How is the calorie deficit worked out?

We estimate your basal metabolic rate with the Mifflin-St Jeor equation, multiply by an activity factor to get your total daily energy expenditure (TDEE), then subtract a deficit based on your weekly goal. About 7,700 kcal equals one kilogram of body fat.

How big a deficit is safe?

Most guidance suggests losing 0.25–1 kg per week. The calculator warns if your target falls below a commonly cited minimum of 1,200 kcal (women) or 1,500 kcal (men) — consider a slower pace or professional advice if so.

Is my data sent anywhere?

No. Every calculation runs entirely in your browser and nothing is uploaded or stored.

How many calories is 1 kg of fat?

Roughly 7,700 kcal. To lose 0.5 kg per week you need a 3,850 kcal weekly deficit, which is about 550 kcal per day. Losing 1 kg per week requires a 7,700 weekly deficit, or about 1,100 kcal per day — aggressive for most people.

Why did the calculator warn my target is too low?

It applies a safety floor of 1,500 kcal/day for men and 1,200 for women. If a fast weekly goal pushes your target below that, it flags it so you choose a slower pace. Eating too little risks muscle loss and nutrient gaps.

Will I keep losing exactly 0.5 kg a week forever?

No. As you get lighter your TDEE falls, so the same intake becomes a smaller deficit and loss slows. Recalculate every few kilograms and adjust your target to keep progress steady.

Do I need to exercise to be in a deficit?

No — a deficit is created by intake below TDEE, achievable through diet alone. Exercise raises your TDEE (and the activity factor here), letting you eat more at the same deficit, and helps preserve muscle while losing fat.

Calorie Deficit Calculator

Calorie deficit calculator

A calorie deficit means eating fewer calories than your body burns — it is the one mechanism behind every form of fat loss. This calculator works out your maintenance calories (TDEE) and then a safe daily intake to hit your chosen rate of loss, so you can stop guessing and eat to a number. It is built for anyone starting a diet who wants a realistic, sustainable target rather than a crash plan.

How it works

The tool computes your BMR with the Mifflin-St Jeor equation (10 × kg + 6.25 × cm − 5 × age, +5 men / −161 women), multiplies by your activity factor to get TDEE, then subtracts a daily deficit. The deficit comes from your weekly goal using the rule that 1 kg of body fat ≈ 7,700 kcal:

daily deficit = (kg per week × 7,700) ÷ 7

A safety floor (1,500 kcal men, 1,200 women) flags targets that are too aggressive.

Example

A 30-year-old man, 178 cm, 80 kg, lightly active, aiming to lose 0.5 kg/week:

BMR = 10×80 + 6.25×178 − 5×30 + 5 = 1,768 kcal
TDEE = 1,768 × 1.375 = 2,431 kcal (maintenance)
Deficit = (0.5 × 7,700) ÷ 7 = 550 kcal/day
Target = 2,431 − 550 = 1,881 kcal/day

Weekly goal	Daily deficit	Approx. result
Lose 0.25 kg	275 kcal	gentle, easy to sustain
Lose 0.5 kg	550 kcal	recommended for most
Lose 1 kg	1,100 kcal	aggressive, often hits the floor

Everything runs in your browser — nothing is uploaded.