Calorie Deficit Calculator
How many calories should you eat to lose weight?
Enter your body stats and see your personalised calorie deficit in seconds. Get your Total Daily Energy Expenditure (TDEE), daily calorie target, complete protein/carbs/fat macro breakdown, and a visual week-by-week weight loss timeline. Choose between mild, moderate, and aggressive deficit levels and instantly see how each one changes your timeline.
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How It Works
The TDEE & Calorie Deficit Formula
The validated science behind every calculation
Formula
Step 1 — BMR (Mifflin-St Jeor): Men: BMR = (10 × W) + (6.25 × H) − (5 × A) + 5 Women: BMR = (10 × W) + (6.25 × H) − (5 × A) − 161 Step 2 — TDEE: TDEE = BMR × Activity Multiplier Step 3 — Calorie Target: Daily Target = TDEE − Deficit (250 / 500 / 750 kcal) Step 4 — Weekly Fat Loss: Kg per week = (Deficit × 7) ÷ 7,700
Variables
Basal Metabolic Rate
The number of calories your body burns at complete rest — keeping your heart beating, lungs breathing, brain functioning, and body temperature regulated. BMR accounts for approximately 60–75% of total daily calorie expenditure for most people. The Mifflin-St Jeor equation is the most clinically validated formula for BMR estimation, preferred over the older Harris-Benedict equation by the Academy of Nutrition and Dietetics since 2005.
Total Daily Energy Expenditure
Your total daily calorie burn including BMR, physical activity, and the thermic effect of food (calories burned digesting meals, approximately 10% of total intake). TDEE is calculated by multiplying BMR by an activity factor: Sedentary (desk job, no exercise) × 1.2; Lightly active (1–3 days exercise/week) × 1.375; Moderately active (3–5 days) × 1.55; Very active (6–7 days intense) × 1.725; Extremely active (twice daily or physical labour) × 1.9.
Calorie Deficit
The daily calorie reduction below your TDEE. A deficit of 500 calories/day creates a weekly shortfall of 3,500 calories, which corresponds to approximately 0.45 kg (1 lb) of fat loss per week — since 1 lb of body fat stores approximately 3,500 calories of energy. This 'pound per week per 500-calorie deficit' rule is a useful approximation, though actual fat loss varies due to water retention, metabolic adaptation, and body composition changes.
Protein Target (grams)
Calculated at 1.6g per kg of goal body weight (evidence-based minimum for muscle preservation during a calorie deficit). Higher protein (2.0–2.4g/kg) is recommended for individuals doing resistance training. Each gram of protein provides 4 calories. Maintaining adequate protein during a deficit is the single most important nutritional factor for preserving muscle mass while losing fat.
Fat Target (grams)
Calculated at 25–30% of total daily calories. Dietary fat is essential for hormone production (including testosterone, oestrogen, and cortisol regulation), fat-soluble vitamin absorption (A, D, E, K), and cell membrane integrity. Dropping fat intake below 15% of total calories is associated with hormonal disruption, particularly in women. Each gram of fat provides 9 calories.
Carbohydrate Target (grams)
The remaining calories after protein and fat are allocated. Carbohydrates provide the primary fuel for high-intensity exercise, brain function, and daily activity. Each gram of carbohydrate provides 4 calories. During a calorie deficit, carbohydrate intake naturally decreases, which — combined with glycogen depletion — accounts for the rapid initial weight loss in the first 1–2 weeks of any diet (water weight, not fat).
Note: The Mifflin-St Jeor equation has a margin of error of approximately ±10% for most individuals. People with unusually high or low muscle mass may find their actual TDEE differs from the calculated estimate. If after 3–4 weeks of consistent tracking your weight is not changing as predicted, adjust your calorie target by ±100 calories and reassess.
Example: 80kg Man, 175cm, 30 Years Old, Moderately Active — Goal: 70kg
Complete step-by-step calorie deficit calculation
Calculate BMR (Mifflin-St Jeor, male)
BMR = (10 × 80) + (6.25 × 175) − (5 × 30) + 5 = 800 + 1,093.75 − 150 + 5 = 1,748 kcal/day
Apply activity multiplier (moderately active, 3–5 days/week)
TDEE = 1,748 × 1.55 = 2,709 kcal/day (maintenance calories)
Apply moderate deficit (−500 kcal)
Daily target = 2,709 − 500 = 2,209 kcal/day
Calculate weekly fat loss rate
500 cal/day × 7 days = 3,500 cal/week ÷ 7,700 cal/kg = 0.45 kg per week
Calculate time to goal (10kg to lose)
10 kg ÷ 0.45 kg/week = 22 weeks (approximately 5.5 months)
Calculate macro targets at 2,209 kcal
Protein: 70kg × 1.6g = 112g (448 kcal) | Fat: 2,209 × 28% ÷ 9 = 69g (621 kcal) | Carbs: (2,209 − 448 − 621) ÷ 4 = 285g (1,140 kcal)
Reference Guide
| unit | value | note |
|---|---|---|
| Maintenance (TDEE) | 2,709 kcal/day | No loss or gain at this level |
| Mild deficit (−250) | 2,459 kcal/day | ~0.23 kg/week — 44 weeks to goal |
| Moderate deficit (−500) | 2,209 kcal/day | ~0.45 kg/week — 22 weeks to goal |
| Aggressive deficit (−750) | 1,959 kcal/day | ~0.68 kg/week — 15 weeks to goal |
| Protein (goal weight) | 112g/day | 1.6g per kg of goal weight (70kg) |
| 3 meals/day | 736 kcal/meal | 2,209 ÷ 3 meals |
Choosing Your Deficit Level
The right deficit depends on your timeline, lifestyle, and starting point
A 250 kcal deficit produces approximately 0.23 kg (0.5 lb) of fat loss per week. This is the gentlest approach — barely noticeable in terms of hunger, energy, or social eating. It works best for people who are already close to their goal weight, those with active lifestyles who cannot afford to lose performance, or those who have failed aggressive diets repeatedly and need a sustainable long-term approach. The slower pace means the body has minimal reason to lower its metabolic rate.
Best for: 5kg or less to lose; athletes; those with poor history of adherence to strict diets; maintenance with slight downward trend.
A 500 kcal deficit produces approximately 0.45 kg (1 lb) of fat loss per week — the most frequently recommended rate in clinical nutrition literature. This level is achievable through a combination of modest dietary reduction and moderate activity, is sustainable for months, and produces meaningful results (roughly 2kg per month). At this level, hunger is manageable, energy levels remain mostly stable, and muscle mass preservation is good when protein intake is adequate.
Best for: Most people seeking sustainable fat loss. The optimal balance of speed, sustainability, and muscle preservation for 90% of individuals.
A 750 kcal deficit produces approximately 0.68 kg (1.5 lbs) of fat loss per week. This is the upper limit recommended for most individuals without medical supervision. At this level, hunger is significant and constant dietary discipline is required. The risk of muscle loss increases, particularly without resistance training and high protein intake. Fatigue, reduced workout performance, and lower mood are common side effects. This level is appropriate for individuals with a meaningful amount of weight to lose and a clear short-term timeline.
Best for: Significant weight loss (10kg+) with a defined deadline; those with medical urgency; must be combined with high protein (2g/kg) and resistance training.
Calorie targets below 1,200 kcal/day for women or 1,500 kcal/day for men are generally considered unsafe without medical supervision. At these levels, it becomes extremely difficult to meet essential nutrient requirements, the body significantly downregulates metabolism (metabolic adaptation), and muscle loss accelerates dramatically. Very low calorie diets (VLCDs) should only be undertaken under medical supervision. Our calculator will flag if your settings approach these thresholds.
Best for: Not recommended without medical supervision.
The Science of Calorie Deficit and Fat Loss
The calorie deficit model of weight loss rests on one of the most robustly validated principles in nutritional science: the First Law of Thermodynamics applied to human metabolism. When energy intake (calories consumed) is consistently less than energy expenditure (calories burned), the body draws on stored energy — primarily body fat — to make up the shortfall. This principle has been confirmed by controlled metabolic ward studies, where subjects' food intake and activity are precisely measured, consistently showing that sustained calorie deficits produce predictable fat loss. The Mifflin-St Jeor equation, published in 1990 in the American Journal of Clinical Nutrition, remains the most accurate widely-available formula for estimating BMR across diverse adult populations. A 2005 review by the Academy of Nutrition and Dietetics (Frankenfield et al.) compared five BMR prediction equations across 10 studies and found Mifflin-St Jeor to be the most accurate for 82% of subjects tested — significantly outperforming the previously standard Harris-Benedict equation. The role of protein during a calorie deficit deserves particular emphasis. Research by Layman et al. (2003) and the comprehensive meta-analysis by Morton et al. (2018) demonstrate that dietary protein above 1.6g per kg of body weight is the most effective intervention for preserving lean muscle mass during weight loss — more effective than any specific training protocol or supplement. Protein also has the highest thermic effect of any macronutrient (20–30% of calories consumed are used in digestion), making it doubly valuable during a deficit. Metabolic adaptation — sometimes called 'adaptive thermogenesis' — is a clinically documented phenomenon where the body responds to sustained calorie restriction by reducing its metabolic rate beyond what would be predicted from body weight changes alone. Research by Leibel et al. (1995) and Rosenbaum et al. (2010) showed that individuals who lost 10% of body weight experienced a metabolic rate reduction 10–15% greater than would be expected from the weight loss alone. This is why many people hit weight loss plateaus: their TDEE has decreased. The practical solution is to either recalculate TDEE at the new body weight, take a maintenance break, or incorporate diet breaks.
Key Features
💡 Pro Tips
- →Track your actual weight daily and take a 7-day average — daily weight fluctuates by 1–3kg due to water, salt, and digestive content. A weekly average reveals the true trend and prevents the emotional noise of daily weigh-ins from derailing your progress.
- →Recalculate your TDEE every 5–7kg of weight lost. As your body mass decreases, your BMR and therefore your TDEE also decrease. The 500-calorie deficit that worked at 90kg may have become only a 300-calorie deficit by the time you reach 80kg — stalling your progress without any change in your diet.
- →Treat your first 2 weeks of results with scepticism. Rapid initial weight loss is almost always water and glycogen depletion, not fat. Glycogen (stored carbohydrates in muscles and liver) holds approximately 3–4 times its weight in water. Reducing carbohydrate intake dumps this water, creating rapid scale drops that are not fat loss. True fat loss pace becomes visible from week 3 onwards.
- →Prioritise protein above all other dietary targets. If you only have one macro rule to follow, hit your protein target. High protein preserves muscle during a deficit, has the highest satiety per calorie of any macronutrient, and has the highest thermic effect (you burn 20–30% of protein calories in digestion). Every other macro can flex — protein cannot.
- →Consider 'diet breaks': deliberately eating at maintenance for 1–2 weeks every 6–8 weeks of deficit eating. Research by Byrne et al. (2017) found that this 'two weeks on, two weeks at maintenance' approach produced greater fat loss than continuous restriction over the same period, with significantly better metabolic rate preservation.
Common Mistakes
Not tracking calories accurately, especially liquids and condiments
Research by Lichtman et al. (1992) found that obese subjects underreported calorie intake by an average of 47% and overestimated activity by 51%. Cooking oils (1 tablespoon = 120 calories), salad dressings, alcohol, and coffee drinks are the most frequently underestimated items. For the first 2–4 weeks of a deficit, precise tracking (weighing food on a scale, not estimating portions) is essential to establish accurate baselines.
Setting an aggressive deficit immediately without building adherence habits first
A 750-calorie deficit that is abandoned after 10 days produces zero fat loss. A 300-calorie deficit maintained consistently for 6 months produces 7–8kg of fat loss. Adherence is the most important variable in any diet — more important than the deficit size, macro ratio, or meal timing. Start at a moderate deficit and only increase it if adherence is consistent and progress stalls.
Ignoring protein targets and focusing only on calorie totals
Two people eating identical calorie deficits will achieve very different body composition outcomes if their protein intakes differ. The person eating 150g protein/day will lose mostly fat while preserving muscle; the person eating 60g protein/day will lose a significant portion of muscle alongside fat, resulting in a 'skinny fat' outcome rather than a lean physique. Protein is not optional during a deficit — it is the most important variable.
Eating back all exercise calories tracked by fitness devices
Fitness trackers (Fitbit, Apple Watch, Garmin) systematically overestimate calorie burn during exercise by 27–93% depending on the activity (Reed & Hill, 2019). If you track a 45-minute run as 600 calories burned and eat all of it back, you may actually be eliminating your deficit entirely. A conservative approach: eat back 50% of tracked exercise calories and monitor weekly scale trends.
Giving up after 1–2 weeks because the scale is not moving
The first 2 weeks of a deficit often show confusing scale results due to water retention changes, hormonal fluctuations (particularly in women during the menstrual cycle), and digestive content variation. Fat loss only becomes consistently visible on the scale after 3–4 weeks of consistent behaviour. Judge progress over 4-week blocks, not daily or weekly fluctuations.
Research & Citations
All factual claims on this page are sourced from peer-reviewed research
- [1]
Mifflin, M.D., St Jeor, S.T., Hill, L.A., Scott, B.J., Daugherty, S.A., Koh, Y.O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), pp. 241–247.
Original publication of the Mifflin-St Jeor equation — the primary formula used in this calculator
View source - [2]
Frankenfield, D., Roth-Yousey, L., Compher, C. (2005). Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults. Journal of the American Dietetic Association, 105(5), pp. 775–789.
Validated Mifflin-St Jeor as most accurate BMR prediction equation for 82% of subjects across 10 clinical studies
View source - [3]
Morton, R.W., Murphy, K.T., McKellar, S.R., Schoenfeld, B.J., Henselmans, M., Helms, E., et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 52(6), pp. 376–384.
Comprehensive meta-analysis establishing 1.62g protein/kg/day as optimal for muscle preservation — basis for our protein calculation
View source - [4]
Byrne, N.M., Sainsbury, A., King, N.A., Hills, A.P., Wood, R.E. (2018). Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. International Journal of Obesity, 42(2), pp. 129–138.
Diet break research — two weeks on/two weeks maintenance approach produced superior fat loss with better metabolic rate preservation
View source - [5]
U.S. Department of Agriculture and U.S. Department of Health and Human Services (2020). Dietary Guidelines for Americans 2020–2025. dietaryguidelines.gov.
Official macronutrient distribution guidelines — basis for carbohydrate, fat, and protein percentage recommendations
View source
This calculator is a reference tool and does not constitute medical advice. For personalised sleep health guidance, consult a qualified healthcare provider.
Frequently Asked Questions
How do I calculate my calorie deficit?
Step 1: Calculate your BMR using Mifflin-St Jeor: Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. Women: same formula but −161 instead of +5. Step 2: Multiply BMR by your activity factor (1.2 to 1.9) to get your TDEE (maintenance calories). Step 3: Subtract 250–750 calories from your TDEE to create your deficit. Our calculator does all of this automatically in under 45 seconds.
How many calories should I eat to lose 1kg per week?
1kg of body fat stores approximately 7,700 calories. To lose 1kg per week, you need a daily deficit of 7,700 ÷ 7 = 1,100 calories. This is a large deficit — for most people it would require eating less than 1,500 calories/day, which is difficult to sustain and risks muscle loss. The standard recommendation is 0.5kg/week (500 cal/day deficit) for sustainable fat loss. Losing more than 1% of body weight per week consistently increases the risk of muscle loss significantly.
What is a good calorie deficit for weight loss?
The most evidence-based calorie deficit for sustainable weight loss is 500 calories per day below your TDEE (maintenance calories). This produces approximately 0.45kg (1 lb) of fat loss per week, is achievable without extreme dietary restriction, allows adequate protein and nutrient intake, and minimises muscle loss when protein targets are met. Larger deficits (750+ cal/day) accelerate fat loss but require more discipline and increase the risk of muscle loss and metabolic adaptation.
What should my macros be in a calorie deficit?
For optimal fat loss while preserving muscle: Protein should be 1.6–2.0g per kg of body weight (or goal weight if losing significant mass) — this is non-negotiable. Fat should be at least 0.7–1.0g per kg of body weight, minimum, to maintain hormonal health — this represents approximately 25–30% of total calories. Carbohydrates fill the remaining calories. Our calculator automatically calculates your personal macro targets based on your calorie level and body weight.
How long will it take to lose 10kg?
At a moderate 500 calorie/day deficit, you lose approximately 0.45kg of fat per week. 10kg ÷ 0.45kg/week = approximately 22 weeks (about 5.5 months). At an aggressive 750 calorie/day deficit: 10kg ÷ 0.68kg/week = approximately 15 weeks. At a mild 250 calorie/day deficit: approximately 44 weeks. Our calculator shows your personalised timeline for all three deficit levels based on your actual TDEE.
Does a calorie deficit cause muscle loss?
A calorie deficit alone does cause some muscle loss — this is unavoidable during weight loss. However, two factors dramatically minimise it: high protein intake (1.6–2g per kg of body weight daily) and resistance training (lifting weights 2–4 times per week). Studies show that people who follow both practices lose primarily fat during a deficit, while those who only reduce calories without resistance training or adequate protein lose a significant proportion of muscle alongside fat.
What is TDEE and how is it different from BMR?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — just to keep your organs functioning. TDEE (Total Daily Energy Expenditure) is your actual total daily calorie burn including BMR plus all physical activity (exercise, walking, fidgeting, digestion). For most people, TDEE is 1.3–1.9× their BMR depending on activity level. TDEE is your 'maintenance calories' — the number you eat to maintain your current weight. A calorie deficit is created by eating below your TDEE.
Last updated: February 12, 2025
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Frequently Asked Questions
How do I calculate my calorie deficit?
Step 1: Calculate your BMR using Mifflin-St Jeor: Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. Women: same formula but −161 instead of +5. Step 2: Multiply BMR by your activity factor (1.2 to 1.9) to get your TDEE (maintenance calories). Step 3: Subtract 250–750 calories from your TDEE to create your deficit. Our calculator does all of this automatically in under 45 seconds.
How many calories should I eat to lose 1kg per week?
1kg of body fat stores approximately 7,700 calories. To lose 1kg per week, you need a daily deficit of 7,700 ÷ 7 = 1,100 calories. This is a large deficit — for most people it would require eating less than 1,500 calories/day, which is difficult to sustain and risks muscle loss. The standard recommendation is 0.5kg/week (500 cal/day deficit) for sustainable fat loss. Losing more than 1% of body weight per week consistently increases the risk of muscle loss significantly.
What is a good calorie deficit for weight loss?
The most evidence-based calorie deficit for sustainable weight loss is 500 calories per day below your TDEE (maintenance calories). This produces approximately 0.45kg (1 lb) of fat loss per week, is achievable without extreme dietary restriction, allows adequate protein and nutrient intake, and minimises muscle loss when protein targets are met. Larger deficits (750+ cal/day) accelerate fat loss but require more discipline and increase the risk of muscle loss and metabolic adaptation.
What should my macros be in a calorie deficit?
For optimal fat loss while preserving muscle: Protein should be 1.6–2.0g per kg of body weight (or goal weight if losing significant mass) — this is non-negotiable. Fat should be at least 0.7–1.0g per kg of body weight, minimum, to maintain hormonal health — this represents approximately 25–30% of total calories. Carbohydrates fill the remaining calories. Our calculator automatically calculates your personal macro targets based on your calorie level and body weight.
How long will it take to lose 10kg?
At a moderate 500 calorie/day deficit, you lose approximately 0.45kg of fat per week. 10kg ÷ 0.45kg/week = approximately 22 weeks (about 5.5 months). At an aggressive 750 calorie/day deficit: 10kg ÷ 0.68kg/week = approximately 15 weeks. At a mild 250 calorie/day deficit: approximately 44 weeks. Our calculator shows your personalised timeline for all three deficit levels based on your actual TDEE.
Does a calorie deficit cause muscle loss?
A calorie deficit alone does cause some muscle loss — this is unavoidable during weight loss. However, two factors dramatically minimise it: high protein intake (1.6–2g per kg of body weight daily) and resistance training (lifting weights 2–4 times per week). Studies show that people who follow both practices lose primarily fat during a deficit, while those who only reduce calories without resistance training or adequate protein lose a significant proportion of muscle alongside fat.
What is TDEE and how is it different from BMR?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — just to keep your organs functioning. TDEE (Total Daily Energy Expenditure) is your actual total daily calorie burn including BMR plus all physical activity (exercise, walking, fidgeting, digestion). For most people, TDEE is 1.3–1.9× their BMR depending on activity level. TDEE is your 'maintenance calories' — the number you eat to maintain your current weight. A calorie deficit is created by eating below your TDEE.