most for weight loss, but protein is the most important macronutrient within those calories.
When you are in a calorie deficit, your body can break down muscle tissue alongside fat tissue for energy. Higher protein intake significantly reduces muscle loss during weight loss, keeps you feeling fuller for longer (protein is the most satiating macronutrient), and has the highest thermic effect of any macronutrient — meaning your body burns more calories digesting protein than it does digesting carbs or fat.
A practical target: aim for 1.6-2.2 grams of protein per kilogram of bodyweight per day when in a calorie deficit. For our 65kg example, that is 104-143 grams of protein per day within the 1,384 calorie target.
Common Calorie Calculation Mistakes
Using a generic number — 1,200 or 1,500 calories is not your TDEE minus a deficit. It is a random number that might put you in a 200-calorie deficit or an 800-calorie deficit depending on your body and activity level. Always calculate your personal TDEE first.
Overestimating activity level — Most people select "moderately active" when they are actually sedentary or lightly active. Gym sessions 3 times per week while sitting at a desk all day is lightly active, not moderately active. Overestimating activity creates a smaller deficit than intended and slows results.
Forgetting to include liquid calories — Drinks like orange juice, lattes, smoothies and alcohol contain significant calories that are easy to forget. A daily latte can add 200-300 calories and eliminate half your deficit.
Not recalculating as weight changes — As covered above, your TDEE decreases as you lose weight. Sticking to the same calorie target without recalculating leads to a stalling plateau after the first few months.
Eating too little — Creating a 1,000+ calorie deficit feels logical for faster results but typically backfires. Extreme deficits cause muscle loss, hormonal disruption, fatigue and intense hunger that makes the deficit unsustainable. Slower and steady consistently outperforms aggressive cutting.
Frequently Asked Questions
How accurate is the Mifflin-St Jeor equation? It is the most accurate widely available formula for estimating BMR in healthy adults, validated across multiple independent studies. However, it is still an estimate — individual metabolic rates vary by 10-15% even between people with identical measurements. If your actual results over 4-6 weeks do not match the prediction, adjust your calorie target up or down by 100-200 calories until the rate of change matches your target.
Should I eat back calories burned during exercise? It depends on how you set your activity multiplier. If you used your activity level including your workouts in the TDEE calculation (e.g. "moderately active"), your exercise calories are already factored in — do not eat them back. If you used "sedentary" and add exercise on top, eating back around 50-75% of exercise calories is reasonable since gym trackers typically overestimate burn.
How long until I see results? Most people see measurable changes within 2-4 weeks of maintaining a genuine calorie deficit. The first 1-2 weeks often show rapid drops due to water weight changes as glycogen stores deplete. True fat loss becomes visible after 3-4 weeks of consistent deficit.
What is the difference between TDEE and BMR? BMR is the calories burned at complete rest — pure biological survival. TDEE is BMR multiplied by an activity factor — your actual total daily burn including all movement and exercise. TDEE is the number you use to set a calorie target. BMR alone is not your daily burn.
Can I lose weight without counting calories? Yes. Calorie counting is one method, not the only method. Approaches like eating whole foods and eliminating ultra-processed food, intermittent fasting and low-carbohydrate diets all create calorie deficits indirectly without explicit counting. However, if you are not losing weight with another approach, calculating your TDEE and tracking intake for a few weeks is the fastest way to diagnose the problem.