Calorie Calculator

Calorie Calculator

This finds your maintenance calories — the intake at which your weight holds steady — and then the targets for losing or gaining at a sustainable rate. The arithmetic rests on a well-worn approximation: roughly 7,700 calories correspond to a kilogram of body mass, so a deficit of about 500 calories a day produces something near half a kilogram a week. That approximation is useful for setting a starting point and unreliable as a long-run prediction, because the body adapts. Maintenance calories fall as you lose weight, both because a smaller body costs less to run and because unconscious activity tends to decline during a deficit. Expect to recalculate every few kilograms rather than to follow one number to a goal.

How this is calculated

BMR comes from the Mifflin-St Jeor equation, then is multiplied by your activity factor to give total daily energy expenditure — your maintenance level. Loss and gain targets adjust that figure by roughly 500 calories a day for a half-kilogram weekly change, and about 1,000 for a kilogram.

Worked example for a 30-year-old woman at 65 kg, 165 cm, lightly active: BMR is about 1,364 calories. At an activity factor of 1.375, maintenance is roughly 1,875. A moderate loss target would be around 1,375 a day.

The 7,700-calories-per-kilogram figure is an approximation derived from the energy density of adipose tissue. It holds reasonably in the short term and drifts over longer periods as body composition and metabolic rate change.

Why weight loss stalls even when you keep eating the same

A lighter body burns fewer calories doing everything, so the deficit you started with shrinks as you succeed. Someone who began at a 500-calorie deficit may be at 300 after losing ten kilograms, without changing a thing.

Adaptive thermogenesis compounds this. During sustained restriction, unconscious activity falls — less fidgeting, less spontaneous movement — and this can account for several hundred calories a day. It is not a metabolic defect; it is the body doing exactly what it evolved to do.

The fix is to recalculate maintenance every few kilograms and to build in maintenance breaks rather than extending a deficit indefinitely.

Setting a rate you can actually sustain

Half a kilogram a week is the usual recommendation for most people, and around 1% of body weight per week is a reasonable ceiling. Faster loss increases the share coming from muscle rather than fat, and is much harder to adhere to.

Protein intake matters more than the exact deficit for preserving muscle — commonly cited targets are in the range of 1.6 to 2.2 grams per kilogram of body weight during a deficit. Resistance training alongside the deficit does more to protect lean mass than any adjustment to the calorie number.

For weight gain the same logic runs in reverse: a surplus of 250 to 500 calories a day supports muscle growth without excessive fat gain, and larger surpluses mostly add fat.

How to use the calorie calculator

Enter your details and activity level. Be honest about activity. Overestimating it is the most common reason a calculated target does not work.
Start at the maintenance figure. Eat at it for two weeks and track your weight. If it holds steady, the estimate is right for you.
Apply a deficit or surplus from there. Use the loss or gain rows. Recalculate every few kilograms, because maintenance moves as your weight does.

Frequently asked questions

How many calories should I cut to lose weight?

A 500 cal/day deficit loses roughly 0.5 kg (1 lb) per week — a sustainable pace. Avoid eating below your BMR for extended periods without medical supervision.

Why am I not losing weight at my calculated calories?

Formulas estimate averages; individuals vary ±10–15%, and intake is easy to under-count. Track honestly for two weeks and adjust by 100–200 calories based on actual results.

Why did my weight loss stall?

Because maintenance calories fall as you get lighter — the deficit you started with shrinks as you succeed. Sustained restriction also reduces unconscious daily movement, which can account for several hundred calories. Recalculate your maintenance every few kilograms rather than following one number to the goal.

How fast should I lose weight?

Around 0.5 kg a week suits most people, with about 1% of body weight per week as a sensible ceiling. Faster loss takes a larger share from muscle and is much harder to sustain. Adequate protein and resistance training protect lean mass more effectively than adjusting the calorie figure does.

Is 1,200 calories a safe target?

It is often too low for an adult and is frequently the output of an unrealistically sedentary activity setting rather than a considered plan. Very low intakes make adequate protein and micronutrients hard to achieve and tend to produce rebound. If your calculated target lands near that figure, check the activity level you selected first.