Be honest about the activity multiplier
Everything else on this page is arithmetic. The activity level is a judgement call, and it is where most estimates go wrong — because the multiplier ranges from 1.2 to 1.9, picking one level too high inflates your daily target by several hundred calories.
For a 70 kg, 175 cm, 30-year-old man with a BMR of about 1,649, the spread looks like this: sedentary gives 1,979 kcal, moderate gives 2,556, and very active gives 3,133. That is a range of over 1,150 calories from the same body — enough to turn an intended deficit into a surplus.
The common error is rating yourself on your best week rather than your typical one. Three gym sessions among five sedentary desk days is “light,” not “active.” When genuinely unsure, choose the lower option: it is far easier to add calories after two weeks of no progress than to unpick a deficit that was never real.
Reading your result
Enter your age, sex, height, weight, and activity level in metric or imperial units. The calculator estimates your Basal Metabolic Rate and your Total Daily Energy Expenditure — the calories you need to maintain your current weight — plus target intakes for losing or gaining weight at a steady, sustainable pace.
Maintenance, deficit, and surplus
Your TDEE is the balance point: eat that many calories and your weight stays roughly stable. Eating consistently below it creates a deficit and you lose weight; eating above it creates a surplus and you gain. The commonly used figure of a 500-calorie daily deficit corresponds to about half a kilogram of loss per week, which most people can maintain without feeling deprived.
Why it is an estimate, not a rule
No formula can capture your metabolism exactly. The Mifflin-St Jeor equation used here is well regarded for accuracy, but factors like muscle mass, sleep, stress, and how much you fidget all shift the real number. Treat the result as a well-informed starting point: eat at the suggested level for two or three weeks, weigh yourself regularly, and adjust. This tool is for general information and is not medical or dietary advice.