To lose weight, you need to eat fewer calories than your body burns each day. The exact number depends on your age, sex, height, weight, and activity level. For most people, that means eating 1,500–2,500 kcal per day with a 500 kcal daily deficit, which produces roughly 0.5 kg (1 lb) of weight loss per week.
That’s the short answer. The longer answer involves some maths, but it’s worth understanding because generic advice like “eat 1,500 calories” could be perfect for one person and dangerously low for another. I came across this calculation a few years ago and it genuinely changed how I thought about portion sizes and what a day of eating should look like.
How to calculate your BMR
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest, just to keep you alive. Breathing, circulation, cell repair. If you lay in bed all day doing absolutely nothing, this is what you’d burn.
The most accurate formula for estimating BMR is the Mifflin-St Jeor equation, recommended by the Academy of Nutrition and Dietetics after a systematic review of 173 studies found it predicted metabolic rate within 10% for 82% of people tested.
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
The older Harris-Benedict equation is still used in some calculators, but it tends to overestimate by about 5%, particularly for people who are overweight.
How to calculate your TDEE
BMR only covers rest. To get your Total Daily Energy Expenditure (TDEE), which is the total number of calories you burn in a day, multiply your BMR by an activity factor:
| Activity level | Multiplier | What it looks like |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise 1–3 days per week |
| Moderately active | 1.55 | Moderate exercise 3–5 days per week |
| Very active | 1.725 | Hard exercise 6–7 days per week |
| Extra active | 1.9 | Physical job + hard training daily |
Your TDEE is your maintenance calories, the amount you’d eat to stay the same weight. Eat below this number and you lose weight. Eat above it and you gain.
Most people overestimate their activity level. If you go to the gym three times a week but sit at a desk the rest of the day, you’re probably “lightly active,” not “moderately active.” When in doubt, round down.
How big should your calorie deficit be?
To lose weight, subtract calories from your TDEE. The size of the deficit determines how fast you lose weight:
| Daily deficit | Weekly weight loss | Who it suits |
|---|---|---|
| 250 kcal | ~0.25 kg (0.5 lb) | Slow and sustainable, minimal hunger |
| 500 kcal | ~0.5 kg (1 lb) | The standard recommendation for most people |
| 750 kcal | ~0.75 kg (1.5 lb) | More aggressive, suitable if you have a lot to lose |
A 500 kcal/day deficit is the most commonly recommended starting point. The NHS recommends a rate of 0.5–1 kg per week for safe, sustainable weight loss.
Don’t go below the safe minimums: 1,200 kcal/day for women and 1,500 kcal/day for men. Below these levels, it becomes very difficult to meet your micronutrient needs through food alone, and the risk of muscle loss, hormonal disruption, and gallstones increases significantly.
Calorie deficit calculation examples
Example 1: 30-year-old woman, 165 cm, 70 kg, moderately active
BMR = (10 × 70) + (6.25 × 165) − (5 × 30) − 161
= 700 + 1,031 − 150 − 161 = 1,420 kcal/day
TDEE = 1,420 × 1.55 = 2,201 kcal/day
For weight loss (500 kcal deficit): 2,201 − 500 = 1,701 kcal/day
This is comfortably above the 1,200 kcal minimum. At this rate, she could expect to lose roughly 0.5 kg per week initially.
Example 2: 35-year-old man, 180 cm, 90 kg, lightly active
BMR = (10 × 90) + (6.25 × 180) − (5 × 35) − 5
= 900 + 1,125 − 175 − 5 = 1,845 kcal/day
TDEE = 1,845 × 1.375 = 2,537 kcal/day
For weight loss (500 kcal deficit): 2,537 − 500 = 2,037 kcal/day
For a more aggressive deficit (750 kcal): 2,537 − 750 = 1,787 kcal/day, still above the 1,500 kcal minimum for men.
Quick reference: calorie targets by body weight
These are estimates for a 500 kcal/day deficit using the Mifflin-St Jeor equation. Assumes age 30 and moderate activity (1.55 multiplier).
| Weight | Height | Sex | BMR | TDEE | Weight loss target |
|---|---|---|---|---|---|
| 60 kg | 160 cm | F | 1,266 | 1,962 | 1,462 |
| 70 kg | 165 cm | F | 1,420 | 2,201 | 1,701 |
| 80 kg | 170 cm | F | 1,575 | 2,441 | 1,941 |
| 70 kg | 175 cm | M | 1,558 | 2,414 | 1,914 |
| 80 kg | 178 cm | M | 1,686 | 2,613 | 2,113 |
| 90 kg | 180 cm | M | 1,845 | 2,860 | 2,360 |
| 100 kg | 183 cm | M | 1,989 | 3,083 | 2,583 |
These figures assume moderate activity. The worked examples above use different activity levels to show how much that single variable changes your target.
Why the “3,500 calories = 1 pound” rule is outdated
You’ve probably heard that a deficit of 3,500 calories equals one pound of fat lost. This comes from a 1958 paper by Max Wishnofsky, and it was the standard rule for decades.
It’s now considered substantially flawed. The rule assumes weight loss is linear: that a 500 kcal/day deficit will keep producing exactly 1 lb/week indefinitely. In reality, your body adapts.
Research by Kevin Hall at the NIH showed the rule overestimates long-term weight loss by roughly 50%. As you lose weight, your metabolism adjusts. Your body burns fewer calories at rest, you move less unconsciously, and hormonal changes make you hungrier. This is called adaptive thermogenesis.
A review of The Biggest Loser contestants found their metabolisms remained suppressed by ~500 kcal/day six years after the show, even in those who regained most of the weight. That’s an extreme case, but more moderate deficits still trigger adaptation, typically 50–100 kcal/day for normal weight loss.
The practical implication: expect your rate of loss to slow over time. You may need to recalculate your targets every 4–6 weeks as your weight changes, or accept a gradually slowing rate of loss.
Factors that affect your calorie needs
The formulas give you a starting point, but several factors can shift your actual needs:
| Factor | Effect on calorie needs |
|---|---|
| Muscle mass | More muscle = higher BMR. 1 kg of muscle burns ~13 kcal/day vs ~4.5 kcal for fat |
| Age | Metabolism is relatively stable from 20–60, then declines ~0.7%/year. The decline before 60 is mostly from muscle loss, not ageing itself |
| NEAT | Non-exercise movement (fidgeting, walking, standing) can vary by 2,000 kcal/day between people. This is the biggest wildcard |
| Protein intake | Protein costs 20–30% of its calories to digest, vs 5–10% for carbs and 0–3% for fat |
| Sleep | Getting 5.5 vs 8.5 hours of sleep led to 55% less fat loss and 60% more muscle loss in one study, on the same calorie deficit |
| Stress | Chronic stress elevates cortisol, promoting visceral fat storage and increasing appetite for high-calorie foods |
Why am I not losing weight in a calorie deficit?
Eating too little. A bigger deficit doesn’t always mean faster results. Going below 1,200–1,500 kcal triggers more aggressive metabolic adaptation, accelerates muscle loss, and often leads to binge-rebound cycles that leave you worse off than when you started.
Overestimating exercise calories. Gym machines and fitness trackers overestimate calorie burn by 27–93%. If you “eat back” all your exercise calories, you’re probably erasing a chunk of your deficit.
Weekend overeating. A 500 kcal/day deficit Monday–Friday creates a 2,500 kcal weekly deficit. Two days of eating 1,250 kcal above maintenance on the weekend (entirely plausible with meals out and drinks) wipes it out entirely. Net result: zero weight loss.
Not accounting for liquid calories. A daily latte (200 kcal), a glass of juice (110 kcal), and a glass of wine (125 kcal) adds 435 kcal, nearly your entire deficit, without feeling like you’ve eaten anything.
Calculate your target
Use the calculator below to get your personal numbers. It uses the Mifflin-St Jeor equation with the standard activity multipliers covered above.
TDEE Calculator
Based on the Mifflin-St Jeor equation, recommended by the Academy of Nutrition and Dietetics.
Maintenance
—
kcal/day
BMR
—
kcal/day
For weight loss
Mild deficit
~0.25 kg/week
— kcal
Moderate deficit
~0.5 kg/week (recommended)
— kcal
Aggressive deficit
~0.75 kg/week
— kcal
These are estimates. Your actual needs may vary based on muscle mass, genetics, and other factors. Consult a healthcare professional before starting any diet.
How to stick to your calorie target
You’ve got a number. Now you need to eat around that number most days. That’s where most people struggle, not because they lack willpower, but because tracking what you eat is tedious.
If you want a detailed look at different tracking methods, I wrote about how to track calories without an app. And if you’re curious about whether AI tools can make it easier, I covered what actually works in AI calorie tracking.
The short version: the method matters less than whether you stick with it. If you want something with near-zero friction, you can text Nemo what you ate on WhatsApp (a photo, voice note, or quick text) and he’ll keep a running daily total against your target. No app to download, no food databases to search.
Frequently asked questions
How many calories should I eat to lose 1 kg per week?
You need a daily deficit of approximately 1,000 kcal below your TDEE to lose 1 kg per week. For most people, this means eating 1,500–2,000 kcal per day, depending on body size and activity level. This is an aggressive rate and may not be sustainable long-term. A deficit of 500 kcal/day (0.5 kg/week) is recommended for most people.
Is 1,200 calories a day enough?
1,200 kcal/day is the generally accepted minimum for women and should not be attempted without awareness of the nutritional limitations. At 1,200 kcal, meeting all micronutrient needs through food alone is difficult. For men, the minimum is 1,500 kcal/day. If your calculated target falls near these thresholds, consider a smaller deficit combined with increased activity.
Why am I not losing weight in a calorie deficit?
The most common reasons: you’re consuming more calories than you think (cooking oils, sauces, liquid calories, and weekend overeating are the usual culprits), your exercise calorie estimates are too high, or your body has adapted to the deficit over time. Try recalculating your TDEE at your current weight, tracking more carefully for one week, and checking whether weekends are undoing your weekday deficit.
Should I eat back calories I burn during exercise?
Generally, no. At most, eat back half. Fitness trackers overestimate calorie burn by 27–93%. If you eat back all your exercise calories based on a tracker reading, you’re likely eating at or near maintenance. Your activity multiplier already accounts for general exercise when calculating TDEE.
How often should I recalculate my calorie target?
Every 4–6 weeks, or whenever you’ve lost 3–5 kg. As you lose weight, your BMR decreases (a lighter body needs fewer calories), and adaptive thermogenesis further reduces your expenditure. What was a 500 kcal deficit at 90 kg may only be a 300 kcal deficit at 82 kg.
