Calorie Calculator

About Calorie Calculator

Daily calorie needs are estimated in two steps. First an equation predicts your basal metabolic rate (BMR), the energy you burn lying still. Then an activity multiplier turns that into total daily energy expenditure (TDEE). This calculator offers three BMR equations (Mifflin-St Jeor, revised Harris-Benedict and Katch-McArdle), then shows intake targets from 1,000 kcal below to 500 kcal above TDEE and a carbohydrate, protein and fat split.

The weakest link is not the BMR equation. The three equations usually land within about 100 kcal of each other, but picking an activity level one notch too high adds 300 kcal or more.

Where the three equations come from

The Harris-Benedict equation was published by J. Arthur Harris and Francis G. Benedict of the Carnegie Institution of Washington in 1918, with the full monograph in 1919. It was a regression of basal metabolism, measured by indirect calorimetry in 239 adults, on weight, height and age. The version in this calculator is the 1984 re-derivation by Roza and Shizgal, who added Benedict's later subjects and refitted the coefficients (men: 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age). They reported a precision of about ±14% in normally nourished people and found it unreliable in malnourished patients.

The Mifflin-St Jeor equation came from the University of Nevada School of Medicine in 1990. The team measured resting energy expenditure in 498 healthy people aged 19 to 78, 264 of normal weight and 234 with obesity. The simplified equations are 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, and the same with −161 for women. In their sample the 1919 Harris-Benedict equations overestimated measured values by 5%, a hint that a formula built on 1910s bodies drifts when applied to heavier, less active modern populations.

Katch-McArdle (370 + 21.6 × lean body mass) drops sex, age and height and uses fat-free mass alone, because muscle and organs account for most resting energy use. The same idea shows up elsewhere: Cunningham's 1980 reanalysis of the Harris-Benedict data found lean body mass to be the single best predictor (500 + 22 × LBM), and Mifflin's paper reported 19.7 × FFM + 413.

Which equation to trust

A 2005 systematic review by Frankenfield and colleagues for the American Dietetic Association compared the four equations most used in practice: Harris-Benedict, Mifflin-St Jeor, Owen and WHO/FAO/UNU. Mifflin-St Jeor predicted resting metabolic rate within 10% of the measured value in more people, obese or not, than any other, and had the narrowest error range. The authors still warned of noteworthy individual errors, and noted that older adults and US ethnic minorities were underrepresented in both the development and validation studies.

That is why Mifflin-St Jeor is the default here. Katch-McArdle is worth a look if you know your body fat reasonably well and your muscle mass is far from average. Keep in mind that a body-fat figure from a tape or BMI estimate carries its own error, and that error flows straight into the Katch-McArdle result.

The trouble with activity multipliers

The multipliers used here are 1.2 (sedentary), 1.375 (light exercise), 1.55 (moderate), 1.725 (hard) and 1.9 (very hard plus physical work). They are the de facto standard across fitness apps, but they are a convention rather than values measured in a particular study. For comparison, the 2001 FAO/WHO/UNU expert report classed physical activity level (TDEE divided by BMR) as 1.40–1.69 for sedentary or light lifestyles, 1.70–1.99 for active and 2.00–2.40 for vigorous. The calculator's 1.2 sits below that sedentary range.

The common error is choosing by workout count alone. Three one-hour gym sessions a week do not make you very active if the other 165 hours are spent at a desk or on a couch. If you log food and weight, two or three weeks of data will tell you your true maintenance intake better than any multiplier.

Targets and the weekly weight estimate

The goal table subtracts 1,000, 500 or 250 kcal a day from TDEE, or adds 250 or 500. The predicted weekly change divides by 7,700 kcal per kilogram (the metric version of 3,500 kcal per pound), so a 500 kcal daily deficit shows as roughly 0.45 kg a week, displayed as 0.5. Treat that as a first-few-weeks estimate. As you lose weight, your BMR and the cost of moving your body fall, so the same deficit produces slower loss over time. Our guide on BMR and TDEE formulas goes into why the 3,500-calorie rule overpredicts.

Targets under 1,500 kcal for men or 1,200 kcal for women are flagged. These are conventional floors for unsupervised dieting; below them it becomes hard to meet protein and micronutrient needs.

The macro split

Macros are percentages of the target, converted to grams at 4 kcal/g for carbohydrate and protein and 9 kcal/g for fat. Presets are balanced (50/20/30), high protein (40/30/30), low carb (20/35/45) and keto (5/25/70). Percentage-based splits have one drawback: when calories drop, protein grams drop with them. If you are cutting, check protein against a grams-per-kilogram target as well.

Worked examples

How to use it

1. Enter sex, age, height and weight, and pick an equation (Katch-McArdle needs body fat %).
2. Choose your usual activity level; if unsure, choose the lower one.
3. Read the goal table and the macro split.

Frequently asked questions

Related guides

• BMR and TDEE Formulas: A Century of Equations, How Accurate They Are, and Why the 3,500-Calorie Rule Misleads