What is a calorie deficit?

A calorie deficit means consuming fewer calories than your body burns each day. The difference is supplied from energy stores — primarily fat — which is why a sustained deficit produces weight loss. Roughly 7,700 calories are stored per kilogram of body fat, so a deficit of about 1,100 cal/day produces 1 kg of fat loss per week.

What is a safe rate of weight loss?

Most clinicians recommend 0.5–1 kg (about 1–2 lb) per week. Faster rates are possible short-term but risk muscle loss, nutrient deficiencies and rebound weight gain. The calculator caps the daily deficit at sensible limits and warns when goals are too aggressive.

How are BMR and TDEE calculated?

BMR (basal metabolic rate) is calculated with the Mifflin–St Jeor equation, which is the most accurate predictive formula for the general adult population. TDEE (total daily energy expenditure) is BMR multiplied by an activity factor (1.2 sedentary to 1.9 very active).

Why does my deficit shrink as I lose weight?

As you lose weight, your BMR falls because there is less mass to maintain. Recalculate every 2–3 kg of progress to keep your daily target accurate.

Can I lose weight without exercising?

Yes — weight loss is driven primarily by the calorie deficit. Exercise increases TDEE so you can either lose faster at the same intake or eat more at the same rate of loss. It also helps preserve muscle mass during weight loss.

🔥 Calorie Deficit Calculator

Find your daily calorie target to lose weight at a safe, sustainable rate. BMR, TDEE and weeks-to-goal in one place.

Units

Sex

Age (years)

Activity level

Current weight (kg)

Goal weight (kg)

Height (cm)

Target rate of loss

⚠️ Not medical advice. Calorie targets are estimates. Consult a GP, registered dietitian or qualified coach before starting a calorie-deficit programme — especially if you are pregnant, breastfeeding, under 18, or managing a medical condition.

About the Calorie Deficit Calculator

The Calorie Deficit Calculator turns your stats and goals into a concrete daily calorie number — and tells you how long the journey will take. It uses the well-validated Mifflin–St Jeor equation for basal metabolic rate (BMR) and standard activity multipliers for total daily energy expenditure (TDEE).

The science in brief

BMR — the calories you burn at complete rest, just keeping the body running.
Mifflin–St Jeor (men): BMR = 10·W + 6.25·H − 5·A + 5
Mifflin–St Jeor (women): BMR = 10·W + 6.25·H − 5·A − 161
(W in kg, H in cm, A in years)
TDEE = BMR × activity factor (1.2 sedentary → 1.9 very active). This is your maintenance calorie level.
Calorie deficit = TDEE − goal calories. Body fat stores ~7,700 cal per kg, so a daily deficit of 550 cal yields ~0.5 kg loss per week.

How fast should I lose weight?

Most clinicians recommend 0.5–1 kg per week (about 1–2 lb). Faster rates are achievable short-term but increase the risk of:

Lean-muscle loss (which lowers your BMR further)
Hunger-driven binge cycles and rebound weight gain
Nutrient deficiencies, fatigue and reduced training performance

The calculator displays a difficulty assessment and warns if your daily target falls below safe minimums (1,500 cal for men, 1,200 cal for women).

How macros are estimated

The default split is 40% carbs, 30% protein, 30% fat, with protein floored at 1.6 g/kg of body weight to support muscle retention during the deficit. Macro grams are derived from the daily calorie target (carbs and protein = 4 cal/g, fat = 9 cal/g).

Common uses

Setting a starting calorie target for a weight-loss programme
Estimating how long a goal will take so you can plan around events
Pairing with our BMI, Ideal Weight and Calorie/TDEE calculators
Recalculating every 2–3 kg as your BMR drops with weight loss

Frequently Asked Questions

Why is my goal calorie target so low? The calculator caps the daily deficit so you never drop below the medically accepted minimums. If your target hits the floor, choose a slower rate of loss or increase your activity level.

Should I count calories from drinks? Yes. Liquid calories from soft drinks, juices, alcohol and sweetened coffee count toward the same target.

What about cheat days? A weekly average matters more than perfect daily adherence. A modestly higher day at the weekend balanced by lower weekdays still produces the projected weekly deficit.

Why does my BMR drop as I lose weight? Less body mass needs less energy to maintain. Recalculate every 2–3 kg of progress to keep your target accurate.

Is this safe for everyone? No. Calorie restriction is not appropriate for under-18s, pregnant or breastfeeding people, those with eating disorders, or those managing certain medical conditions. Always consult a qualified clinician first.

⚠️

Important Note: This tool provides estimates and is not a substitute for medical advice. Always consult a qualified healthcare provider, registered dietitian or licensed coach before starting any calorie-restricted diet — especially if you have a medical condition.

Related Calculators

TDEE Calculator — Total Daily Energy Expenditure with BMR + cut/maintain/bulk targets.
Macro Calculator — Daily protein, carbs and fat split with cut/maintain/bulk presets and four split styles.
Daily Calorie Calculator — TDEE based on age, weight, height and activity level.