Article — Calorie Calculator
Calorie calculator
Daily calorie needs for most adults fall between 1,600 and 3,000 kcal. The exact number depends on age, sex, weight, height, and activity. The calorie calculator on this page uses the Mifflin-St Jeor BMR equation (1990) and standard activity multipliers from 1.2 to 1.9 to produce a personal estimate of total daily energy expenditure (TDEE).
USDA dietary guidelines list 2,000 kcal as the default value on food labels, but that figure is a population reference, not a personal target. A 60-year-old woman who walks the dog and a 22-year-old male soccer player can sit 1,200 kcal apart on the same day.
What the calorie calculator shows
The calculator produces four numbers. BMR is what your body burns at rest in 24 hours — heart, brain, kidneys, the basic cost of staying alive. TDEE multiplies BMR by an activity factor for everything you do on top: exercise, walking, fidgeting, work. The daily target adjusts TDEE up or down depending on whether you want to lose, maintain, or gain weight, and at what weekly rate. The fourth number is the implied weekly change in kilograms.
For most users the daily target is the figure that matters. If you eat that amount day-to-day, your body weight should track the goal you picked. The other three numbers explain how the target was derived.
The Mifflin-St Jeor calorie formula
Mifflin and colleagues published a revised BMR equation in the American Journal of Clinical Nutrition in 1990. The Academy of Nutrition and Dietetics and the National Institutes of Health adopted it as the preferred BMR formula for healthy non-obese adults because it tracks measured BMR more closely than the older Harris-Benedict equation.
BMR (male) = 10W + 6.25H − 5A + 5BMR (female) = 10W + 6.25H − 5A − 161TDEE = BMR × activity1 kg fat ≈ 7,700 kcalWeight is in kilograms, height in centimeters, age in years. Imperial inputs (lb, in) are converted before the formula is applied — pounds divided by 2.20462, inches multiplied by 2.54.
Calorie needs by activity level
Activity multipliers were derived from doubly-labeled-water studies and have been standard for two decades. They cover both formal exercise and the smaller but constant cost of non-exercise activity thermogenesis (NEAT) — fidgeting, standing, walking to the printer.
- Sedentary = 1.2 (desk job, no formal exercise)
- Lightly active = 1.375 (1-3 short sessions / week)
- Moderately active = 1.55 (3-5 sessions / week)
- Active = 1.725 (6-7 sessions / week)
- Very active = 1.9 (hard daily training or physical labor)
Most office workers who exercise three times a week land in moderately active, not active. Honest self-classification matters more than the formula precision: dropping one tier on the activity scale subtracts 300 to 400 kcal from the daily target.
Calorie targets for weight loss
One kilogram of body fat stores roughly 7,700 kcal. Aim to lose half a kilogram per week and you need a daily deficit of about 550 kcal. Aim for a kilogram a week and the deficit doubles to roughly 1,100 kcal per day. The calculator handles this arithmetic when you pick the weekly rate.
The 7,700 kcal/kg figure traces back to Max Wishnofsky in 1958. It is a rule of thumb, not a law — early weight loss is largely water and glycogen, and the body's resting metabolism falls slightly as fat mass falls. Real loss usually plateaus at about 80 percent of the model's prediction over a year.
NIH guidelines suggest most healthy adults should not eat below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Below that, micronutrient gaps become hard to avoid and lean-mass loss accelerates.
Calorie calculator worked example
Take a 30-year-old male, 77 kg, 175 cm, moderately active, wanting to lose 0.5 kg per week. BMR is 10 × 77 + 6.25 × 175 − 5 × 30 + 5 = 1,719 kcal. TDEE is 1,712 × 1.55 = 2,664 kcal. The deficit is 0.5 × 7,700 ÷ 7 = 550 kcal/day. The daily target is 2,664 − 550 = 2,114 kcal.
A 30-year-old female, 65 kg, 165 cm, lightly active, maintenance goal. BMR is 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 1,370 kcal. TDEE is 1,370 × 1.375 = 1,884 kcal. The daily target is 1,884 kcal because the goal is maintenance.
Common calorie-counting mistakes
Self-reported food intake is usually under-counted by 20 to 40 percent in adults. Weighing food is more accurate than eyeballing portions. Liquid calories — drinks, oils, dressings — are the most common source of hidden intake, and a single restaurant meal averages 1,200 kcal in the United States according to USDA tracking surveys.
- Eyeball portions = 20-40% under-count vs scale
- Drinks and oils = +200-500 hidden kcal / day
- Restaurant meals = 1,200 kcal average
- Tasting while cooking = +100-200 kcal / day
- Weekend drift = +500 kcal vs weekdays
Calories vs kilojoules
The food calorie on a label is technically a kilocalorie (kcal) — the energy to raise the temperature of one kilogram of water by one degree Celsius. The SI unit is the joule, and one kcal equals 4.184 kJ. Australia, New Zealand, and some European labels use kJ; the US, UK, and much of Asia label in kcal. A 2,000 kcal day is 8,368 kJ.
Wilbur Atwater, the American chemist who built the first human respiration calorimeter in the 1890s, settled the 4 / 4 / 9 kcal-per-gram figures for carbohydrate, protein, and fat that food labels still use today. Atwater chose the kilocalorie over the joule precisely because he wanted a unit ordinary people could relate to — he was writing for USDA leaflets, not for physicists.
Compare your maintenance TDEE to what you actually eat for a week before changing anything. Most people are surprised by the answer — either by how much they eat or by how little — and that surprise is the most useful output of any calorie calculator.
Daily calorie quick reference
- 1 g carbohydrate = 4 kcal
- 1 g protein = 4 kcal
- 1 g fat = 9 kcal
- 1 g alcohol = 7 kcal
- 1 kcal = 4.184 kJ
- USDA label default = 2,000 kcal/day
- Sustainable loss = 0.5-1.0 kg / week
If the calculator says 2,100 kcal and the scale will not move after three weeks, drop by 150 kcal and try again. If you lose faster than the target rate, add 150 kcal back. The formula is a starting point, not a prescription — your body's actual energy use can sit five to ten percent above or below the model.