Choose how fast you would like to lose weight, add a few personal details, and this tool works out a daily calorie target that creates a matching deficit without dropping below a safe minimum.
Your details stay on your device. Nothing is sent or stored.
Key points
- A calorie deficit means using more energy than you take in, so the body draws on its stores. The tool calculates your maintenance level first, then subtracts a deficit for the weekly pace you pick.
- Built-in floors: the suggested target never goes below 1,200 kcal a day for women or 1,500 kcal for men. If your chosen pace would need less, you see a warning instead.
- The maths uses a rule of thumb: about 7,700 kcal per kilogram of body weight. It is a fair guide for the first weeks but overestimates weight loss over months.
- Slower usually lasts longer. About 0.5 kg (1 lb) a week is the default because it is realistic, comfortable and easier to keep up.
- Losing 5% of your weight already brings real health benefits for many people, long before any “ideal” weight.
How does the calorie deficit calculator work?
The calculator runs three steps in a row. Knowing them helps you judge whether the result makes sense for you.
- Your resting energy use. From your sex, age, weight and height, it estimates your basal metabolic rate with the Mifflin-St Jeor equation, explained in detail on our calorie calculator page.
- Your maintenance calories. It multiplies that resting figure by your activity level (from 1.2 for mostly sitting to 1.9 for very active).
- Your daily target. It takes the pace you chose, multiplies it by 7,700 kcal per kilogram and divides by seven days. That daily deficit is subtracted from maintenance.
Finally, it compares the target with the safety floor for your sex. If the target is lower, the floor is shown together with a warning, and the daily deficit is reduced to match.
The four paces and what they mean per day
The dropdown offers four weekly paces. Each one translates into a fixed daily deficit at the start of your weight loss.
| Pace per week | Daily deficit | Who it may suit |
|---|---|---|
| 0.25 kg (0.5 lb) | about 275 kcal | People close to their goal, older adults, anyone who wants very small changes |
| 0.5 kg (1 lb) | about 550 kcal | Most adults; the default setting |
| 0.75 kg (1.5 lb) | about 825 kcal | People with a high starting weight and a high maintenance level |
| 1 kg (2 lb) | about 1,100 kcal | Only realistic for people with very high energy needs; often hits the floor |
A deficit of around 500 to 750 kcal a day is also the range used in the American guideline on managing overweight and obesity in adults. Our default sits comfortably inside it.
Reading your result
The result box shows three figures, each rounded to the nearest 10 kcal. The large one at the top is your suggested daily calorie intake.
- Suggested daily calories: the amount to aim for on an average day.
- Calories to keep your weight: your estimated maintenance level, for comparison.
- Daily deficit: the gap between the two. If the floor was applied, this gap is smaller than the pace you chose.
A highlighted warning means your chosen pace would require eating less than 1,200 or 1,500 kcal. Rather than accepting the floor, pick a slower pace: the plan will be easier to follow, and your results will likely hold up better.
Examples: the same pace, different bodies
Because the deficit is fixed per pace, the effect on your plate depends heavily on your starting point.
A woman of 52, 165 cm, 110 kg, lightly active. Her maintenance level is about 2,350 kcal. At 0.5 kg a week, her target is roughly 1,800 kcal. At 0.25 kg a week it is around 2,080 kcal, and even at 1 kg a week it stays just above the floor, at about 1,250 kcal.
A woman of 60, 160 cm, 85 kg, mostly sitting. Her maintenance level is about 1,670 kcal. A pace of 0.25 kg a week gives around 1,390 kcal. If she chooses 0.5 kg a week, the sum would come to roughly 1,120 kcal, so the calculator shows 1,200 kcal with a warning.
For her, the slower pace is the better plan. Adding a daily walk would raise her maintenance level and widen the room for food, which is often more pleasant than eating less.
Is the 7,700 kcal rule accurate?
The figure of 7,700 kcal per kilogram comes from the older “3,500 calories per pound” rule. It goes back to a 1958 paper by Max Wishnofsky, who estimated the energy stored in a pound of lost or gained body tissue.
As a description of stored energy, it is reasonable. The problem starts when it is used to forecast weight loss over months, as if the body stayed the same while it shrinks.
Why the simple rule overestimates weight loss
When you lose weight, your body needs less energy: there is less tissue to maintain and less weight to move. A deficit that was 550 kcal at the start becomes smaller every month, even if you keep eating exactly the same.
Kevin Hall and colleagues published a model in The Lancet that accounts for this. Their rough guide for adults: every lasting change of 100 kJ (about 24 kcal) a day eventually shifts body weight by about 1 kg, with half of that change reached after roughly a year and nearly all of it after about three years.
The same paper showed that the static rule can overestimate weight loss considerably once you look beyond the first months. Diana Thomas and colleagues compared the rule with carefully controlled studies and concluded that it clearly overestimates actual weight loss.
| 7,700 kcal per kg rule | Dynamic models (Hall and others) | |
|---|---|---|
| Assumes | The deficit stays the same over time | Energy needs fall as weight falls |
| Predicted weight loss | A straight line, week after week | Fast at first, then slower, then a plateau |
| Good for | Rough planning over the first weeks | Realistic long-term expectations |
| Practical lesson | Choose a pace you can sustain | Recalculate as you go and expect a plateau |
What this means for you
Our calculator uses the simple rule because it is easy to understand and works well for setting a starting point. Use it for the next few months, not for the next few years.
Recalculate after every 5 kg or so, or whenever your activity changes. When weight loss slows down or stops, that is not a sign of failure: it is the plateau the models predict.
A short checklist when progress stalls
- Recalculate with your current weight; your maintenance level is probably lower than when you started.
- Look at the last month, not the last week. Fluid shifts can hide fat loss for days at a time.
- Check portion creep. Over time, servings, snacks and drinks tend to grow without us noticing.
- Review sleep and stress. Short nights and busy weeks often raise appetite and make planning harder.
- Add movement before cutting food further. A few extra minutes of walking each day is usually easier than eating even less.
Sometimes the right decision is to stop losing for a while and practise holding your new weight. That is a valid goal, not giving up.
The body also defends its weight in other ways. Appetite tends to rise after weight loss, which is one reason our page on weight regain treats maintenance as a skill in its own right.
Is 1,200 or 1,500 calories enough? Safe floors explained
The floors in the calculator are minimums, not goals. For most people living with obesity, a healthy weight-loss intake is well above them.
The American guideline mentioned earlier describes reduced-calorie diets of roughly 1,200 to 1,500 kcal a day for women and 1,500 to 1,800 kcal a day for men, usually adjusted for body weight. We use the bottom of each range as the line the tool will not cross.
| Daily intake | What it usually means |
|---|---|
| Around maintenance minus 250–750 kcal | A moderate deficit; suitable for most adults wanting to lose weight |
| 1,200–1,500 kcal (women), 1,500–1,800 kcal (men) | Lower end of standard reduced-calorie diets; needs careful food choices to cover nutrients |
| Below 1,200 kcal (women) or 1,500 kcal (men) | Not shown by our calculator; only with guidance from a doctor or dietitian |
| About 800 kcal or less | Very low calorie diets; used only in specific cases under medical supervision |
Eating very little has real downsides. It is hard to get enough protein, fibre, vitamins and minerals, hunger can become overwhelming, and fast weight loss raises the risk of gallstones and muscle loss.
Why is slow weight loss more sustainable?
NHS advice describes losing about 0.5 to 1 kg (1 to 2 lb) a week as a safe rate for most people. Our default sits at the gentle end of that range, for good reasons.
You can keep eating normal food
A small deficit lets you keep your favourite meals, eat with family and friends, and still make progress. Plans that feel like punishment rarely survive a holiday, a stressful month or a birthday.
A large trial in the New England Journal of Medicine compared four reduced-calorie diets with different amounts of fat, protein and carbohydrate in 811 adults. After two years, weight loss was similar on all of them. What mattered was sticking to a lower intake, not the exact recipe.
You protect more muscle
Some of the weight lost during any diet is muscle and other lean tissue. A review in Advances in Nutrition describes how enough protein and regular resistance exercise help preserve muscle while you lose weight.
Muscle matters for strength, balance, blood sugar control and everyday independence: getting out of a chair, climbing stairs, carrying shopping. The macro calculator shows a protein guide for your height.
Health gains start early
You do not need to reach a “normal” BMI to feel better. The American guideline on managing overweight and obesity reports that losing 3 to 5% of body weight already improves blood sugar and blood fats, and more weight loss brings further benefits for blood pressure.
For someone weighing 110 kg, 5% is 5.5 kg. At 0.5 kg a week, that milestone can be within reach in about three months.
Limits and who should be careful
A calculator cannot see your medical history. Treat the result as a conversation starter, and check with a professional first if any of the following applies to you.
- Diabetes medicines. If you use insulin or tablets that can cause low blood sugar, eating less can lead to hypos. Your doctor may need to adjust your medication before or during a change in diet.
- Pregnancy and breastfeeding. Do not aim for a calorie deficit while pregnant. During breastfeeding, talk to your midwife, health visitor or doctor first.
- Eating disorders. If you have ever lived with an eating disorder, or notice yourself becoming preoccupied with numbers, a calorie target can do harm. Seek support before changing how you eat.
- Kidney, heart or liver disease. These can change what and how much you should eat and drink.
- Older age. Losing muscle is a bigger concern later in life. A slower pace, enough protein and strength exercise are especially important.
- Under 18. The calculator is for adults. Children and teenagers should not follow calorie deficits without specialist advice.
The figures are estimates for adults. Real energy needs vary, and a deficit that suits one person can be too large for another. If you feel dizzy, weak, very tired or constantly cold, eat more and speak to your doctor.
If weight keeps coming back despite your efforts, that is common and not your fault. Our page on obesity treatment explains what professional help can look like.
Turning your target into everyday steps
You do not need to hit your number to the calorie. Aim for an average across the week and focus on changes you can keep.
Talk to your doctor first before you change how you eat or move, especially if you live with diabetes, heart or kidney disease.
On your plate
- Start with drinks: swapping sugary soft drinks and juices for water, tea or coffee without sugar can cover a large part of a daily deficit on its own.
- Make half your plate vegetables or salad at lunch and dinner. They add volume and fibre for relatively few calories.
- Include a protein food at each meal, such as pulses, eggs, fish, yoghurt or lean meat, to help you feel full for longer.
- Plan snacks rather than grazing. A piece of fruit or a handful of nuts at a set time works better than “just a bite” all afternoon.
For a ready-made week of meals at a gentle deficit, see our free 7-day eating plan.
If you want to track your intake against your target, our guide to calorie counting shows a gentle five-step start.
On your feet
Moving more widens your deficit without taking food away. A short daily walk is the easiest place to start, and our walking plan helps you build up from a few minutes.
The free Start workouts add gentle strength exercise, which helps you keep muscle while you lose fat. They are made for people with a heavier body, sore joints or little experience.
With support
People who have regular support tend to do better than those who go it alone. You can book a free video meeting (in English) to talk about a realistic target and a plan that fits your life.
Create a free Club account to keep track of the eating plan and workouts in one place. No subscription, no cost.
Related calculators
- Calorie calculator: your BMR and maintenance calories, with the formula explained.
- Weight loss calculator: see when you might reach a goal weight at your chosen pace.
- Macro calculator: split your daily target into carbohydrate, fat, protein and fibre.
Frequently asked questions
Is 1,200 calories a day enough?
For some smaller women, 1,200 kcal can be a reasonable lower limit for a weight-loss diet, which is why our calculator uses it as a floor for women. For most people living with obesity it is far below what they need, and eating that little makes it hard to get enough protein, fibre and nutrients. Going lower should only happen under medical supervision.
Is 1,500 calories enough for a man to lose weight?
For many men, 1,500 kcal a day leads to weight loss, but it is a minimum, not a target. A larger or more active man will usually lose weight on considerably more. The calculator shows 1,500 kcal for men only when a faster pace would otherwise push the target below that level.
Why have I stopped losing weight even though I still eat the same?
As you lose weight, your body needs less energy, and it also adapts by using a little less and making you hungrier. Your original deficit therefore shrinks over time until weight loss levels off. Recalculate with your new weight, look again at movement and sleep, and remember that keeping lost weight off is already a success.
How big should my calorie deficit be?
Clinical guidelines commonly use a deficit of about 500 to 750 kcal a day for adults with overweight or obesity. In our calculator, a pace of 0.5 kg a week corresponds to about 550 kcal a day at the start. Smaller deficits also work and are often easier to live with.
Do I need to count calories to be in a deficit?
No. Many people reach a deficit by changing what is on their plate, cutting down on sugary drinks and snacks, and walking more, without tracking any numbers. The calculator is a guide to how big a change is useful, not an instruction to log every bite.
Sources
- Hall KD, et al. – Quantification of the effect of energy imbalance on bodyweight. The Lancet (2011)
- Thomas DM, Martin CK, et al. – Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. International Journal of Obesity (2013)
- Wishnofsky M – Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition (1958)
- Jensen MD, et al. – 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults. Circulation (2014)
- Sacks FM, et al. – Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. New England Journal of Medicine (2009)
- Cava E, Yeat NC, Mittendorfer B – Preserving healthy muscle during weight loss. Advances in Nutrition (2017)
- Education Authority NI Healthwell (NHS content) – Should you lose weight fast?