Calorie Deficit Calculator

Work out your daily calorie target for weight loss, maintenance, or muscle gain. Personalised to your stats, activity level, and goal — with an estimated timeline to reach your target weight.

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How to Use This Calculator
  1. Enter your details — sex, age, height, and current weight using your preferred unit system.
  2. Enter your target weight — the weight you want to reach.
  3. Choose your activity level — be honest; most people overestimate this.
  4. Select your goal — lose 0.5 kg/wk (moderate), lose 1 kg/wk (aggressive), maintain, or gain.
  5. Click Calculate — see your daily calorie target, macro split, and estimated timeline.
Tip: Your TDEE decreases as you lose weight. Re-calculate every 4–8 weeks to keep your targets accurate.
Frequently Asked Questions

A calorie deficit occurs when you consume fewer calories than your body burns in a day. Your body then uses stored fat (and some muscle) for energy, resulting in weight loss. A deficit of approximately 3,500 kcal equates to roughly 0.45 kg (1 lb) of fat loss, although this varies by individual.

A moderate deficit of 300–500 kcal/day is generally considered safe and sustainable, leading to approximately 0.25–0.5 kg (0.5–1 lb) of weight loss per week. A deficit of 750–1,000 kcal/day is more aggressive (~0.7–1 kg/week) but harder to sustain. Deficits greater than 1,000 kcal/day are not recommended without medical supervision as they can cause muscle loss, nutrient deficiencies, and metabolic adaptation.

A calorie surplus means eating more calories than you burn. This is used when the goal is to gain weight or build muscle. A modest surplus of 200–300 kcal/day is recommended for "lean bulking" to maximise muscle gain while minimising fat gain. Larger surpluses lead to more fat accumulation alongside any muscle gained.

Total Daily Energy Expenditure (TDEE) is calculated using your Basal Metabolic Rate (BMR) — the calories your body needs at rest — multiplied by an activity factor. This calculator uses the Mifflin-St Jeor formula for BMR, which is considered the most accurate for the general population. Your TDEE is your maintenance calorie level — the amount you need to eat to stay at your current weight.

The estimated time depends on your calorie deficit and how much weight you want to lose or gain. Using the rough rule that 1 kg of fat ≈ 7,700 kcal, this calculator estimates your timeline. Bear in mind that weight loss is rarely perfectly linear — it slows over time as your BMR decreases with lower body weight, and can vary week to week due to water retention, hormones, and other factors.
Deficit / Surplus Guide
Daily Deficit Weekly Loss Rate
250 kcal~0.25 kgGentle
500 kcal~0.5 kgModerate
750 kcal~0.75 kgAggressive
1,000 kcal~1.0 kgMax safe

Based on 1 kg ≈ 7,700 kcal. Actual results vary.

Tips for Success
Track your intake

Use a food diary app to log calories accurately. Studies show most people underestimate intake by 20–40%.

Prioritise protein

Eating 1.6–2.0 g protein per kg of body weight while in a deficit helps preserve muscle mass.

Don't go too low

Severe restriction can cause metabolic adaptation, muscle loss, and nutrient deficiencies. Aim for at least 1,200 kcal/day (women) or 1,500 kcal/day (men) unless medically supervised.

Be patient

Sustainable weight loss is 0.5–1 kg per week. Gradual changes are far more likely to be maintained long term.

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