How Many Calories Do You Need a Day? (Real Numbers, Goal by Goal)

The short answer

Two numbers produce your daily calorie need. The first is your basal metabolic rate, or BMR: the energy your body burns at complete rest just to keep your heart beating, your lungs breathing, your cells turning over and your brain running. The second is an activity multiplier that scales that resting figure up to what you actually do in a day. Multiply the two and the result is your total daily energy expenditure, TDEE — the number of calories that keeps your weight exactly where it is.

For the resting part, the standard open equation is the Mifflin-St Jeor formula, which takes your sex, age, height in centimetres and weight in kilograms. It is what the calculator linked at the bottom of this page uses, and it is the equation most dietitians reach for because it needs no body-composition measurement to be useful. Then the activity multiplier — 1.2 if you are sedentary, up to 1.9 if you train twice a day — does the rest. Roughly speaking, most adult women land somewhere between 1,800 and 2,400 kcal/day and most adult men between 2,200 and 3,000 kcal/day, but that spread is wide enough to be nearly useless on its own, which is the entire reason the equation exists.

• To find your number: BMR from Mifflin-St Jeor, times your activity multiplier, equals TDEE.
• TDEE is maintenance. Eat it and your weight holds.
• Add or subtract about 500 kcal/day and you move roughly one pound a week.
• Any figure from an equation is a population estimate — expect to adjust it with real data.

What your body actually spends energy on

It helps to know what you are calculating, because the biggest component surprises most people. For a normally active adult, resting metabolism typically accounts for the majority of the day's energy — often somewhere around 60 to 75 percent — long before any exercise enters the picture. Running burns fewer calories than people imagine; being alive at all burns a lot more than they imagine. This is why a calorie target built on exercise alone fails, and why a target built on BMR multiplied by a realistic day works.

The remaining energy splits into three buckets. Physical activity is the obvious one, both deliberate exercise and the walking, standing, stairs and carrying that fill a day. Food itself costs energy to digest, absorb and store — usually around 10 percent of what you eat, which is one reason severe restriction lowers your total spend. And there is fidgeting, posture and spontaneous movement, the stuff no tracker labels as exercise, which varies enormously between two people with identical desk jobs and is a real part of why individual needs differ so much from any formula's prediction.

The equation: Mifflin-St Jeor

The two versions differ by one term at the end, and that single term is worth 166 kcal/day. Everything before it is identical. Enter weight in kilograms, height in centimetres and age in years.

Mifflin-St Jeor is the equation most practitioners default to for adults, and it is what the calculator linked at the bottom of this page uses, because it needs only four inputs that anyone knows about themselves. Older formulas ask for the same inputs but assume a different body composition, and the original Harris-Benedict equation tends to return a higher resting figure than Mifflin-St Jeor for many people, since it was derived from a much smaller and differently built sample a century ago. The catch with any of them is that they predict an average: individual resting metabolism can sit noticeably above or below the figure, which is why the number you get is a starting point to test rather than a dose to obey.

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

A worked example, start to finish

Take a 30-year-old woman who is 165 cm tall, weighs 62 kg and exercises three to five times a week. Her resting metabolic rate is 10 × 62 = 620, plus 6.25 × 165 = 1,031.25, minus 5 × 30 = 150, minus 161. Adding those up: 620 + 1,031.25 = 1,651.25, minus 150 = 1,501.25, minus 161 = 1,340.25 kcal. So her body would burn roughly 1,340 kcal if she lay still for 24 hours.

Then apply the activity multiplier for moderate activity, which is 1.55: 1,340.25 × 1.55 = 2,077.4, so about 2,077 kcal/day is her maintenance estimate. That is the whole calculation. From here, 1,577 kcal/day would be a 500 kcal deficit aimed at losing roughly a pound a week, and 2,577 would be a 500 kcal surplus — and both of those are starting points to be tested, not verdicts.

Metric in, imperial on the page

The equation only accepts metric units, so if you know your height in feet and inches and your weight in pounds, convert first: 1 lb is about 0.4536 kg and 1 in is 2.54 cm. Someone 5 ft 4 in and 137 lb is 162.6 cm and 62.1 kg. The calculator linked below accepts either unit system directly, so you never have to do that arithmetic by hand, and it applies the same sex term the formula requires.

Picking your activity multiplier honestly

This is the step where the estimate goes wrong most often, because people pick the level they aspire to rather than the level they live. The multiplier is the difference between 1,800 and 2,800 kcal/day on the same body, so a wishful choice here is not a small error. Judge yourself on the last two weeks, not on your best week.

A useful sanity check: a sedentary adult with a desk job, no planned exercise and a car for transport is genuinely ×1.2, and that describes most office workers. Two or three short gym sessions a week plus a desk job is light, not moderate. Only someone training nearly every day with a physically demanding job or two-a-day sessions belongs at the top two levels.

• Sedentary — desk job, little planned exercise: multiply BMR by 1.2.
• Light — exercise 1–3 days per week: multiply by 1.375.
• Moderate — exercise 3–5 days per week: multiply by 1.55.
• Very active — hard exercise 6–7 days per week: multiply by 1.725.
• Extra active — physical labour plus intensive training: multiply by 1.9.

The number for each goal

Once you have a maintenance estimate, every goal is the same arithmetic with a different sign. The anchor is the rough rule of thumb that a pound of body fat stores about 3,500 kcal — roughly 7,700 kcal per kilogram — so a daily gap of 500 kcal should move you about one pound a week. It is a rule of thumb and it deserves to be treated as one: real bodies change water and glycogen alongside fat, they adapt their spending as you change, and the rate you get is rarely exactly the rate you planned.

So work from your own TDEE, not from a number copied off someone else's plan, and change one thing at a time. The cases below all use the same example body from the previous section — a 30-year-old woman, 165 cm, 62 kg, moderately active, maintenance around 2,077 kcal/day — so you can substitute your own figure and get the same shape of answer. Each case also notes where the estimate stops being the authority and a clinician should be.

To maintain my weight

Eat your TDEE. In the worked example that is around 2,077 kcal/day. Maintenance is not the absence of a plan; it is the reference point every other target is measured from, and it is worth holding for a week or two and checking whether your weight actually holds before you set a deficit or a surplus. If your weight drifts at your calculated TDEE, your real expenditure differs from the prediction, and the number needs adjusting — that drift is information, not failure.

Practically, maintenance is the safest place to start if you have never tracked before. Establish what your body does at a known intake, then move from there.

To lose weight

A deficit of about 500 kcal/day below your TDEE is the standard, gentle target, and it corresponds to roughly one pound a week. Continuing the example: 2,077 − 500 = about 1,577 kcal/day. If you want a slower, easier route, a 250 kcal deficit gives about half a pound a week and is far more likely to be sustainable for months than an aggressive cut is.

The common mistake is stacking two deficits at once — cutting food hard and adding a lot of training — which compounds into fatigue, hunger and a much lower chance of still doing it in eight weeks. Prefer the smallest deficit that produces progress you can keep. And a floor matters: a target that lands below roughly 1,600 kcal/day for a woman or 1,800 for a man usually needs professional supervision rather than willpower, because getting adequate protein, fibre, vitamins and minerals from a very small intake becomes genuinely difficult.

To gain weight

A surplus of about 300 to 500 kcal/day above TDEE is the usual recommendation, because beyond that the extra tends to go to fat rather than to tissue you wanted. On the example figure of 2,077, that is a target around 2,380 to 2,580 kcal/day. Expect the scale to move about 0.25 to 0.5 kg per week; if it is not moving after two or three weeks, add another 150 to 200 kcal and reassess.

The practical difficulty is appetite, not arithmetic. Surpluses are easier to hit with calorie-dense foods — oils, nuts, nut butters, dairy, grains cooked rather than diluted — and by adding food rather than replacing it, so a smoothie or a second dish is layered onto normal meals instead of squeezing them smaller.

To gain muscle

Muscle gain needs a surplus, but a modest one, and it needs a stimulus: without resistance training, extra calories become mass of a different kind. So the target is TDEE plus roughly 250 to 500 kcal, with protein treated as the constraint that actually limits the outcome. A widely used intake target during a muscle-building phase is around 1.6 g of protein per kg of body weight per day, spread across meals, with the remaining calories divided between carbohydrate to fuel training and fat for hormonal and general health. On the example body — 62 kg, TDEE 2,077 — that is roughly 100 g of protein a day inside a target of about 2,330 to 2,580 kcal.

Expect slower scale movement than a pure 'gain weight' plan calls for, because useful muscle accrues at a fraction of the rate that fat does, especially once you are past the beginner stage. If the scale climbs much faster than about 0.5 kg a week, the surplus is too large. New lifters and returning lifters gain faster than trained ones, so set expectations accordingly.

While breastfeeding

Making milk costs energy, and the additional figure that is widely cited for the first six months of full breastfeeding is roughly 300 to 500 kcal per day on top of your normal requirement. So a woman whose calculated maintenance is 2,077 kcal would be somewhere around 2,380 to 2,580 kcal/day while nursing. Food can supply part of that and stored body fat the rest, which is why many people lose pregnancy weight gradually while breastfeeding without a formal diet — but a deliberate deficit during lactation is a bad idea, both for milk supply and for nutrient status.

This is one of the cases where the equation is a starting point and a clinician is the authority. Individual needs vary with how much milk you produce, how often you feed or pump, your own stores and your diet quality. If you are breastfeeding, pregnant, or managing a medical condition or medication, treat every number in this guide as a rough frame and confirm the target with your doctor, midwife, or a registered dietitian rather than self-managing it.

For women and for men: why the numbers differ

At identical age, height and weight, the Mifflin-St Jeor result for a man is 166 kcal/day higher than for a woman, because the formula adds 5 in one case and subtracts 161 in the other. That term is the formula's crude way of accounting for the average difference in body composition: men on average carry more lean mass and less fat mass for the same weight, and lean tissue is the metabolically expensive part.

In practice the gap between typical women and typical men is much larger than 166 kcal, and that is mostly size and activity rather than sex — men are usually taller and heavier, which drives the weight and height terms, and they more often report higher activity levels. The honest reading: do not use a friend's number because you share a sex. Run the equation with your own measurements. If you are comparing the two, the difference you see will come overwhelmingly from your own height, weight and how you move, not from the constant at the end of the line.

How many calories do you need to survive?

This search usually means one of two things, and both deserve a straight answer. Taken literally, survival is not a clean calorie threshold: it depends on starting body fat, water, climate, activity and health, and people with large stores can survive far longer than those without — which is precisely why there is no safe number to aim at. What matters for anyone eating real meals is that survival is the wrong target. The question worth asking is the minimum intake at which you stay healthy, functional and nourished.

Taken as 'how low can I go', the practical answer is that the low-calibre diets popular online sit well below what most adults need, and they are not something to self-manage. Below roughly 1,000 to 1,200 kcal/day, hitting adequate protein, iron, calcium, B vitamins, fibre and essential fats becomes very difficult without medical oversight and often without supplementation. Known consequences include muscle loss, fatigue, hair loss, cold intolerance, missed periods, gallstones and a metabolism that drops to match the lower intake — followed by a high rate of regained weight when the diet ends.

So use the deficit guidance above, not a survival figure. If you are already eating very little and still not losing, that is a signal to stop and see a professional rather than to cut further. And if you are underweight, have lost weight without trying, or have any history of disordered eating, an individualised plan with qualified support is the only sensible route — no calculator on this page substitutes for that.

Using a calorie calculator instead of doing it by hand

The arithmetic is simple but tedious, and the two places people slip are unit conversion and activity selection. A calculator removes the first entirely. The Calorie & TDEE Calculator here takes sex, age, height and weight — height in centimetres or feet and inches, weight in kilograms or pounds — plus your activity level, and it uses the Mifflin-St Jeor equations above. It returns your resting metabolic rate, the activity-adjusted total daily energy expenditure, a target for the goal you pick, and a protein, carbohydrate and fat split for that target, so the macro question answers itself alongside the calorie question.

It runs entirely in your browser, which matters more here than it does for most tools: your age, height and weight are body measurements many people would rather not have sitting on a server, and nothing is transmitted anywhere. The page just does the maths on your device.

One related measurement worth having in context is body mass index, which describes where your weight sits relative to your height rather than what you should eat. The BMI Calculator on this site gives the score under both the WHO classification and the Asia-Pacific classification — the two use different cut-off points, so the category can differ depending on which standard you read — and it accepts metric or imperial units too. BMI and calorie needs are separate questions: BMI is a population screening band, calorie needs are an energy estimate, and neither is a diagnosis.

Why your real number will drift, and how to correct it

Every equation here predicts a population average, and the published error bands on resting metabolic predictions are on the order of 10 percent — which on a 2,000 kcal target means being off by 200 kcal/day in either direction is entirely normal, not a malfunction. Taller-than-average builds, more or less lean mass than the formula assumes, thyroid differences, sleep, and medications all shift the true value. Treat the output as a first hypothesis.

Test it: hold your target steady for two to three weeks, weigh yourself at the same time each morning, and compare the weekly average rather than any single day. Weight bounces daily with water, sodium, carbohydrate storage and where you are in your cycle, so a single reading tells you nothing while a weekly trend tells you a lot. If maintenance intake leaves your weight climbing, your real TDEE is lower than predicted and you drop 100 to 200 kcal. If a deficit produces no change in the weekly average after three weeks, raise intake slightly and increase activity rather than cutting further — and if you are pregnant, breastfeeding, on medication that affects weight, or managing a condition such as diabetes or thyroid disease, the drift is exactly the kind of thing to take to a clinician instead of tuning alone.

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