Calorie Calculator

What Is a Calorie?

A calorie is a unit of energy: the energy it takes to raise the temperature of one gram of water by one degree Celsius. The calorie printed on a food label is a thousand of those — a kilocalorie — and it measures the chemical energy your body can extract from what you eat. Nothing about the unit is specific to food or to bodies; it is an energy measure that happens to be convenient for both sides of the ledger.

That single fact explains why one number can describe both a plate of pasta and a morning of sitting at a desk. Energy in and energy out are quoted in the same unit, so they can be subtracted from one another — which is the entire premise of this calculator and of every diet built on one.

Calorie, kilocalorie, kilojoule

Three labels for the same quantity cause most of the confusion here. In ordinary English a "calorie" on a menu is a kilocalorie, written kcal on packaging. The NHS notes that calorie information is given in kcals — short for kilocalories — and in kJ, short for kilojoules, which is the metric energy unit used alongside it on European labels.

One kilocalorie is 4.184 kilojoules, so the conversion is a single multiplication. The 2,556 kcal this calculator returns for its reference man is 10,694 kJ. If your food diary reports kilojoules and your calculator reports calories, dividing the kilojoules by 4.184 puts them back on the same scale before you compare them.

Everything on this page is in kilocalories per day and is written simply as calories, because that is what the label on the food will say.

Where the calories in food come from

Only four components of food carry energy, and each carries a different amount per gram. The Food and Agriculture Organization publishes the Atwater general factors used on nutrition labels worldwide:

The arithmetic on any label follows directly. A meal of 30 g protein, 60 g carbohydrate and 20 g fat is 120 + 240 + 180 = 540 kcal, and no other information about the food changes that total. Fat carries more than twice the energy of the same weight of protein or carbohydrate, which is why two plates of identical size can differ by several hundred calories.

Water, fiber that passes undigested, vitamins and minerals contribute nothing to the total. That is why a large volume of vegetables costs so little against a daily target, and why a small handful of nuts costs so much.

To split your daily total into grams of protein, carbohydrate and fat, take the number into the Macro Calculator.

What "daily calorie needs" actually means

Your daily calorie need is total daily energy expenditure: resting metabolism, plus the cost of digesting food, plus every movement you make, deliberate or not. Resting metabolism is the largest piece and the only one this calculator estimates directly. Everything else is covered by the multiplier you choose.

The multiplier tells you how the split works out. At the Sedentary factor of 1.2, resting burn is 83 percent of the day's total; at Moderate it is 65 percent; at Very Active it is 53 percent. Even for someone training six days a week, more than half the calories go on staying alive rather than on the training.

That is the honest reason a calorie target is worth calculating rather than guessing. The bulk of the number is fixed by your body, not by your gym schedule, and it barely moves from day to day.

How Do You Calculate Your Daily Calories?

Two steps. First estimate the calories you burn at complete rest with the Mifflin-St Jeor equation, then multiply that by an activity factor. The calculator does both and shows you the product; the sections below show the working, so you can reproduce any number on this page by hand.

The formula, written out

Mifflin-St Jeor estimates basal metabolic rate from weight in kilograms, height in centimeters and age in years. The two versions differ only in the constant at the end, and the second line is the whole of what the activity factor does:

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

Daily calories = BMR × activity factor (1.2, 1.375, 1.55, 1.725 or 1.9)

BMR is basal metabolic rate — the calories your body spends at complete rest keeping organs, temperature and cell repair running. Nothing else is going on inside this calculator: it evaluates one of those two lines, multiplies by the factor you picked, and rounds to a whole calorie.

In the original 1990 paper the two equations above are a simplification of one combined regression, REE = 9.99 × weight + 6.25 × height − 4.92 × age + 166 × sex − 161, where sex is 1 for men and 0 for women. The authors reported that rounding the coefficients and splitting the equation by sex did not affect its predictive value, which is why the tidy version is the one every calculator uses.

If you enter pounds or inches, the calculator converts first — 0.453592 kg per pound, 2.54 cm per inch — and then applies the metric equation. There is no separate imperial formula.

Step by step

• Select your sex. It changes only the constant at the end of the equation: +5 for men, −161 for women.
• Enter your age in whole years. Every year subtracts 5 calories from BMR before the multiplier is applied.
• Pick your weight unit, then enter your weight. Ten calories of BMR ride on each kilogram.
• Pick your height unit, then enter your height. Feet.inches means 5.10 for 5 ft 10 in — the digits after the point are whole inches.
• Choose the activity level that matches a typical week, not your best week. This is the field that moves the answer most.
• Read the result. It is one number: the calories per day at which your weight should hold steady.

There is no goal selector on this page. The calculator returns maintenance only, and every target — losing, gaining, holding — is that number plus or minus an offset you apply yourself, using the table further down.

Worked example: 30-year-old man, 70 kg, 175 cm, Moderate

The reference case used throughout this page. Weight and height go in as metric, so nothing is converted.

BMR = 10 × 70 + 6.25 × 175 − 5 × 30 + 5
BMR = 700 + 1,093.75 − 150 + 5 = 1,648.75 kcal/day

Daily calories = 1,648.75 × 1.55 = 2,555.5625

Result returned by this calculator

2,556 kcal/day

The output is rounded to a whole calorie, so 2,555.5625 is displayed as 2,556. Working it out by hand and stopping at 2,555 is not a mistake in the arithmetic, only in the rounding.

Worked example: 154 lb at 5 ft 10 in, Moderate

The same age and activity level, entered in pounds and feet.inches. Both values are converted before the equation sees them.

154 lb × 0.453592 = 69.853 kg
5.10 → 5 ft 10 in → 70 in × 2.54 = 177.8 cm

BMR = 10 × 69.853 + 6.25 × 177.8 − 5 × 30 + 5 = 1,664.78
Daily calories = 1,664.78 × 1.55 = 2,580.4

Result returned by this calculator

2,580 kcal/day

Entering the same body as 70 in with the inch unit gives the identical 2,580. Entering it as 70 kg and 175 cm gives 2,556, because 154 lb is 69.85 kg and 5 ft 10 in is 177.8 cm — the metric round numbers describe a very slightly different person.

What each input is worth

Because the equation is linear, every field has a fixed price that you can carry in your head. At the Moderate multiplier of 1.55:

• One kilogram of body weight is worth 15.5 calories a day. Ten kilograms is 155, which is why the estimate has to be re-run as you lose.
• One centimeter of height is worth 9.7 calories a day. Rounding your height up by an inch flatters the result by about 25.
• One year of age is worth 7.75 calories, so a decade is 77.5. A 20-year-old man at 70 kg and 175 cm gets 2,633; the same body at 70 years old gets 2,246.
• Sex is worth 257 calories at this multiplier, from the 166-calorie gap between the two constants. Two 30-year-olds at 70 kg and 175 cm get 2,556 and 2,298 — a gap of 258 once both are rounded.
• One step on the activity ladder is worth 288 calories — more than any of the above, and the only input that is a judgment rather than a measurement.

Those prices scale with the multiplier you chose. At Sedentary a kilogram is worth 12 calories and a decade 60; at Very Active the same kilogram is worth 19 and the decade 95.

Activity Multipliers: 1.2 to 1.9

The activity level is the only field on the form that asks for an opinion, and it carries more weight than any measurement you take. The five options and what each is worth for the reference man — 30 years old, 70 kg, 175 cm, BMR 1,648.75:

One rung is worth 288 calories

The gap between adjacent options is 288 or 289 calories for the reference man and a flat 231 for the reference woman at 60 kg and 165 cm. Two people with identical bodies who disagree about one word on that list will walk away with targets nearly 300 calories apart — roughly a chicken sandwich a day, every day, with nothing on a food label to reveal the error.

The mistake runs in one direction. A desk job plus a daily walk is Light, not Moderate. Three gym sessions a week around a seated job is Moderate, not Active. Active means hard training almost every day; Very Active is for people who train hard and also work on their feet. If you are genuinely between two options, take the lower one — it is easier to add calories to a plan that is working than to explain a plan that has stalled.

How this ladder compares with measured activity levels

The 1.2-to-1.9 ladder is the convention that fitness tools have settled on, not an official classification, and it is worth knowing how it lines up against the research scale. Physical activity level, or PAL, is defined as total energy expenditure divided by basal expenditure — structurally the same ratio this calculator applies — and the FAO/WHO/UNU expert consultation groups adult lifestyles into three bands by it.

Two things fall out of that comparison. The Sedentary option at 1.2 sits below the bottom of the FAO's lowest band, so it describes a genuinely inactive day rather than an ordinary one. And the label Moderate here is not the FAO's "moderately active" — at 1.55 it lands inside their sedentary-to-light band. There is no official mapping between the two scales, so treat this as a sanity check on the word you picked, not a conversion table.

For scale on the research side: Brooks and colleagues, reporting the Institute of Medicine's work from doubly labeled water studies, found that 66 percent of adults holding a body mass index in the healthy range had PAL values above 1.6 — the equivalent of at least 60 minutes of moderate activity a day. The World Health Organization's floor for adults is lower, at least 150 minutes of moderate-intensity activity a week, which averages about 20 minutes a day and belongs at the Light end of this form rather than the Moderate one.

If you want to price a specific session rather than guess at a week, work it out with the Calories Burned Calculator.

Calorie Chart: Daily Needs by Age, Sex and Activity

Every figure in these tables came out of this calculator. Find the row closest to your weight, read across to your activity column, then adjust for age using the third table — 77.5 calories per decade at the Moderate multiplier. All values are kilocalories per day at maintenance.

Men, 30 years old, 175 cm tall:

Women's chart

Women, 30 years old, 165 cm tall. The whole table sits lower than the men's for two reasons at once: the −161 constant, and the smaller reference height.

Notice how far the Sedentary column falls. A 30-year-old woman of 60 kg who does not train has a maintenance of 1,584 calories, which leaves almost no room for a 500-calorie deficit without dropping under the level anyone should eat at unsupervised. That is a real constraint, not a failure of the calculator, and it is the reason the activity column matters more for smaller people than for larger ones.

What another decade costs

Age enters the equation as a flat 5 calories of BMR per year, so its effect on the final figure depends only on your multiplier: 77.5 calories per decade at Moderate, 60 at Sedentary, 95 at Very Active. Both reference bodies at the Moderate setting:

Fifty years of aging removes 387.5 calories a day at this multiplier — less than two steps on the activity ladder, which are worth 577 together, and about the same as 25 kg of body weight. The equation treats age as a proxy for the lean tissue people tend to lose over time, so if you have kept training through those decades it will read low for you, and if you stopped it will read high.

How these compare with the published averages

The NHS gives 2,500 kcal a day as an average man's requirement and 2,000 kcal as an average woman's. Those two figures are population averages, and this chart shows where they actually land on individuals. For a 30-year-old man at 70 kg and 175 cm, 2,500 sits between Light (2,267) and Moderate (2,556) — so the familiar 2,500 assumes a man who trains a few times a week, not one at a desk. For a 30-year-old woman at 60 kg and 165 cm, 2,000 is within 46 calories of the Moderate figure of 2,046 and 416 above her Sedentary maintenance of 1,584.

Reference bodies for the imperial charts you may have seen elsewhere behave the same way. A 30-year-old man of 154 lb at 5 ft 10 in returns 1,998 at Sedentary and 2,580 at Moderate; a 30-year-old woman of 126 lb at 5 ft 4 in returns 1,532 and 1,979. The average is a reasonable description of a group and a poor description of anybody in it, which is the whole argument for entering your own numbers.

How to Read Your Result

The calculator returns one figure and no breakdown: your maintenance level in calories per day. It is not a target, a limit, or a recommendation. It is the line at which your weight should sit still, and every goal is an offset from it.

Turning maintenance into a goal

A pound of body tissue is conventionally treated as about 3,500 calories, a figure that traces back to Wishnofsky in 1958. Spread across seven days that is 500 calories a day per pound a week, and MedlinePlus states the rule in the same terms: eat 500 fewer calories every day and you should lose about a pound (454 g) a week. Applied to the reference man's 2,556:

The offset has to come off your own number, never a borrowed one. The same 500-calorie subtraction is a comfortable 2,056 for the reference man, 1,279 for a 45-year-old woman of 68 kg at 160 cm doing light exercise, and 1,084 for a sedentary 30-year-old woman of 60 kg — a figure below the level anyone should eat at without supervision.

To set a rate first and let the target follow from it, with low-intake flags built in, use the Calorie Deficit Calculator.

The floors this calculator does not enforce

This page prints no dietary warnings. It will happily hand a small, sedentary adult a maintenance figure of 1,584, and if you subtract 500 from it yourself you arrive at 1,084 with nothing on screen to object. The conventional floors for dieting without medical supervision are about 1,200 calories a day for women and 1,500 for men, and they exist because protein, fiber, calcium, iron and the fat needed to absorb vitamins A, D, E and K all have to fit inside the budget.

Where the arithmetic collides with the floor, the fix is a smaller offset rather than a smaller intake. For that sedentary woman, cutting 250 instead of 500 gives a target of 1,334 and a projected 0.5 lb a week against 1.0 — half a pound of pace surrendered for a plan she can actually eat on. The other fix is to raise the left-hand side of the subtraction: moving from Sedentary to Light lifts her maintenance from 1,584 to 1,815, and the same 500-calorie cut then lands at 1,315.

Check the estimate against your own scale

The result is a prediction, and you can test it in about three weeks. Eat at the number, weigh yourself under the same conditions each morning, and compare weekly averages rather than individual readings — a single morning is mostly water, sodium and gut contents. If the weekly average is flat, the estimate was right for you. If it drifted, adjust by the drift: half a kilogram a week of unwanted loss is roughly 500 calories a day the estimate got wrong.

Re-run the calculator after about 5 kg of change, because your maintenance falls as you get smaller. A lightly active 40-year-old man of 100 kg at 180 cm has a maintenance of 2,654; at 95 kg it is 2,585, at 90 kg 2,516, and at 80 kg 2,379. Someone who set a target of 2,154 at the start — a clean 500-calorie deficit — is running a 362-calorie deficit by 90 kg and a 225-calorie deficit by 80 kg, without having changed a thing about how they eat.

Nothing has gone wrong when that happens, and nothing about the calculator has broken. There is simply less of you to run than there was, and the number has to be recomputed to say so.

How Accurate Is This Estimate?

Accurate enough to plan from, not accurate enough to argue with your scale about. Here is what is actually known about the equation, and what its published error band looks like once it reaches your screen.

What the validation evidence says

The equation comes from a 1990 paper in the American Journal of Clinical Nutrition. Mifflin, St Jeor and colleagues measured resting energy expenditure by indirect calorimetry in 498 healthy adults — 247 women and 251 men, aged 19 to 78, of whom 264 were normal weight and 234 obese — and fitted weight, height and age against it. The regression explained 71 percent of the variance between people. In the same dataset the Harris-Benedict equations of 1919 overestimated measured expenditure by 5 percent, which is why the newer equation displaced them.

A 2005 systematic review by Frankenfield, Roth-Yousey and Compher compared the four equations then in clinical use — Harris-Benedict, Mifflin-St Jeor, Owen and WHO/FAO/UNU — and concluded that Mifflin-St Jeor was the most reliable, predicting resting metabolic rate within 10 percent of measured values in more nonobese and obese individuals than any other equation. The same review is explicit that noteworthy errors and limitations exist when it is applied to individuals, and notes that older adults and ethnic minorities were underrepresented in the studies behind all four equations.

Read together, those two findings are the honest position: this is the best of the widely used estimates, and it is still an estimate built for populations and applied to a person.

What 10 percent looks like on your number

Carrying that 10 percent band through the reference calculation is the quickest way to see how much precision the single figure implies:

BMR 1,648.75 − 10% = 1,483.9  →  × 1.55 = 2,300
BMR 1,648.75 + 10% = 1,813.6  →  × 1.55 = 2,811

So the reference man's 2,556 is really somewhere between about 2,300 and 2,811 calories a day. That band is 511 calories wide — wider than the 288-calorie step between two activity levels, and about the same as choosing Light instead of Active. Anyone quoting a maintenance figure to the calorie is quoting the arithmetic, not their metabolism.

This is an argument for using the number and then correcting it, not for distrusting it. Three weeks of weigh-ins narrow that 511-calorie band far more effectively than any equation can, because they measure you rather than people who resemble you.

Where it reads high and where it reads low

The equation has no way of knowing what your weight is made of, and that is its main structural weakness. The same 1990 paper found that fat-free mass was the best single predictor of resting expenditure, on its own explaining 64 percent of the variance:

Resting expenditure = 19.7 × fat-free mass (kg) + 413

Muscle costs more to maintain than fat does, so at identical weight, height, age and sex this calculator returns one number for a lean, muscular body and the same number for a body carrying considerably more fat. It will tend to read low for the first and high for the second. A very muscular person who finds the estimate leaves them hungry and losing weight is not misreading the tool; the tool is missing the one variable that would have told it.

For an estimate of what your weight is actually made of, take a tape measure to the Body Fat Calculator.

Limits: When This Calculator Does Not Apply

One equation and one multiplication cover a lot of ground, and it is worth being specific about where they stop. Nothing here is medical advice, and the calculator cannot tell which of the following describes you.

What the calculator does not know

• Your body composition. There is no body-fat, waist or lean-mass input, so two people of the same size, age and sex always get the same answer.
• Whether the activity level you chose is true. It takes the word at face value, and one wrong word is worth 288 calories a day for the reference man.
• Your goal. It returns maintenance only — there is no lose, maintain or gain selector, and no target is generated for you.
• Any floor on intake. It prints no low-calorie warning, because it never sees the offset you intend to apply to its result.
• Anything about food. Two people eating the identical calorie total can differ completely in protein, fiber and how much muscle they keep.
• That you have lost weight since last time. The estimate is a snapshot at the weight you typed; re-run it every 5 kg.

It is also fixed to Mifflin-St Jeor. If you want to compare equations — Harris-Benedict, the revised Harris-Benedict, Katch-McArdle with a body-fat input, or Schofield — that choice lives on the TDEE page rather than this one.

To run the same body through five different resting-metabolism equations, use the TDEE Calculator.

Entry mistakes that quietly change the answer

Most of these return a plausible-looking number rather than an error, which is what makes them worth checking before you trust a result; only a blank box is refused outright. All figures are for a 30-year-old man at the Moderate setting:

• Typing 5.1 instead of 5.10 for 5 ft 10 in. The digits after the point are whole inches, so 5.1 means 5 ft 1 in: 2,361 instead of 2,583. Single-digit inches are safe either way — 5.4 and 5.04 both mean 5 ft 4 in — and anything above .11 is capped at 11 inches, so 5.12 and 5.99 both return 5 ft 11 in.
• Leaving a box empty, or typing a zero into it. A blank required box is no longer read as zero: the calculator stops before the equation runs and shows an amber notice naming the field, such as "Enter a value for Weight." Age, weight and height are all required here, and if more than one is blank the notice lists them together. A typed 0 is a different case — it is a real entry, it reaches the equation, and the equation carries no guard against it, so with age 30, height 175 cm and Moderate selected a weight of 0 returns 1,471, a height of 0 returns 860 and an age of 0 returns 2,788.
• Entering pounds with the kg unit still selected. 154 with kg chosen describes a 154 kg person and returns 3,858 instead of 2,553.
• Entering centimeters with the inch unit selected. 175 read as inches is 444 cm, and the result is 5,166.

A quick sanity check catches the ones that do get through: an adult maintenance figure between roughly 1,300 and 3,700 is plausible, and anything outside that range almost always means a unit picker or a typed zero, not an unusual metabolism.

Who should not plan from this number

• Anyone pregnant or breastfeeding. Both add energy requirements rather than subtract them, and the figures belong to a clinician working from current guidance.
• Children and teenagers. The equation was fitted on adults aged 19 to 78, and a growing body's needs are not an adult maintenance line.
• Anyone with a history of disordered eating, for whom a daily calorie number and a daily weigh-in can do more harm than the weight itself.
• People managing diabetes, thyroid disease, or kidney or liver conditions, and anyone on medication with a food-timing component — the estimate interacts with the treatment.
• Athletes and heavily muscled lifters, for whom an equation with no lean-mass term will usually read low.

For everyone else it does the job it was built for: it converts four facts about your body into a defensible starting number, which you then correct against three weeks of your own data. That correction is the part that makes it yours.