Calorie Calculator

How your daily calories are calculated

The calculator estimates your resting burn with the Mifflin-St Jeor equation, multiplies it by an activity factor to get your maintenance calories (TDEE), then applies the daily surplus or deficit you choose. It also suggests a macro split from your editable inputs: protein in grams per kilogram, fat as a share of calories, and carbs filling the rest.

Maintenance (TDEE) = BMR × activity factor

Daily target = TDEE + goal adjustment (kcal)

Protein = g/kg × weight · Fat = fat% of kcal ÷ 9 · Carbs = remaining kcal ÷ 4

The resting figure itself — and how Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle differ — is worked through on the BMR calculator. This page is about what you do with it.

Worked example

A 30-year-old woman, 70 kg, 170 cm, moderately active (1.55): BMR ≈ 1,452 kcal, so maintenance ≈ 1,452 × 1.55 = ≈ 2,250 kcal/day. With the 500 kcal deficit the daily target is ≈ 1,750 kcal — roughly 0.45 kg (1 lb) of loss per week. With the default 1.8 g/kg protein and 25% fat, macros come to about 126 g protein, 49 g fat, and 202 g carbs.

What TDEE is made of

Total daily energy expenditure is everything you burn in a day, and it is what decides whether weight moves:

Mifflin-St Jeor is the default because a 2005 systematic review in the Journal of the American Dietetic Association (Frankenfield, Roth-Yousey and Compher) found it the most reliable of the common predictive equations in both non-obese and obese adults. Most reliable is not the same as exact: it still misses measured resting metabolic rate by more than 10% for a sizable minority of people, and every calorie target inherits that band.

Activity factors, and why they carry most of the error

These levels describe your whole week, not your best day:

Moving from moderate to very active raises TDEE by 11.3%, and the full range from sedentary to athlete is a 58% span. Picking the wrong bucket moves the answer further than the BMR equation's error does — and people reliably pick one too high, because a few gym sessions feel like more movement than a job that keeps you standing all day. The 1.9 level is manual work or two sessions a day, not an enthusiastic gym habit.

Steps make a useful cross-check: roughly 0.04 kcal per step per kilogram, so 10,000 steps at 70 kg is about 280 kcal. Watches apply their own version of this, which is why their figures and a formula rarely agree.

Setting a deficit or surplus

The goal menu applies a fixed daily adjustment: −500 kcal to lose weight, +300 for a lean gain, or +500 for a faster one. A kilogram of body fat holds roughly 7,700 kcal (about 3,500 per pound), so 500 a day trends toward 0.45 kg a week. If you prefer a target that scales with body size, the percentage approach gives similar numbers for an average adult:

Deficits much beyond 750 kcal tend to cost muscle and are hard to sustain. On the gaining side, resistance training, protein, sleep, and training history decide how much of the gain is muscle — the surplus only supplies the energy.

Real loss runs slower than the arithmetic. TDEE falls as you get lighter, and prolonged dieting lowers expenditure a further 5–15% below what the equations predict for your new weight — thyroid output falls, NEAT drops quietly, movement becomes more efficient. That is why plateaus arrive without any change in adherence. The practical responses are a week or two at maintenance, or accepting a slower rate; cutting harder deepens the adaptation.

How the macros are split

Protein is set from body weight in grams per kilogram. Fat takes the percentage of calories you choose, and carbohydrate gets whatever energy is left. Protein and carbohydrate supply about 4 kcal per gram, fat about 9. If the protein and fat settings already use up nearly all the calories, carbs approach zero — a sign to revisit the target or the split rather than a meal plan to follow.

Adjusting the estimate against your own data

1. Eat to the target consistently for two to four weeks.
2. Compare weekly average body weight, not single weigh-ins — water and glycogen swing daily readings.
3. If the trend misses the goal, adjust by 100–200 kcal a day; lower the activity factor first.
4. Recalculate after every 4–5 kg of change, or when your activity changes.

Special cases: women, teens, and breastfeeding

• Women use the same equation with a different constant. Energy needs shift across the menstrual cycle by roughly 100–300 kcal, so weekly averages read better than daily ones.
• Teenagers are poorly served by adult equations, because growth itself costs energy. Deliberate deficits during growth should involve a doctor.
• Breastfeeding adds roughly 500 kcal a day for exclusive feeding in the first six months, tapering as solids are introduced. Add it to TDEE before applying any deficit.
• Very muscular or very lean people get a better resting estimate from body fat percentage — see the body fat calculator and the Katch-McArdle option on the BMR page.

These figures are estimates, not medical advice. Food labels, portion estimates, and wearables all add error, so precision to the last calorie is not realistic. Children, pregnant or breastfeeding people, competitive athletes, and anyone with a medical condition or a history of disordered eating should get individual advice from a clinician or registered dietitian. To compare weight with height instead, use the BMI calculator.