Calorie Calculator

Which equation is running here

This page uses Mifflin-St Jeor, not Harris-Benedict. The two give noticeably different answers for the same person, so it is worth knowing which one produced a figure before comparing it with another site.

Written out, basal metabolic rate in kilocalories per day is: 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age in years, then plus 5 if you selected male or minus 161 if you selected female.

Imperial entries are converted before the equation runs. Feet and inches are combined into total inches and multiplied by 2.54 for centimetres, and pounds are multiplied by 0.45359237 for kilograms.

The five activity multipliers, spelled out

Total daily energy expenditure is simply BMR multiplied by one of five fixed factors. Sedentary is 1.2, lightly active is 1.375, moderately active is 1.55, very active is 1.725 and extra active is 1.9. Nothing else is adjusted when you change the dropdown.

That single choice moves the result more than anything else on the page, which is why guessing high is the most common way to end up with a number that does not match reality.

Worked example

A woman aged 34, 165 centimetres tall, weighing 68 kilograms, set to moderately active.

BMR = (10 x 68) + (6.25 x 165) - (5 x 34) - 161 = 680 + 1031.25 - 170 - 161 = 1380.25, displayed as 1380 kcal per day.

TDEE = 1380.25 x 1.55 = 2139.4, displayed as 2139 kcal per day.

The reference table then shows the same TDEE with flat offsets applied: 1889 for a mild deficit, 1639 for a moderate deficit, 2139 for maintenance, 2389 and 2639 for the two surpluses. Those rows are arithmetic, not a recommendation for anybody.

Now change nothing except the activity dropdown. Sedentary gives 1656 and very active gives 2381. Same body, same equation, a spread of 725 kcal a day driven entirely by a category you picked by feel.

How much trust to place in the figure

Predictive equations were built by fitting a line through measurements taken from groups of people. They describe the average of a group well and any individual only approximately. For a given person the estimate can be out by a few hundred kilocalories a day in either direction.

Things the equation cannot see include your body composition, since two people of identical height, weight, age and sex but different muscle mass share one predicted BMR. It also cannot see thyroid function or other medical conditions, medication effects, how much you fidget and move outside of planned exercise, or recent dieting history, which can lower resting expenditure.

The activity multiplier adds a second layer of approximation on top of the first. A desk job with three gym sessions is not a precise 1.55; that number is a convention.

Treat the output as an opening estimate to test against reality over several weeks, not a target to obey. This page is general information, not nutritional or medical advice. Anyone with a health condition, an eating disorder history, or who is pregnant or breastfeeding should be working with a doctor or an accredited dietitian rather than a web form.

Other ZillaKit tools that pair with this

For the weight-to-height ratio rather than an energy figure, use the BMI Calculator, which shares the same unit conversions. If you need your age in exact years before entering it, the Age Calculator works it out from a birth date. To move between pounds, stones and kilograms, try the Unit Converter.

Frequently asked

Why does this give a different number from other calculators?

Usually because the other site uses Harris-Benedict, applies a different set of activity multipliers, or adjusts for lean body mass using a body fat percentage. Comparing across equations is not meaningful unless both are named.

Should I eat my BMR figure?

The BMR card is what your body would use lying still all day, before any movement at all. It is not an eating target and treating it as one is a common misreading. Any decision about intake belongs with a qualified professional.

Which activity level should I choose?

Most people who work at a desk and train a few times a week fall between 1.375 and 1.55. If you are unsure, pick the lower of the two options you are weighing up, because self-reported activity tends to run optimistic.

Does the calculator account for the calories burned during exercise?

Only through the multiplier. There is no field for individual workouts, and adding exercise calories on top of a TDEE that already includes an activity factor would count the same effort twice.

Is my personal information going anywhere?

No. The whole calculation happens inside the page, and nothing you type is transmitted, saved or shared.