What the calorie calculator measures
This calorie calculator answers one practical question: how many calories should you eat in a day? To get there it works out two numbers that sit at the heart of nutrition — your BMR (basal metabolic rate) and your TDEE (total daily energy expenditure, also called your maintenance calories). BMR is what your body burns at complete rest just to stay alive; TDEE is that figure scaled up for how much you move.
The tool is built for adults. Enter your sex, age, height, weight and activity level, and you get, at a glance:
- your BMR — the energy your body needs at rest,
- your TDEE — your daily calorie need including activity (your maintenance level),
- a daily calorie target for your goal: lose, maintain, or gain weight,
- a protein / carbs / fat split for that target.
You also see how your TDEE compares with other people of a similar profile, so a bare number turns into context. Everything the calculator shows is an estimate to plan from, not a medical prescription — see the accuracy section and FAQ below.
How to use the calorie calculator
- Enter sex, age, height and weight. The BMR equations use all four. Sex here is the biological input the formula needs, not a statement about identity.
- Pick your activity level. Choose the band that matches a typical week, from sedentary to extra active. This sets the multiplier that turns BMR into TDEE.
- Read your BMR and TDEE. They appear instantly. TDEE is your maintenance calories — eat that many and your weight holds steady.
- Set a goal (optional, in advanced options). Choose lose, maintain or gain, and a weekly pace. The calculator applies the matching deficit or surplus and shows your daily target plus a projection over time.
- Fine-tune if you want. Advanced options let you switch the BMR formula, enter body-fat percentage, set your own activity multiplier, and adjust the protein and fat split.
How it works: BMR, TDEE and your calorie target
Basal metabolic rate (BMR)
Your BMR is the energy your body spends at rest — breathing, circulating blood, keeping your organs running. It’s the single biggest slice of what you burn each day. The calculator estimates it from a published regression equation. You can choose between three:
- Mifflin-St Jeor (1990) — the default and the one we recommend for most adults. Men:
10 × weight + 6.25 × height − 5 × age + 5; women:10 × weight + 6.25 × height − 5 × age − 161(weight in kg, height in cm, age in years). A large review by the Academy of Nutrition and Dietetics found it the most reliable predictive equation for resting metabolism in healthy adults. - Harris-Benedict (revised, 1984) — the classic equation, still widely used. It tends to read a little higher than Mifflin-St Jeor.
- Katch-McArdle —
370 + 21.6 × lean body mass. It ignores sex and age and works from your lean mass instead, so it’s the best choice if you know your body-fat percentage. Leave body fat blank and the calculator falls back to Mifflin-St Jeor.
Notice that the male and female Mifflin equations differ only by their constant: +5 versus −161. At the same age, height and weight, the women’s equation returns about 166 kcal less — the main reason a calorie target for a woman is usually lower than for a man of the same size.
From BMR to TDEE: activity multipliers
Almost nobody spends the day at rest, so we multiply BMR by an activity factor (a physical activity level, or PAL) to get TDEE:
TDEE = BMR × activity multiplier
| Activity level | Multiplier |
|---|---|
| Sedentary — little or no exercise | 1.2 |
| Lightly active — 1–3 days/week | 1.375 |
| Moderately active — 3–5 days/week | 1.55 |
| Very active — 6–7 days/week | 1.725 |
| Extra active — hard training or a physical job | 1.9 |
These five multipliers are the standard convention used across fitness and nutrition tools. They aren’t a single published experiment — they’re a practical scale anchored in the physical-activity-level bands the FAO/WHO/UNU expert consultation describes for adults (roughly 1.40 for sedentary living up to around 2.40 for the most demanding lifestyles). If you have a better estimate of your own activity, you can enter a custom multiplier in the advanced options.
Your daily calorie target
Your TDEE is your maintenance target — eat that and weight stays flat. To change weight, you shift calories away from it:
- Maintain: target = TDEE.
- Lose: subtract a deficit. Roughly 7,700 kcal equals one kilogram of body fat, so losing 0.5 kg a week means a deficit of about 550 kcal a day (0.5 × 7,700 ÷ 7). The ACSM considers 0.25–1 kg per week a sensible pace.
- Gain: add a surplus, the same maths in reverse.
The 7,700 kcal-per-kilogram figure is a deliberate linear simplification. In reality, weight loss slows as you go: as you get lighter your body burns a little less, an effect called metabolic adaptation. So treat the projection as an optimistic straight line, not a promise — real progress usually lags it over the months.
Step-by-step example
Take a man, 30 years old, 180 cm, 80 kg, moderately active, using the default Mifflin-St Jeor formula.
- BMR:
10 × 80 + 6.25 × 180 − 5 × 30 + 5= 800 + 1125 − 150 + 5 = 1,780 kcal. - TDEE: 1,780 × 1.55 = 2,759 kcal. That’s his maintenance level.
- To lose about 0.5 kg a week, subtract 550 kcal: his daily target becomes about 2,209 kcal.
Same man, same stats, different formula: Harris-Benedict gives a BMR of about 1,854 and a TDEE of 2,873 kcal — a little higher. Katch-McArdle at 20% body fat (64 kg lean mass) gives a BMR of 1,752 and a TDEE of 2,716 kcal. The spread between methods — here around 150 kcal — is normal and shows why any single number is an estimate.
Macros: protein, carbs and fat
Once your calorie target is set, the calculator splits it into the three macronutrients. By default it allocates 1.6 g of protein per kg of body weight (the mid-range recommended by the International Society of Sports Nutrition) and 27.5% of calories from fat (the middle of the Institute of Medicine’s acceptable range); carbohydrates fill whatever calories remain. The conversion uses the standard Atwater factors — 4 kcal per gram for protein and carbs, 9 kcal per gram for fat. You can change the protein target and fat share in the advanced options.
For the example man above at 2,759 kcal, that works out to about 128 g protein, 84 g fat and 373 g carbs.
Pregnancy and breastfeeding
If you select female, the advanced options let you flag pregnancy or breastfeeding, and the calculator adds the extra energy those states require on top of your TDEE:
- Pregnancy: no meaningful increase in the first trimester, then +340 kcal in the second and +452 kcal in the third (Institute of Medicine, 2009).
- Breastfeeding: about +500 kcal a day in the early months (NICHD).
When either is selected, the calculator forces the target to maintenance and does not apply any deficit — because calorie-restricted diets are not recommended during pregnancy or breastfeeding. These numbers are population estimates to give you a rough idea, nothing more. Energy and weight decisions during pregnancy or lactation should be made with your doctor or a registered dietitian, who can account for your individual situation.
How accurate is this — and what it isn’t
Every number here is an estimate, not medical advice. Prediction equations like Mifflin-St Jeor were built on population averages, so an individual’s true metabolism can sit 5–10% either side of the estimate — even more at very low or very high body weights, where the formulas are less reliable. The gold standard for measuring energy needs is indirect calorimetry, a lab test that measures the gases you breathe; a calculator is a fast, free approximation of it.
Use the result as a sensible starting point, then adjust based on what the scale actually does over two to four weeks. The calculator also flags a common clinical minimum — around 1,200 kcal for women and 1,500 for men (a widely used convention, per MedlinePlus/NIH, not a hard rule) — and warns you if your target drops below it. If you have a medical condition, are pregnant or breastfeeding, or are unsure, talk to a doctor or a registered dietitian before making big changes.