Calorie Calculator — Step-by-Step Solutions

The Calorie Calculator estimates your daily calorie needs based on your age, gender, height, weight, and activity level using the Mifflin-St Jeor equation. It supports four modes: daily maintenance calories, calories for weight loss, calories for weight gain, and custom deficit or surplus.

Enter your details and get personalised calorie targets instantly. The calculator pairs well with our BMI and TDEE calculators for a complete picture of your nutritional needs.

Age

Gender

Weight (kg)

Height (cm)

Activity Level

Your calculations will appear here

How to Use the Calorie Calculator

Choose a mode: Daily Needs for maintenance calories, Lose Weight for deficit options, Gain Weight for surplus options, or Custom Deficit/Surplus for your own number.
Enter your age and sex, choose Metric or Imperial, and enter your weight and height. Then pick your activity level, from sedentary to very active.
In Custom mode type the daily calorie adjustment: a negative number such as -500 for a deficit or a positive one for a surplus. The estimated weekly weight change appears below the target.
Results are estimates and not medical advice. Check with a doctor or dietitian before making big changes to how you eat.

Formula and Theory

Your daily calorie need is your maintenance level (TDEE) plus or minus an adjustment. TDEE is your BMR from the Mifflin-St Jeor equation multiplied by an activity factor between 1.2 and 1.9. Eating at that level roughly maintains your weight; the Lose and Gain modes subtract or add fixed amounts.

The weekly weight change is estimated using the common rule of thumb that about 7,700 kilocalories correspond to 1 kilogram of body fat. A daily deficit of 500 kcal adds up to 3,500 per week, or roughly 0.45 kg. The rule is only an approximation, since real changes also involve water, muscle and metabolic adaptation, so weight does not change in a straight line.

The loss options shown are mild (250 kcal below maintenance), moderate (500) and extreme (1,000). The labels in the tool are rounded. Large deficits can be hard to sustain and may not suit everyone, so seek professional advice for personal targets.

Everything here is a population-based estimate. It is not medical advice, and it does not suit children, pregnancy, breastfeeding or people with medical conditions.

Worked Examples

Example 1: Maintenance calories

Problem: A 35-year-old woman, 65 kg, 165 cm, lightly active (factor 1.375). How many calories to maintain weight?

Solution: BMR = 10 x 65 + 6.25 x 165 - 5 x 35 - 161 = 1,345.25. TDEE = 1,345.25 x 1.375 = 1,849.7.

Answer: About 1,850 kcal/day

Example 2: Weight loss options

Problem: For the same woman, what are the mild, moderate and extreme loss targets?

Solution: Mild: 1,849.7 - 250 = 1,599.7. Moderate: 1,849.7 - 500 = 1,349.7. Extreme: 1,849.7 - 1,000 = 849.7. The tool rounds these to whole numbers. The extreme target is very low for most people, so it deserves a conversation with a professional before use.

Answer: 1,600, 1,350 and 850 kcal/day

Example 3: Estimating weekly change for a custom deficit

Problem: A deficit of 500 kcal a day: what weekly change does the calculator estimate?

Solution: Weekly deficit = 500 x 7 = 3,500 kcal. Divide by 7,700 kcal per kg: 3,500 / 7,700 = 0.4545 kg.

Answer: About -0.45 kg per week

Example 4: Weight gain options

Problem: For the same woman, what are the mild and moderate gain targets, and what does the moderate one mean per week?

Solution: Mild: 1,849.7 + 250 = 2,099.7. Moderate: 1,849.7 + 500 = 2,349.7. A 500 kcal surplus is 3,500 kcal a week, and 3,500 / 7,700 = 0.45 kg.

Answer: 2,100 and 2,350 kcal/day; about +0.45 kg per week at the moderate level

Frequently Asked Questions

How many calories should I eat a day?

It depends on your age, sex, size and activity. The Daily Needs mode estimates your maintenance level; whether to eat more or less than that is a personal decision best made with a doctor or dietitian.

How many calories make a kilogram of fat?

The usual rule of thumb is about 7,700 kcal per kilogram, or 3,500 per pound. It is an approximation, and real weight change varies from person to person.

Is a 1,000 calorie deficit safe?

It is a large deficit, and it can leave very low intake for smaller or lighter people. Such a plan should be discussed with a doctor or registered dietitian first. This tool only reports the arithmetic.

Why does my weight not change at the predicted rate?

Water, salt, hormones and changes in activity move the scale day to day, and your body adapts to long deficits. Look at the trend over several weeks rather than daily numbers.

Which formula does the calculator use?

Mifflin-St Jeor for BMR, then the standard activity multipliers. This is the formula most dietitians prefer for healthy adults, though it is still an estimate.

Do I need to eat back exercise calories?

No. The activity level you choose already includes your usual exercise. Count it only if you do much more or less than usual.