Calorie Calculator

This calculator estimates how much energy you burn in a day, then works backwards to the intake that would hold your weight steady or move it at a chosen rate. It runs on three published equations and an activity multiplier, and the number it returns is an estimate of an average rather than a measurement of you.

The three equations behind the answer

The Harris-Benedict Equation, published in 1919, was one of the first attempts to predict basal metabolic rate, the energy a body spends at complete rest. Roza and Shizgal revised it in 1984, and that version held until the Mifflin-St Jeor Equation arrived in 1990. Mifflin-St Jeor also predicts BMR and has tested more accurate than the revised Harris-Benedict across most populations.

The Katch-McArdle Formula works differently. It predicts resting daily energy expenditure from lean body mass, which means it needs a body fat percentage and neither of the other two equations uses that. Muscle burns more at rest than fat does, so an equation that knows how much of you is muscle can beat one that only knows your total weight.

Mifflin-St Jeor is the sensible default. Katch-McArdle beats it for lean people who have had their body fat measured properly.

Mifflin-St Jeor Equation

Men: BMR = 10W + 6.25H - 5A + 5
Women: BMR = 10W + 6.25H - 5A - 161

Revised Harris-Benedict Equation

Men: BMR = 13.397W + 4.799H - 5.677A + 88.362
Women: BMR = 9.247W + 3.098H - 4.330A + 447.593

Katch-McArdle Formula

BMR = 370 + 21.6(1 - F)W

where:

• W is body weight in kilograms
• H is body height in centimetres
• A is age in years
• F is body fat as a decimal, so 20% goes in as 0.20

Take a 25-year-old man, 5 feet 10 inches and 165 pounds. That is 74.84 kg and 177.8 cm. Mifflin-St Jeor gives 748.4 + 1,111.25 - 125 + 5, or 1,740 calories at rest. Revised Harris-Benedict gives 1,802 for the same person, and Katch-McArdle at 20% body fat gives 1,663. A 139-calorie spread between equations for one identical body is the honest measure of how precise any of this is.

From resting burn to a daily target

BMR only covers what a body spends lying still. Standing up, walking to the kitchen, typing and fidgeting all cost more, and so does training. The calculator multiplies BMR by an activity factor to cover the rest of the day.

Activity level	Factor
Basal Metabolic Rate, at rest all day	1.0
Sedentary: little or no exercise	1.2
Light: exercise 1-3 times a week	1.375
Moderate: exercise 4-5 times a week	1.465
Active: daily exercise, or intense exercise 3-4 times a week	1.55
Very active: intense exercise 6-7 times a week	1.725
Extra active: very intense exercise daily, or a physical job	1.9

Exercise here means 15 to 30 minutes with your heart rate up. Intense exercise means 45 to 120 minutes. Very intense means two hours or more. Our example man at the moderate factor lands at 1,740 x 1.465, or about 2,549 calories a day to stay where he is.

Most people overestimate their own activity level. A gym session three times a week alongside a desk job and a car commute is light or moderate, not active. If the number the calculator gives you does not match what you actually eat while your weight holds steady, the activity factor is usually the reason.

The 3,500 calorie rule

A pound of body fat holds roughly 3,500 calories, and 0.45 kg holds about the same. Run a 500-calorie daily gap and the week comes to 3,500, which is a pound. Our example man eating 2,049 instead of 2,549 would be down about a pound a week on paper.

Goal	Rate	Daily change
Maintain weight	steady	0
Mild weight loss	0.5 lb (0.25 kg) a week	-250
Weight loss	1 lb (0.5 kg) a week	-500
Extreme weight loss	2 lb (1 kg) a week	-1,000
Mild weight gain	0.5 lb (0.25 kg) a week	+250
Weight gain	1 lb (0.5 kg) a week	+500

The rule is a useful approximation and it degrades over months. As you get lighter you burn less, so the same intake that once produced a deficit eventually becomes maintenance. Recalculate every 10 to 15 pounds rather than trusting one number for a year.

How far down is too far

Cutting intake by more than 1,000 calories a day is a bad trade. Losing more than 2 pounds a week usually costs muscle, and less muscle means a lower BMR, so the metabolism you are trying to work with gets smaller. Rapid drops on the scale are also often water rather than fat, and dehydration is not progress.

Harvard Health Publications puts the floor at 1,200 calories a day for women and 1,500 for men without medical supervision. Below that the body prioritises survival over everything else, and the functions it drops first are the ones that make you feel well: immune response, hormone production, concentration, mood, sleep quality.

Diet and exercise together remain the approach with the most evidence behind it. Training while eating in a deficit protects muscle, which protects BMR, which is what keeps the deficit working.

Zigzag calorie cycling

Hold a flat deficit long enough and the body adapts to it. Non-exercise movement drops, hormones shift, and weight loss stalls at a plateau that a further cut only makes worse. Zigzag cycling is one way around that: vary intake day to day while keeping the week the same.

Suppose your target is 14,000 calories a week. You could eat 2,000 every day, or 2,300 on three days and 1,775 on the other four. The week is identical either way, but the second version never gives the body a stable low number to settle against.

The practical benefit is scheduling. A wedding, a birthday dinner or a Sunday roast stops being a failure and becomes a high day you planned for, paid for with lower days either side. Nothing gets eaten in secret and no week gets written off.

No study fixes the ideal spread. A gap of 200 to 300 calories between high and low days suits most people, with the high day usually sitting at maintenance. More active people can carry a wider gap. The calculator draws a week with two higher days and five lower ones, all adding to the same total as a flat 1 lb a week loss.

Whether you count flat or zigzag matters less than whether you can keep doing it in March. Pick the version that survives contact with your actual life.

How many calories do you need?

It depends on your size, your age, your sex, how much you move, and a set of individual factors nobody has fully mapped. Two people matched on every measurable variable can still differ by a few hundred calories a day.

A physically active 25-year-old man at 6 feet needs far more than a sedentary 70-year-old woman at 5 feet. The US Department of Health puts adult men at roughly 2,000 to 3,000 calories a day to maintain weight, and adult women at 1,600 to 2,400. Those bands are wide because the honest answer is a range.

Survival takes surprisingly little. Living well takes more. Eat too little for too long and the body keeps the lights on while quietly switching off everything it can afford to lose, which is why a very low intake can leave you thinner and worse off at the same time.

Calories: different kinds and their effects

Carbohydrate, protein and fat supply nearly all the energy in a normal diet, with alcohol a significant fourth for many people. Alcohol carries close to 7 calories a gram and almost no nutrition alongside them.

Studies keep finding gaps between the calories printed on a label and the calories a body actually keeps. Chewing is part of it. Chewing more raises the energy spent on digestion, and it slows the meal down enough for satiety to arrive before the plate is empty. Foods that demand chewing, such as fruit, vegetables, lean meat and whole grains, cost more to process and keep you full longer. Coffee, tea, chilli, cinnamon and ginger all nudge the burn rate up slightly through the compounds they contain.

Quality matters alongside quantity. High-calorie foods pack a lot of energy into a small serving, and that is a description rather than a criticism: avocados, nuts, quinoa and whole grains are all calorie-dense and worth eating. Low-calorie foods carry less energy per serving, which is most vegetables and many fruits. Empty calories, mostly added sugar and solid fat, bring energy and almost nothing else.

Five hundred calories of carrots and 500 calories of popcorn do not land the same way. Carrots take real chewing, cost more to digest, and keep you full. The mechanism is not fully mapped, and calories in against calories out still governs the direction of travel, but the number on the label is not the number your body banks.

Drinks are worth watching on their own. They make up an estimated 21% of a typical person's intake, and much of that is empty. Fizzy drinks are the obvious offender, but juice and milk carry real sugar too. Water, tea and coffee without sugar are the cheapest calories to remove from a day.

Nothing here makes any food off limits. Fruit contains a lot of sugar. Reduced-fat products often replace the fat with sugar to rescue the flavour. Read what is actually in a product rather than what the front of the packet claims about it.

Calories in common foods

Food	Serving	Calories	kJ
Apple	1 (4 oz)	59	247
Banana	1 (6 oz)	151	632
Grapes	1 cup	100	419
Orange	1 (4 oz)	53	222
Pear	1 (5 oz)	82	343
Strawberry	1 cup	53	222
Watermelon	1 cup	50	209
Broccoli	1 cup	45	188
Carrots	1 cup	50	209
Lettuce	1 cup	5	21
Tomato	1 cup	22	92
Beef, cooked	2 oz	142	595
Chicken, cooked	2 oz	136	569
Tofu	4 oz	86	360
Egg	1 large	78	327
Shrimp, cooked	2 oz	56	234
Bread, white	1 slice (1 oz)	75	314
Butter	1 tablespoon	102	427
Caesar salad	3 cups	481	2,014
Cheeseburger	1 sandwich	285	1,193
Pizza	1 slice (14 in)	285	1,193
Rice	1 cup cooked	206	862
Beer	1 can	154	645
Coca-Cola Classic	1 can	150	628
Diet Coke	1 can	0	0
Milk (whole)	1 cup	146	611
Orange juice	1 cup	111	465
Yogurt (low-fat)	1 cup	154	645

One cup is about 250 millilitres and one tablespoon is about 14.2 grams.

Sample days at 1,200, 1,500 and 2,000 calories

Meal	1,200 plan	1,500 plan	2,000 plan
Breakfast	Bran cereal (125), milk (50), banana (90)	Granola (120), Greek yogurt (120), blueberries (40)	Buttered toast (150), egg (80), banana (90), almonds (170)
Snack	Cucumber (30), avocado dip (50)	Orange (70)	Greek yogurt (120), blueberries (40)
Lunch	Grilled cheese with tomato (300), salad (50)	Chicken and vegetable soup (300), bread (100)	Grilled chicken (225), grilled vegetables (125), pasta (185)
Snack	Walnuts (100)	Apple (75), peanut butter (75)	Hummus (50), carrots (35), crackers (65)
Dinner	Grilled chicken (200), sprouts (100), quinoa (105)	Steak (375), mashed potato (150), asparagus (75)	Salmon (225), brown rice (175), green beans (100), walnuts (165)

These are illustrations of portion size rather than prescriptions. Anyone eating at 1,200 for an extended period should be doing it with medical advice.

Calories burned by common exercise

Activity, one hour	125 lb	155 lb	185 lb
Golf, using a cart	198	246	294
Walking, 3.5 mph	215	267	319
Kayaking	283	352	420
Softball or baseball	289	359	428
Basketball, general	340	422	503
Swimming, freestyle moderate	397	492	587
Tennis, general	397	492	587
Soccer, general	397	492	587
Football, general	399	494	588
Bicycling, 12-14 mph	454	562	671
Running, 9 minute mile	624	773	923

Heavier bodies burn more for the same work, which is why the columns climb from left to right. An hour of running burns roughly what a cheeseburger and a can of Coke supply, and that comparison is the reason diet usually beats exercise as a lever for weight loss.

Energy in the components of food

Component	kJ per gram	Calories per gram	Calories per ounce
Fat	37	8.8	249
Ethanol (drinking alcohol)	29	6.9	196
Protein	17	4.1	116
Carbohydrate	17	4.1	116
Organic acids	13	3.1	88
Polyols (sugar alcohols)	10	2.4	68
Fibre	8	1.9	54

Labels round these to the Atwater figures of 9, 4 and 4 for fat, protein and carbohydrate. Fat carries more than twice what protein or carbohydrate does per gram, which is why a spoonful of oil moves a total further than a plate of vegetables.

Calories, calories and kilojoules

The word calorie does two jobs, and the difference is a factor of a thousand. A small calorie, written cal, is the energy that raises one gram of water by one degree Celsius. A large Calorie, written kcal and usually capitalised on packaging, is a thousand of those. Every food label in the United States uses the large one, so a 250-calorie bar is really 250,000 small calories.

Most of the world labels food in kilojoules instead. One large Calorie is 4.1868 kJ under the international steam table definition, which is what the converter here uses. The thermochemical definition puts it at 4.184 kJ, and EU labelling rules use that figure. The gap is under a tenth of a percent and only shows up in the last digit of a large number.

Kilojoules = Calories x 4.1868
Calories = kilojoules / 4.1868

A 2,000 Calorie day is about 8,374 kJ. An 8,700 kJ day, the reference figure on Australian labels, is about 2,078 Calories.

Reading the number on the packet

Two figures usually appear on a label: per 100 grams and per serving. The per-serving figure is the one that misleads, because the manufacturer chooses the serving. A bag of crisps listing 150 calories may hold two and a half servings, and a tub of ice cream can run to four. Compare products on the per-100-gram column and portions on the pack you are actually going to eat.

US regulations allow a tolerance of up to 20% above the stated value, and restaurant meals drift further still because kitchens are not laboratories. Cooked weight adds another wrinkle: 100 grams of dry pasta becomes around 250 grams cooked, and the calories belong to the dry weight. Weighing rice or pasta after boiling is one of the most common counting errors there is.

Where the calories actually go

Daily burn breaks into four parts, and only one of them happens in a gym.

Basal metabolic rate is the largest by a distance, usually 60% to 70% of the total for someone who is not an athlete. It pays for the heart, the brain, the kidneys and the constant work of staying alive. The brain alone takes around a fifth of it.

The thermic effect of food is roughly 10%, the energy spent digesting and storing what you eat. It varies by macronutrient, and the spread is larger than most people expect: protein costs 20% to 30% of its own calories to process, carbohydrate 5% to 10%, fat almost nothing at 0% to 3%. Eating 100 calories of chicken nets you closer to 75.

Exercise activity is the part everyone thinks about and it is usually the smallest, often 5% to 10% for a person who trains a few times a week. An hour of moderate cycling for a 155 lb person is 562 calories, which is one large muffin and a latte.

Non-exercise activity thermogenesis, or NEAT, covers walking, standing, fidgeting, carrying shopping and pacing on the phone. It varies enormously between people, by as much as 2,000 calories a day between a desk worker who drives everywhere and a postal worker on foot. NEAT is also the part that quietly falls when you cut intake, which is a large piece of why long deficits stall.

Protein, fullness and keeping the muscle you have

Two people eating the same deficit can lose very different amounts of muscle, and protein intake explains much of the gap. A 2018 meta-analysis by Morton and colleagues put the useful ceiling for muscle retention and growth at around 1.6 grams per kilogram of body weight a day, with little further benefit above that. For an 80 kg person that is roughly 128 grams.

Protein also does more per calorie for appetite than the other macronutrients. It costs the most to digest, empties from the stomach slowly, and shifts the hormones that signal fullness. A breakfast built around eggs or Greek yogurt tends to shorten the gap to lunch compared with the same calories from toast and juice.

Fibre works in a similar direction through bulk rather than chemistry. Vegetables, legumes, fruit and whole grains fill the stomach at a low calorie cost, which makes a deficit easier to hold without thinking about it constantly.

Counting without weighing everything

Logging every gram works, and most people stop doing it within a month. Several lighter approaches get close enough.

Weigh and log for two weeks only, then stop. That is long enough to learn what 500 calories looks like on a plate, which is the actual skill. Most people are shocked by cooking oil and by nut portions, and unbothered by the vegetables they were worried about.

Log the three or four items that carry most of your intake and estimate the rest. Bread, oil, cheese, alcohol and anything ordered from a menu usually account for the bulk of the error. Salad leaves never do.

Or skip counting and change the structure instead: protein at every meal, vegetables at two, drinks without sugar, and a fixed number of meals a day. This produces a deficit for many people without a single number being written down.

Self-reported intake is routinely under-recorded by 20% to 30% in research settings, and that gap is nearly always honest rather than deliberate. Forgotten oil, unlogged tastes while cooking and generous portion estimates cover most of it. If the scale is not moving on a target you believe you are hitting, the intake estimate is a more likely culprit than a slow metabolism.

Why the scale disagrees with the maths

Body weight moves for reasons that have nothing to do with fat. Glycogen binds about three grams of water for every gram stored, so a carbohydrate-heavy weekend can add two or three pounds overnight and lose them again by midweek. Sodium shifts fluid the same way. So does the menstrual cycle, a hard training session, poor sleep and constipation.

The fix is measurement discipline rather than a better equation. Weigh at the same time each day, after the bathroom and before eating, and judge the seven-day average against the previous seven-day average. A daily reading tells you almost nothing. A fortnight of averages tells you whether the target is right.

Expect the first week of any deficit to overstate progress and the second to look like nothing happened. Both are water, in opposite directions, sitting on top of a fat loss that is roughly linear underneath.

What this calculator cannot tell you

Every equation here was fitted to a population, and you are one person. Predicted BMR typically lands within about 10% of a measured value, which on a 2,500-calorie day is a 250-calorie band. Thyroid conditions, medication, pregnancy, recent large weight changes and unusual body composition all push the answer further off.

Treat the number as a starting point. Eat at it for two or three weeks, weigh yourself under the same conditions each time, and adjust based on what the scale did rather than what the equation predicted. The calculator gets you to a sensible first guess in seconds; your own data settles the rest.

Anyone who is pregnant or breastfeeding, under 18, managing diabetes or an eating disorder, or working around a chronic condition should get a target from a clinician instead. The equations above were never fitted to those situations.