Woman, 30, 165 cm, 62 kg, lightly active
Her basal rate is about 1 340 kcal, and light activity brings the daily total to roughly 1 843 kcal.
That is the maintenance figure: eat around it and the scale should hold steady.
Calorie calculator
How much energy your body uses in a day, and what to eat to hold, lose or gain weight. Three published equations, a macro split, and the honest error bars.
These figures are estimates for healthy adults and are not medical advice. Speak to a doctor or dietitian before starting a restrictive diet, and always if you have a medical condition.
Result
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How it works
Your body spends energy in two ways. The basal metabolic rate is what it burns doing nothing at all — breathing, pumping blood, keeping warm. For most adults that is between 60 and 70 percent of the daily total. Everything else, from walking to the kitchen to a marathon, sits on top.
The equations estimate the basal rate from height, weight, age and sex, then multiply by an activity factor. Mifflin-St Jeor is the default because it has held up best against measurement in the general population. Harris-Benedict, the older standard, tends to read slightly high. Katch-McArdle ignores sex entirely and works from lean mass, which makes it the sharpest of the three if you actually know your body fat, and the worst if you are guessing.
The activity factor is the weakest link. Most people place themselves one step too high, which is the single most common reason a calorie target quietly fails. If you are unsure between two levels, pick the lower one and adjust after a few weeks of real data.
Formulas used
Mifflin-St Jeor basal metabolic rate
BMR = 10 × kg + 6.25 × cm − 5 × age + s
- kg
- weight in kilograms
- cm
- height in centimetres
- s
- +5 for men, −161 for women
Daily energy expenditure
TDEE = BMR × activity factor
Factors run from 1.2 (sedentary) to 1.9 (extremely active).
Weight change from a calorie gap
kg per week = daily gap × 7 ÷ 7 700
A kilogram of body mass stores roughly 7 700 kcal.
Worked examples
The same, aiming to lose steadily
A 500 kcal daily deficit puts the target near 1 343 kcal and predicts about 0.45 kg lost a week.
It clears the 1 200 kcal floor, but not by much — which is why a slower pace usually suits a smaller person better.
Man, 40, 180 cm, 90 kg, moderately active
Basal rate 1 830 kcal, maintenance about 2 837 kcal with training three to five days a week.
The same 500 kcal deficit leaves 2 337 kcal a day — comfortably above his basal rate, and sustainable for months.
Assumptions and limits
- The equations apply to healthy adults, not to children, pregnancy or illness.
- The activity factor covers your whole week, not just training days.
- Roughly 7 700 kcal are assumed per kilogram of body mass gained or lost.
- Medication, thyroid conditions and metabolic adaptation are not accounted for.
Frequently asked questions
Which equation should I choose?
Mifflin-St Jeor unless you have a reason not to. It was built on a more representative sample than Harris-Benedict and is the one most dietitians reach for.
Katch-McArdle beats both if you have a reliable body fat measurement — a DEXA scan, not a bathroom scale reading. With a guessed figure it is the least accurate of the three.
Why does another calculator give me a different number?
Different equation, different activity factors, or both. The spread between published methods is easily 200 kcal for the same person.
None of them is the truth. The number that matters is the one your own weight trend confirms after three or four weeks.
Is a 1 000 kcal deficit safe?
It is aggressive. For a large, active person it can be reasonable for a limited period; for a smaller one it often lands below the basal rate, which is neither pleasant nor sustainable.
The calculator warns you when the target drops below your basal rate or below the usual adult floor. Losing more slowly preserves more muscle and is far easier to keep to.
Do I have to track macronutrients?
No. Total calories drive weight change; macros mostly affect how you feel and what you keep. The table is there if you want a starting split.
If you only change one thing, make it protein: it is the most filling of the three and the most protective of muscle in a deficit.
Sources
- Mifflin MD, St Jeor ST et al., A new predictive equation for resting energy expenditure, 1990
- Roza AM, Shizgal HM, The Harris-Benedict equation reevaluated, 1984
- Katch F, McArdle W, Nutrition, Weight Control and Exercise
Updated