Most adults need to eat 300–500 calories below their total daily energy expenditure to lose fat at a sustainable pace. That figure is well-supported by research and the underlying formula is consistent for everyone. But the specific calorie number the formula produces? That part is not one-size-fits-all. Your body weight, age, muscle mass, activity level, and hormonal profile all shape what your personal target looks like, and understanding why that is the case is what separates a calorie target that actually works from one that stalls after three weeks.
This article walks you through the calculation, explains the variables that make your number unique, and gives you practical guidance on how to apply it and adjust it over time.
What Is a Calorie Deficit and Why Does It Drive Fat Loss?
A calorie deficit occurs when you consume fewer calories than your body burns across a given day. When that happens consistently, your body draws on stored energy, primarily body fat, to make up the shortfall. This is the fundamental mechanism behind fat loss, regardless of which dietary approach is being used.
The underlying arithmetic is straightforward. One kilogram of body fat stores approximately 7,700 calories of energy. A consistent daily deficit of 500 calories would, in theory, produce roughly 0.5 kg of fat loss per week. Over time, that compounds into meaningful change.
That said, fat loss is not purely linear. Metabolic adaptation, water retention, shifts in muscle mass, and individual physiological variation all affect the pace and pattern of real-world results. The formula is a reliable starting point, not a guaranteed output, and treating it as such is part of using it effectively.
Step One: Calculate Your Total Daily Energy Expenditure (TDEE)
Your Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns across a full day, accounting for everything from breathing and digestion to structured exercise and incidental movement. It is the number you need before any calorie target for fat loss makes sense.
TDEE is calculated in two stages.
Stage 1: Estimate Your Basal Metabolic Rate (BMR)
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest, simply to keep you alive. It accounts for approximately 60–75% of total daily energy expenditure and is driven primarily by body weight, height, age, and sex.
The Revised Harris-Benedict equation (Roza and Shizgal, 1984) is one of the most widely used formulas for estimating BMR and remains a standard reference in clinical and applied nutrition settings:
For women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)
For men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)
Stage 2: Apply an Activity Multiplier
Once you have your BMR, multiply it by an activity factor to estimate your full TDEE:
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk-based work, minimal exercise | 1.2 |
| Lightly Active | Light exercise 1–3 days per week | 1.375 |
| Moderately Active | Moderate exercise 3–5 days per week | 1.55 |
| Very Active | Hard training 6–7 days per week | 1.725 |
| Extra Active | Physical job plus daily structured training | 1.9 |
The result is your estimated TDEE: the approximate number of calories required to maintain your current weight. To create a deficit for fat loss, subtract 300–500 calories from this figure. A 300-calorie deficit produces slower, more conservative fat loss. A 500-calorie deficit accelerates results while remaining within the sustainable range recommended by most dietetic guidelines, including those from the National Health and Medical Research Council (NHMRC).
Why Your Calorie Target Is Not the Same as Everyone Else’s
Here is where most standard calorie guidance falls short. The formula above applies universally. The number it produces does not.
Several factors mean that two people of identical weight, height, and age can have meaningfully different calorie needs and therefore different targets for fat loss. Understanding these variables is what makes the difference between a target that works and one that needs constant revision.
Body Composition
Muscle tissue is metabolically active. Fat tissue, largely, is not. Two people who weigh 75 kg but carry different amounts of muscle and fat will have different resting metabolic rates and different TDEEs. The person with more lean mass burns more calories at rest, which means their maintenance intake and therefore their fat loss target will be higher.
This is one of the reasons resistance training during a calorie deficit is consistently recommended in the scientific literature. Preserving or building muscle mass keeps your metabolic rate higher and improves the quality of fat loss over time, meaning more of what you lose comes from fat rather than muscle.
Non-Exercise Activity Thermogenesis (NEAT)
Your activity multiplier accounts for structured exercise, but a significant portion of daily energy expenditure comes from something less visible: Non-Exercise Activity Thermogenesis, or NEAT. This covers the calories burned through all movement that is not deliberate exercise, such as walking, standing, fidgeting, and household tasks.
NEAT varies enormously between individuals. Research published in Science by Levine and colleagues (1999) found that NEAT differences between people could account for up to 2,000 calories per day. Two people who both sit at a desk for eight hours but move differently through the rest of their day can have vastly different TDEEs, even if every other variable is the same.
Hormonal Factors
Hormones including thyroid hormones, insulin, leptin, and cortisol all influence metabolic rate, appetite regulation, and fat storage. Conditions such as hypothyroidism or polycystic ovarian syndrome (PCOS) can meaningfully reduce metabolic rate or affect how the body processes and stores energy, making standard calorie calculations less accurate for some individuals.
If you have been genuinely consistent with your calorie target for three or more weeks and seen no change in body weight at all, a conversation with a GP or accredited practising dietitian is worth having. A calculation is not a diagnosis.
Dieting History and Metabolic Adaptation
The body responds to a sustained calorie deficit by gradually reducing its energy expenditure, a process called metabolic adaptation. Research led by Dr Rudy Leibel at Columbia University demonstrated this effect clearly, and it was further highlighted in a follow-up study of The Biggest Loser participants published in Obesity (2016), which showed that contestants experienced significant reductions in resting metabolic rate that persisted years after the show (Fothergill et al., 2016).
In practice, someone who has spent years cycling through calorie-restricted diets may have a resting metabolic rate that sits below what the formula predicts. Their calorie target needs to account for this, and may need to start more conservatively than the standard formula suggests.
This is not a permanent state, and it does not mean results are impossible. It means the starting calculation is a hypothesis to be tested and refined, not a fixed prescription to follow indefinitely.
How Protein Fits Into Your Calorie Target
Reaching a calorie target is the primary driver of fat loss, but the composition of those calories matters too, particularly protein.
Research consistently shows that higher protein intake during a calorie deficit helps preserve lean muscle mass, supports better satiety, and slightly increases the thermic effect of food (the calories burned through the process of digestion and absorption). The current evidence base supports a daily protein target of 1.6–2.2 g per kilogram of body weight when eating in a deficit, as summarised in a meta-analysis published in the British Journal of Sports Medicine (Morton et al., 2018).
For a person weighing 70 kg, that translates to approximately 112–154 g of protein per day. Reaching that target within your calorie budget requires some planning, but it meaningfully improves the quality of fat loss. You lose proportionally more fat and less muscle compared to a lower-protein approach at the same calorie intake.
Apps like INCHECK FIT are built around this principle, generating personalised meal plans that automatically hit both calorie and protein targets for each user without requiring them to do the calculations manually.
Practical Tips for Using Your Calorie Target Effectively
Knowing your number is only useful if you can apply it consistently. These principles make that considerably more achievable in practice.
Use weekly averages, not daily perfection. A daily target of 1,600 calories equals 11,200 calories per week. Whether you hit exactly 1,600 every day or vary between 1,350 and 1,900 across the week matters far less than the weekly total. This flexibility is well-supported by research and makes consistency significantly more achievable for most people.
Do not rely on exercise calorie burns to offset intake. Fitness trackers and gym equipment consistently overestimate calorie expenditure during exercise. A 2017 study from Stanford University found overestimation errors of 20–93% depending on the device and activity type (Shcherbina et al., 2017). Your TDEE already accounts for your activity level; treating structured exercise as a separate calorie bank tends to undermine progress rather than support it.
Build meals around protein first. Protein is the most satiating macronutrient. Anchoring each meal to a protein source before filling in carbohydrates and fats makes it considerably easier to stay within your calorie target without persistent hunger.
Expect the number to need adjusting. No formula is perfectly accurate for any individual. If you have been consistently hitting your calorie target for three or more weeks with no change in body weight, reducing your intake by 100–150 calories and reassessing over the following two to three weeks is the appropriate response. The target is a starting point, not a permanent prescription.
How to Know When Your Calorie Target Needs Adjusting
Calorie targets are not static. These are the clearest signals that a change is needed.
No movement on the scale after three weeks. If you have been genuinely consistent and the scale has not shifted at all, your actual TDEE is likely lower than calculated. Reduce intake by 100–200 calories and monitor for another two to three weeks before drawing conclusions.
Constant hunger or persistent fatigue. A deficit that is too aggressive, typically more than 750–1,000 calories below your TDEE, can cause significant hunger, mood disruption, and accelerated muscle breakdown. If this describes your experience, your target is probably too low. A smaller deficit applied consistently over a longer period produces better fat loss outcomes than an aggressive deficit that proves unsustainable within weeks.
Losing weight faster than 1 kg per week. If you are not significantly overweight and are losing weight rapidly, you may be losing muscle alongside fat. Reducing the deficit slightly and ensuring your protein target is being met will help preserve lean mass and improve the long-term quality of your results.
In each of these scenarios, the approach is the same: collect two to three weeks of honest data, make one measured adjustment, and assess the outcome. Changing multiple variables simultaneously makes it impossible to know what is actually driving the result.
Frequently Asked Questions
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How many calories should I eat a day to lose fat? Most adults benefit from eating 300–500 calories below their Total Daily Energy Expenditure (TDEE) to lose fat at a sustainable rate. This typically produces 0.3–0.5 kg of fat loss per week. Your specific number depends on your weight, height, age, sex, activity level, and body composition, which is why two people can have very different calorie targets even if they appear to share similar stats.
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Is 1,200 calories enough to lose weight? For some individuals, 1,200 calories may represent a reasonable fat loss target. For others, particularly those who are taller, more active, or have more lean mass, 1,200 calories would constitute an extreme deficit that is difficult to sustain and risks significant muscle loss alongside fat. Rather than starting from a fixed number, calculate your TDEE first and subtract a deficit from there to arrive at a target that is appropriate for your body specifically.
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Does everyone need the same number of calories to lose weight? No. While the formula used to calculate a calorie target is consistent, the number it produces varies significantly between individuals. Body composition, age, hormonal status, dieting history, and NEAT levels all influence what a person’s TDEE actually is and therefore what their fat loss target should be. Two people of identical height and weight can have calorie needs that differ by several hundred calories per day.
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Why am I not losing weight even though I am in a calorie deficit? The most common explanations include underestimating calorie intake (portion sizes are frequently misjudged without precise tracking), overestimating daily energy expenditure, metabolic adaptation from extended periods of prior dieting, or a TDEE that was initially overestimated. If you have been genuinely consistent with your target for three or more weeks with no measurable change, reducing your intake by 100–200 calories and reassessing is a sensible next step before drawing conclusions.
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How many calories do I need to lose 0.5 kg a week? A deficit of approximately 500 calories per day produces roughly 0.5 kg of fat loss per week, based on the established estimate that one kilogram of body fat stores approximately 7,700 calories of energy. In practice, weekly results will vary due to water retention, hormonal fluctuations, and measurement timing, so it is more useful to assess progress over two to three week periods rather than day to day.
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Should I eat the same calories every day? Not necessarily. What matters most is your total weekly calorie intake, not perfect daily consistency. Many people find it more sustainable to vary their intake slightly across the week, eating a little more on more active days and a little less on sedentary ones, while keeping the weekly total on target. The research supports this flexibility: daily precision is not required for results.
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What happens if I eat too few calories? Consistently eating well below your calorie needs, typically more than 1,000 calories below your TDEE, leads to accelerated muscle breakdown, significant fatigue, hormonal disruption, and reduced metabolic rate over time. It also tends to result in a rebound increase in food intake. A moderate deficit applied consistently over time produces considerably better fat loss outcomes than an aggressive deficit that proves unsustainable within weeks.
References
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Roza AM, Shizgal HM. “The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass.” American Journal of Clinical Nutrition. 1984;40(1):168–182. PMID: 6741850
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Levine JA, Eberhardt NL, Jensen MD. “Role of nonexercise activity thermogenesis in resistance to fat gain in humans.” Science. 1999;283(5399):212–214. PMID: 9880251
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Fothergill E, Guo J, Howard L, Kerns JC, Abumrad NN, Apovian C, et al. “Persistent metabolic adaptation 6 years after ‘The Biggest Loser’ competition.” Obesity. 2016;24(8):1612–1619. PMID: 27136388
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Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, et al. “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. 2018;52(6):376–384. PMID: 28698222
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Shcherbina A, Mattsson CM, Waggott D, Salisbury H, Christle JW, Hastie T, Wheeler MT, Ashley EA. “Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort.” Journal of Personalised Medicine. 2017;7(2):3. PMID: 28538708
Last reviewed: March 2026 by the INCHECK FIT nutrition team.
Last reviewed: March 2026
