Calorie Deficit Calculator

How Do You Calculate Calorie Deficit?

A calorie deficit means taking in less energy than your body uses over time, so your body has to draw on stored energy to help cover the gap (British Nutrition Foundation; NHS calorie counting guidance).

Most calculators estimate your resting needs first by using the Mifflin–St Jeor equation, which predicts resting energy expenditure from your weight, height, age and sex (Mifflin et al., 1990).

• For men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5 (Mifflin et al., 1990).
• For women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161 (Mifflin et al., 1990).
• You then apply an activity multiplier to estimate your total daily energy expenditure (TDEE), which is your approximate maintenance intake.
• Finally, you subtract calories from that maintenance estimate to create a deficit for weight loss.

For many adults, a modest starting deficit of around 500 to 600 kcal per day is more practical than going as low as possible, and the NHS commonly uses a roughly 600 kcal reduction as a starting point for average adults trying to lose weight (NHS calorie counting guidance).

The British Dietetic Association says a realistic target for many adults is about 0.5 to 1 kg per week, which is roughly 1 to 2 lb per week in old money (British Dietetic Association).

It is important to treat any calculator result as a starting estimate rather than an exact prescription, because predictive equations can be noticeably off for individuals even when they perform reasonably well at group level (PMC study on predictive REE equations).

How Do I Work Out My Calorie Deficit?

Work out your own calorie deficit in three steps: estimate your BMR from your weight, height, age and sex, multiply it by an activity factor to get your maintenance calories, then subtract the deficit you want to run. The calculator at the top of this page does all three for you, but the arithmetic is simple enough to check by hand.

1. Estimate your BMR. Using Mifflin–St Jeor, a 40-year-old woman weighing 70 kg at 165 cm has a BMR of about 1,370 kcal, and a 40-year-old man weighing 85 kg at 178 cm about 1,770 kcal (Mifflin et al., 1990).
2. Multiply by your activity level to get maintenance. That same woman, lightly active, would be around 1,880 kcal a day, which is her total daily energy expenditure and roughly the amount she would eat to stay the same weight.
3. Subtract your deficit. Taking off roughly 600 kcal gives her about 1,280 kcal a day, and the NHS describes a reduction of around 600 kcal as a safe and sustainable way to lose weight (NHS calorie counting guidance).

Your deficit is the gap, not the target: eating 1,280 kcal against an 1,880 kcal maintenance level is a 600 kcal deficit, and you can create part of that gap by moving more rather than eating less.

What Is My Calorie Deficit?

Your calorie deficit is the difference between the calories you eat and the calories your body burns in a day, so there is no single number that applies to everyone, because it depends on your size, age, sex and how active you are. Enter your details in the calculator above and it will show your maintenance level alongside the deficit that each weight-loss scenario represents.

• If you already know roughly what you eat, subtract it from your maintenance estimate: someone maintaining at 2,200 kcal who eats 1,700 kcal is running a 500 kcal daily deficit.
• A deficit only counts over time, so averaging 500 kcal below maintenance across a week matters far more than any individual day, which is why one large meal rarely undoes a week of consistency.
• If you believe you are eating in a deficit but your weight has not moved in two to three weeks, the likeliest explanation is that your maintenance estimate is too high or your tracking is missing calories, rather than your body having stopped responding (study on predictive REE equations).

What Are My Maintenance Calories?

Your maintenance calories are the number you would eat to keep your weight stable, and the NHS uses UK averages of around 2,000 kcal a day for women and 2,500 kcal a day for men (NHS calorie counting guidance). Your personal figure will differ from those averages, which is exactly what the maintenance line in the calculator above estimates.

• Maintenance is your BMR multiplied by an activity factor, so two people of the same weight can differ by several hundred calories a day purely on how much they move.
• Treat the number as a starting hypothesis and test it: eat at your estimated maintenance for two to three weeks and weigh yourself regularly, then adjust by 100 to 200 kcal if your weight drifts.
• Maintenance falls as you lose weight, because a smaller body costs less to run, so the intake that produced a deficit at the start of a diet may only be maintenance by the end of it (Hall & Chow, 2013).

What Is My BMR?

Your basal metabolic rate (BMR) is the energy your body uses at complete rest just to stay alive, covering breathing, circulation, brain function and cell repair. It is the single biggest component of most people's daily energy use, and the calculator above estimates it using the Mifflin–St Jeor equation (Mifflin et al., 1990).

• The equation is 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years), then + 5 for men or − 161 for women (Mifflin et al., 1990).
• BMR is not your calorie target. It is the floor before any movement is counted, which is why eating at your BMR is a much steeper deficit than most people intend.
• Predicted BMR can be out by a few hundred calories for any given individual even though these equations perform well across groups, so use it as an estimate rather than a measurement (study on predictive REE equations).

How Do You Use BMR to Calculate a Calorie Deficit?

You do not subtract your deficit from your BMR. Multiply BMR by your activity factor first, then subtract from that, because skipping the activity step is the most common mistake and produces a target far lower than intended.

• Sedentary is roughly BMR × 1.2, lightly active × 1.375, moderately active × 1.55 and very active × 1.725.
• A woman with a 1,370 kcal BMR who is lightly active maintains at about 1,880 kcal, so a 600 kcal deficit is about 1,280 kcal a day, not 770 kcal.
• If the activity factor you pick already includes your workouts, do not then subtract your exercise calories a second time.

How Does This Calculator Work?

This calculator estimates your BMR with Mifflin–St Jeor, applies an activity factor to estimate TDEE, and then shows a maintenance level plus several weight-loss scenarios based on progressively larger deficits (Mifflin et al., 1990).

Those scenarios are useful planning ranges, not guarantees, because real-world energy needs are influenced by factors such as body composition, daily movement, medication, menstrual cycle, sleep, stress and how consistently you follow the plan (World Health Organization; PMC study on predictive REE equations).

In practice, the best target is usually the largest deficit you can sustain while still eating a balanced diet, staying reasonably active, sleeping properly and feeling in control of your eating rather than stuck in a restrict-and-rebound cycle (British Dietetic Association; Harvard T.H. Chan School of Public Health).

If your weight trend has not moved after two to three weeks of consistent tracking, you can adjust your intake or activity slightly instead of making drastic cuts straight away.

What Should My Calorie Deficit Be?

For most adults, a daily deficit of around 500 to 600 kcal is the sensible default, because it produces the 0.5 to 1 kg (1 to 2 lb) a week that the NHS describes as a safe and steady rate of loss (NHS guidance on overweight and obesity; NHS calorie counting guidance).

• Bigger is not better. NICE advises against nutritionally unbalanced restrictive diets and stresses a flexible, individualised approach, because a deficit you abandon in three weeks loses to a smaller one you hold for six months (NICE overweight and obesity management guidance (NG246)).
• Scale it to your size. A 600 kcal deficit is a modest cut for someone maintaining at 3,000 kcal and an aggressive one for someone maintaining at 1,700 kcal, so a percentage of maintenance is often a fairer guide than a flat number.
• Judge it by how you feel as well as by the scales, because persistent hunger, poor sleep, low mood, dropping training performance or creeping binges are all signs the deficit is too large (British Dietetic Association).

How Many Calories Should I Eat to Be in a Calorie Deficit?

You are in a calorie deficit as soon as you eat below your own maintenance level, so the number is personal. As a rough UK guide, the NHS Weight Loss Plan sets daily targets of 1,900 kcal for most men and 1,400 kcal for most women, which is roughly average maintenance minus 600 kcal (NHS Weight Loss Plan, week 1).

• Those figures come from average maintenance levels of 2,500 kcal for men and 2,000 kcal for women, so if you are taller, heavier or more active than average your deficit intake will be higher than 1,900 or 1,400 (NHS calorie counting guidance).
• There is no universal threshold below which everyone starts losing weight, because a 1,600 kcal day is a deficit for one person and a surplus for another.
• Very low intakes are a different thing entirely: diets providing 800 kcal a day or less should only ever be followed under close medical monitoring (NICE information for the public on special diets).

Is a 500-Calorie Deficit Safe?

For many adults, a daily deficit of around 500 to 600 kcal is a sensible and sustainable place to start, which is why the NHS uses roughly a 600 kcal reduction in its general weight-loss advice and the British Dietetic Association recommends aiming for gradual loss rather than a quick fix (NHS calorie counting guidance; British Dietetic Association).

That said, safe is personal: a deficit that feels manageable for a larger, more active person may be too aggressive for someone smaller, older, very lean or living with a medical condition, so if your intake is getting very low or your energy, mood and training are suffering, the deficit probably needs adjusting (World Health Organization; NHS calorie counting guidance).

How Do You Calculate a Calorie Deficit for Fat Loss?

The calculation is identical whether your goal is weight loss or fat loss, namely maintenance minus a deficit, but how you run the deficit changes how much of the loss comes from fat rather than muscle. A moderate deficit with enough protein and some resistance training loses a greater share of fat than an aggressive deficit alone.

• Keep protein high across the day, because protein-rich foods improve fullness and can help protect lean mass during weight loss, particularly alongside exercise (Harvard on protein, carbs and weight loss).
• Include muscle-strengthening activity on at least two days a week, on top of the 150 minutes of moderate activity the NHS recommends (NHS physical activity guidelines).
• Expect scale weight to be a noisy measure of fat loss, because water, glycogen, salt, fibre and the menstrual cycle can all move it by a kilo or more, so a weekly average and a tape measure tell you more than any single morning's reading.

How Many Calories to Lose a Stone?

A stone is 6.35 kg, and body fat stores roughly 7,700 kcal per kilogram, so losing a stone means accumulating a total deficit in the region of 49,000 kcal. At a 600 kcal daily deficit that works out to somewhere around 11 to 12 weeks, which fits the NHS guidance of 0.5 to 1 kg a week (NHS guidance on overweight and obesity).

• Treat that as an order of magnitude rather than a schedule, because the familiar 3,500 kcal per pound arithmetic reliably overestimates real weight loss by assuming your deficit stays constant while your body gets smaller (Hall, 2008; Hall & Chow, 2013).
• Progress is usually front-loaded and then slows, because maintenance falls as you lose weight, so the last few pounds of a stone typically take longer than the first few.
• If you are starting from a higher weight, a stone is a smaller share of your body mass and often comes off faster, and losing 5 to 10% of your body weight is a well-evidenced first target with real health benefits (British Dietetic Association).

How Much of a Calorie Deficit Do You Need to Lose 10kg?

Losing 10 kg requires a cumulative deficit of roughly 77,000 kcal, based on about 7,700 kcal per kilogram of body fat. Run at a 600 kcal daily deficit that is approximately 18 weeks, or about four months, and at the NHS rate of 0.5 to 1 kg a week it lands between 10 and 20 weeks (NHS guidance on overweight and obesity).

• Do not try to compress it by doubling the deficit, because larger cuts tend to increase hunger, lose more lean mass and are far harder to sustain for four months than a moderate deficit is (British Dietetic Association).
• Plan for the deficit to shrink on its own, because by the time you have lost 10 kg your maintenance may be 200 to 300 kcal lower, so the intake that started as a deficit will need revisiting.
• Simple linear projections overestimate loss over a period this long, so expect the real curve to flatten rather than run in a straight line (Hall & Chow, 2013).

If I Eat 600 Calories a Day, How Much Weight Will I Lose?

On paper, eating 600 kcal a day against an average maintenance of 2,000 to 2,500 kcal is a deficit of 1,400 to 1,900 kcal, which projects to roughly 1.3 to 1.7 kg (3 to 4 lb) a week. In practice that is two to three times the rate the NHS considers safe, and 600 kcal a day is a very low calorie diet that NICE says you should never follow unless a doctor is closely monitoring you (NHS guidance on overweight and obesity; NICE information for the public on special diets).

• Diets of 800 kcal a day or less are used in the NHS only in specific clinical situations, are not used for routine weight loss, should not run beyond 12 weeks, and come with supervision, nutritional support and follow-up to prevent regain (NICE information for the public on special diets; NHS guidance on overweight and obesity).
• The projected figure also flatters reality, because rapid loss at very low intakes includes a substantial amount of water, glycogen and lean tissue, and linear calorie arithmetic overestimates what actually happens on the scales (Hall, 2008).
• If you are drawn to 600 kcal because progress feels too slow, a 500 to 600 kcal deficit rather than a 600 kcal intake gets you 0.5 to 1 kg a week without the medical risk, and you can hold it for months (NHS calorie counting guidance). If your weight is affecting other health conditions and you need to lose weight quickly, that is a conversation to have with your GP, who can refer you to supervised support (NHS guidance on overweight and obesity).

What About 500 or 1,000 Calories a Day?

At 1,000 kcal a day most adults would be running a deficit of roughly 1,000 to 1,500 kcal, which projects to about 0.9 to 1.4 kg a week, while 500 kcal a day is more extreme than 600 and carries the same warnings.

• Both 500 and 800 kcal fall under the very low calorie threshold that requires medical supervision, and even 1,000 kcal a day is low enough that meeting your vitamin, mineral and protein needs becomes genuinely difficult (NICE information for the public on special diets).
• Use the scenarios in the calculator above to find the fastest rate you can reach with a deficit rather than a starvation intake, which for most people is a target well above 1,000 kcal.
• Speak to a healthcare professional before cutting this far, and especially if you have or have had an eating disorder (British Nutrition Foundation).

Understanding Calorie Counting

Calorie counting works because body weight is influenced by long-term energy balance, but the quality of those calories still matters for hunger, nutrition and health (British Nutrition Foundation; NHS calorie counting guidance).

That means a lower-calorie diet built around vegetables, fruit, beans, wholegrains, dairy or fortified alternatives, and protein-rich foods is usually more filling and easier to sustain than simply squeezing ultra-processed foods into a calorie target (British Nutrition Foundation; Harvard protein guidance).

It also helps to remember that obesity is not just about willpower: the World Health Organization describes it as a multifactorial, chronic relapsing disease shaped by biology, psychology and the wider food and activity environment (World Health Organization).

Calorie counting can be very useful because it teaches portion awareness and helps many people spot where extra energy is creeping in, but it is not the only effective method and it may not suit everyone, especially anyone with a current or past eating disorder (NHS calorie counting guidance; British Nutrition Foundation).

How Do You Get Into a Calorie Deficit?

Getting into a calorie deficit means either eating less, moving more, or both. The calculator gives you the number, and the habits below are how people actually hit it, with most finding it easier to cut a few reliable sources of calories than to overhaul everything at once.

• Start with liquids and extras, since alcohol, milky coffees, oils, spreads and sauces add up fast and are easy to trim without touching the volume of food on your plate (NHS calorie counting guidance).
• Build meals around filling foods such as vegetables, beans, lentils, oats, yoghurt, eggs, fish and lean poultry, so the deficit costs you less hunger per calorie (British Nutrition Foundation).
• Create part of the gap with activity, aiming for at least 150 minutes of moderate activity a week plus two muscle-strengthening sessions, which lets you eat a little more at the same rate of loss (NHS physical activity guidelines).

How to Start Calorie Counting

1. Use the calculator to get a starting calorie target, and begin with a moderate deficit rather than an aggressive one (NHS calorie counting guidance; British Dietetic Association).
2. Track what you actually eat and drink for at least a week or two, including oils, spreads, sauces, alcohol, milky coffees and small snacks, because these extras can add up quickly (NHS calorie counting guidance).
3. Weigh or measure portions at first so that your entries match what is on the label or in your tracking app (NHS calorie counting guidance).
4. When comparing packaged foods, check kcal per 100 g as well as per serving, because manufacturer portion sizes are not always realistic for the amount people actually eat (NHS food labels guidance).
5. Use front-of-pack traffic lights to compare similar products quickly, and aim for more greens and ambers and fewer reds over the course of the week (NHS food labels guidance).
6. Build meals around foods that improve fullness, such as vegetables, fruit, beans, lentils, oats, yoghurt, eggs, fish, lean poultry and other higher-protein staples (Harvard protein guidance; British Nutrition Foundation).

Tips for Effective Calorie Counting

• Pick a sustainable deficit, not the biggest one you can tolerate for a few days, because slower and steadier loss is generally easier to maintain than crash dieting (British Dietetic Association; Harvard T.H. Chan School of Public Health).
• Aim to keep protein in the plan, because protein-rich foods can improve fullness and may help preserve lean mass during weight loss, especially when paired with exercise (Harvard on protein, carbs and weight loss).
• Choose better protein sources most of the time, such as fish, beans, lentils, yoghurt, nuts and poultry, rather than relying heavily on processed meats (Harvard protein guidance).
• Include muscle-strengthening activity at least 2 days a week and aim for at least 150 minutes of moderate activity or 75 minutes of vigorous activity across the week (NHS physical activity guidelines).
• Sleep matters more than many people think, because inadequate sleep is linked with higher body weight and can make appetite regulation harder (Harvard T.H. Chan School of Public Health).
• Hydration helps too, and UK advice commonly encourages roughly 6 to 8 glasses of fluid a day as part of a healthy routine (British Nutrition Foundation).
• If tracking starts to feel obsessive or stressful, switch to a simpler approach such as portion guidance, regular meal structure or support from a registered dietitian, because calorie counting is only one tool and not the right fit for everybody (NHS calorie counting guidance; British Nutrition Foundation).

Should I Count Calories Every Day?

Not necessarily, because calorie counting is a tool rather than a rule, and the NHS explicitly says it is not the only way to lose weight (NHS calorie counting guidance).

Some people benefit from tracking daily for a few weeks so they can learn portions and spot patterns, then move to a looser approach built around repeat meals, better food choices and regular weighing; others prefer to keep tracking for longer because the structure helps them stay consistent (NHS calorie counting guidance; British Nutrition Foundation).

If tracking starts to dominate your day or damages your relationship with food, it is worth stepping back and choosing a simpler method or seeking professional support (British Nutrition Foundation).

UK Resources for Calorie Counting and Weight Loss

• NHS Better Health – Lose Weight offers the free 12-week NHS Weight Loss Plan and practical support to build healthier eating and activity habits.
• NHS Calorie Counting explains calorie targets, food diaries and portion awareness in plain English.
• NHS Food Labels is especially useful if you want to compare kcal per 100 g, portion sizes and traffic-light labels when shopping.
• British Dietetic Association – Obesity and Overweight gives evidence-based advice from dietitians on safe, realistic and sustainable weight loss.
• British Nutrition Foundation – Obesity, Healthy Weight Loss and Nutrition is a strong UK reference for energy balance, behaviour change and practical meal ideas.
• NICE overweight and obesity management guidance and the related NICE quality standard QS212 set out the evidence-based framework for prevention, behavioural management, assessment and treatment in UK health services.