Calorie deficit calculator

What is a calorie deficit calculator?

A calorie deficit calculator is a free online tool that estimates how many calories below your maintenance level you are eating each day, and how quickly that gap translates into weight loss. It compares the energy your body burns in a day (your total daily energy expenditure, or TDEE) with the energy you take in from food and drink. The difference is your daily calorie deficit.

A calorie deficit is the foundation of weight loss: when you consistently consume fewer calories than your body uses, it draws on stored energy (mostly body fat) to make up the shortfall, and you lose weight over time. This calculator turns your age, sex, height, weight, activity level, and daily calorie intake into three practical numbers — your maintenance calories, your daily deficit, and your projected weekly weight loss.

How does the calculator work?

The calculator runs in three stages:

1. Estimate your basal metabolic rate (BMR) — the calories your body needs at complete rest — using the Mifflin-St Jeor equation.
2. Estimate your maintenance calories (TDEE) by multiplying BMR by an activity factor.
3. Compute the deficit by subtracting your reported daily intake from your maintenance calories, then convert that daily deficit into a projected weekly weight loss.

Activity levels

Your activity level scales BMR up to your real-world energy expenditure:

• Sedentary (1.2): little to no exercise.
• Light exercise (1.375): light exercise or sports 1–3 days/week.
• Moderate exercise (1.55): moderate exercise or sports 3–5 days/week.
• Heavy exercise (1.725): hard exercise or sports 6–7 days/week.
• Extra active (1.9): very intense exercise or a physical job.

Formula

The Mifflin-St Jeor equation estimates BMR from weight in kilograms, height in centimetres, and age in years:

For men:

$$\text{BMR} = (10 \times \text{weight}) + (6.25 \times \text{height}) - (5 \times \text{age}) + 5$$

For women:

$$\text{BMR} = (10 \times \text{weight}) + (6.25 \times \text{height}) - (5 \times \text{age}) - 161$$

Maintenance calories (TDEE) and the daily deficit follow:

$$\text{TDEE} = \text{BMR} \times \text{Activity Factor}$$ $$\text{Deficit} = \text{TDEE} - \text{Daily Intake}$$

Because roughly 7700 kcal is stored in 1 kg of body fat (about 3500 kcal per pound), the projected weekly weight loss is:

$$\text{Weekly loss (kg)} = \frac{\text{Deficit} \times 7}{7700} \qquad \text{Weekly loss (lb)} = \frac{\text{Deficit} \times 7}{3500}$$

Examples

Example 1: 30-year-old woman, sedentary, eating 1200 kcal

Individual: 30 years old, 60 kg, 165 cm, sedentary, daily intake 1200 kcal.

• Calculate BMR:

$$\text{BMR} = (10 \times 60) + (6.25 \times 165) - (5 \times 30) - 161 = 1320.25$$

• Calculate TDEE (Sedentary factor = 1.2):

$$\text{TDEE} = 1320.25 \times 1.2 = 1584$$

• Calculate the daily deficit:

$$\text{Deficit} = 1584 - 1200 = 384 \text{ kcal/day}$$

• Projected weekly loss:

$$\frac{384 \times 7}{7700} = 0.35 \text{ kg/week} \qquad \frac{384 \times 7}{3500} = 0.77 \text{ lb/week}$$

Example 2: 30-year-old man, moderate exercise, eating 2000 kcal

Individual: 30 years old, 80 kg, 180 cm, moderate exercise, daily intake 2000 kcal.

• Calculate BMR:

$$\text{BMR} = (10 \times 80) + (6.25 \times 180) - (5 \times 30) + 5 = 1780$$

• Calculate TDEE (Moderate factor = 1.55):

$$\text{TDEE} = 1780 \times 1.55 = 2759$$

• Calculate the daily deficit:

$$\text{Deficit} = 2759 - 2000 = 759 \text{ kcal/day}$$

• Projected weekly loss:

$$\frac{759 \times 7}{7700} = 0.69 \text{ kg/week} \qquad \frac{759 \times 7}{3500} = 1.52 \text{ lb/week}$$

Notes

• A negative deficit means you are eating more than your maintenance calories — a surplus that leads to weight gain rather than loss.
• A moderate, sustainable deficit of about 300–500 kcal per day is widely recommended for steady fat loss without excessive hunger or muscle loss.
• The 7700 kcal-per-kg rule is an approximation. Real weight change also depends on water balance, glycogen stores, and metabolic adaptation, so actual results vary.
• For specific health goals or medical conditions, consult a registered dietitian or healthcare provider before starting an aggressive deficit.

FAQs

What is a calorie deficit?

A calorie deficit is the gap between the calories you burn each day and the calories you eat. When you burn more than you consume, your body uses stored energy to cover the difference, which results in weight loss.

How big should my calorie deficit be?

For most people, a deficit of 300–500 kcal per day is a safe target that yields roughly 0.25–0.5 kg (0.5–1 lb) of weight loss per week. Larger deficits can speed up results but are harder to sustain and may cost muscle.

Why is my projected weight loss only an estimate?

The calculator assumes about 7700 kcal per kilogram of body fat and a constant metabolism. In reality, your TDEE drifts as your weight changes, and short-term scale movements include water and digestive contents, so your real rate of loss will fluctuate.

Can I lose weight without exercising?

Yes. Weight loss is driven by the overall calorie balance, so you can create a deficit through diet alone. Exercise raises your TDEE, which lets you eat a little more while keeping the same deficit, and it supports muscle retention and overall health.

What if the calculator shows a surplus instead of a deficit?

If your daily intake is higher than your maintenance calories, the deficit value becomes negative — a calorie surplus. To lose weight, lower your intake or raise your activity level until the deficit is positive.