Calorie Deficit Calculator: How Many Calories Should You Eat to Lose Weight?

A calorie deficit is the most fundamental driver of fat loss. When you consistently consume fewer calories than your body burns, it draws on stored body fat for energy. This calculator tells you exactly how large a deficit to create — and how long it will take to reach your goal.

How We Calculate Your Daily Calorie Target

Step 1 — Basal Metabolic Rate (BMR)

We use the Mifflin-St Jeor equation, the most validated formula for general populations:

Gender	Formula
Male	BMR = 10W + 6.25H − 5A + 5
Female	BMR = 10W + 6.25H − 5A − 161

Where W = weight in kg, H = height in cm, A = age in years.

Step 2 — Total Daily Energy Expenditure (TDEE)

BMR is multiplied by an activity multiplier to account for daily movement:

Activity Level	Multiplier	Description
Sedentary	1.20	Desk job, no exercise
Light	1.375	1–2 days/week exercise
Moderate	1.55	3–5 days/week exercise
Active	1.725	6–7 days/week exercise
Very Active	1.90	Physical job or athlete

TDEE is your maintenance calories — the amount needed to stay at your current weight.

Step 3 — Daily Deficit

Your chosen weekly deficit is divided by 7:

Daily Target = TDEE − (Weekly Deficit ÷ 7)

Choosing the Right Deficit Pace

Pace	Daily Deficit	Weekly Loss	Best For
Slow	250 kcal	~0.23 kg (0.5 lb)	Preserving muscle; long-term adherence
Moderate	500 kcal	~0.45 kg (1 lb)	Most people; sustainable
Fast	750 kcal	~0.68 kg (1.5 lb)	Those with significant weight to lose
Aggressive	1000 kcal	~0.91 kg (2 lb)	Short-term; requires medical supervision

The 500 kcal/day deficit is the most commonly recommended, offering a balance between speed and sustainability.

Why 7,700 kcal = 1 kg of Fat?

One kilogram of body fat contains roughly 7,700 kilocalories of stored energy. This is the standard used to estimate fat-loss rates from a calorie deficit. In practice, the actual rate varies slightly because:

• Metabolic adaptation occurs over time (the body becomes more efficient)
• Some weight loss comes from water and glycogen, especially early on
• Muscle tissue has a caloric density much lower than fat

Safety Minimums

Eating too few calories can cause muscle loss, nutrient deficiencies, hormonal disruption, and fatigue. Evidence-based guidelines recommend:

• Women: minimum 1,200 kcal/day
• Men: minimum 1,500 kcal/day

The calculator flags any plan that dips below these thresholds. If this happens, select a smaller deficit or consult a registered dietitian.

Key Principles for Effective Fat Loss

Prioritise Protein

Aim for 1.6–2.2 g of protein per kg of body weight while in a deficit. High protein intake:

• Preserves lean muscle mass
• Increases satiety (protein is the most filling macronutrient)
• Has a higher thermic effect (more calories burned digesting it)

Combine Diet with Resistance Training

Cardiovascular exercise is not required for fat loss — the deficit is what matters. However, strength training helps retain muscle, which keeps your BMR higher and improves body composition even when the scale barely moves.

Progressive TDEE Recalculation

As you lose weight, your BMR decreases. A 10 kg reduction in body weight can lower TDEE by 100–200 kcal/day. Recalculate your targets every 4–6 weeks to avoid a plateau.

BMI vs. Weight Loss Goals

While BMI is a useful population-level screening tool, it doesn't distinguish fat from muscle. A realistic, personalised target weight is more valuable than chasing a BMI number. For a more detailed body composition picture, pair this calculator with the Body Fat Calculator.

Frequently Asked Questions

How accurate is the calorie deficit calculation? The Mifflin-St Jeor equation has a margin of error of ±10% for most people. Use the result as a starting point, track your actual weight change over 2–3 weeks, and adjust by 100–200 kcal if needed.

What if I'm not losing weight at my calorie target? First, verify your food tracking accuracy — studies show people typically under-report intake by 20–40%. If tracking is accurate, reduce the daily target by 100–150 kcal and reassess in 2 weeks.

Can I lose fat without a calorie deficit? No. While hormones, sleep quality, and food composition all influence body composition, a sustained energy deficit is the non-negotiable prerequisite for fat loss.

Should I eat back exercise calories? If your activity multiplier already accounts for your exercise level, you should not eat back calories. If you used "Sedentary" but occasionally exercise, eating back 50–75% of estimated exercise calories provides a reasonable buffer.

How do I maintain weight after reaching my goal? Switch to a maintenance calorie target (your TDEE at your new weight). Gradually increase calories over 2–4 weeks to avoid rapid regain from refeeding.