What is a calorie calculator?
A calorie calculator estimates how much energy, in kilocalories (kcal), your body uses in a typical day, which is the amount you'd eat to keep your weight steady. This one also gives a lower figure for gradual weight loss and a higher one for weight gain, using your sex, age, height, weight and activity level.
The maintenance figure is often called your TDEE, short for total daily energy expenditure.
How the calculation works
There are two steps.
1. Estimate your basal metabolic rate (BMR) with the Mifflin-St Jeor equation (Mifflin et al., 1990):
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
2. Multiply by an activity factor to get maintenance calories:
| Activity level in the calculator | Description | Multiplier |
|---|---|---|
| Sedentary | Little or no exercise | 1.2 |
| Light | Exercise 1 to 3 days a week | 1.375 |
| Moderate | Exercise 3 to 5 days a week | 1.55 |
| Active | Exercise 6 to 7 days a week | 1.725 |
| Very Active | Physical job or hard training | 1.9 |
These five factors are the scale most commonly published alongside the Harris-Benedict and Mifflin-St Jeor equations. They're broad categories, so treat them as a rough adjustment.
The weight-loss figure is maintenance minus 500 kcal and the weight-gain figure is maintenance plus 500 kcal. All three results are rounded to the nearest whole calorie.
Worked example
A 35-year-old man, 180 cm tall, weighing 80 kg, who exercises 3 to 5 days a week (Moderate):
- BMR: 10 × 80 + 6.25 × 180 − 5 × 35 + 5 = 800 + 1,125 − 175 + 5 = 1,755 kcal
- Maintenance: 1,755 × 1.55 = 2,720.25, shown as 2,720 kcal/day
- Weight loss: 2,720.25 − 500 = 2,220 kcal/day
- Weight gain: 2,720.25 + 500 = 3,220 kcal/day
For a 30-year-old woman, 165 cm and 65 kg, with Light activity, the BMR is 1,370.25 and maintenance is 1,370.25 × 1.375 = 1,884 kcal/day, with 1,384 for loss and 2,384 for gain.
About the 500-calorie rule
Cutting 500 kcal a day is the classic advice for losing about 0.5 kg (1 lb) a week. It comes from the estimate that a pound of body fat stores roughly 3,500 kcal, so 500 × 7 days = 3,500.
The rule works as a starting point, but it overstates long-term loss. As you lose weight, your BMR and the energy cost of moving both fall, so the same intake produces a smaller deficit over time. The U.S. National Institutes of Health's Body Weight Planner, built on research models of how bodies adapt, accounts for this and is a good next step if you want a projection over months.
How to use the result
- Start with the maintenance figure and track what you actually eat for two or three weeks.
- Weigh yourself under the same conditions a few times a week and look at the trend, not single days.
- If your weight is stable, your real maintenance is close to what you're eating. If it's moving, adjust by 100 to 200 kcal and check again.
The formula gives you a sensible first guess. Your own trend over a few weeks is the better measure.
Limits
- The equation is based on population averages and doesn't know your body composition. Muscular people often burn more than predicted.
- It's meant for adults. Children, teenagers, and anyone pregnant or breastfeeding have different energy needs.
- The calculator doesn't apply a minimum intake beyond zero. If the weight-loss figure looks very low for you, get professional advice rather than following the number.
Related calculators
- BMR calculator: just the resting calorie burn, step 1 above.
- BMI calculator: check whether your current weight is in the healthy range.
- Ideal weight calculator: a reference weight for your height to aim for.
- Body fat calculator: track fat loss, not just scale weight.
This calculator is for general information and doesn't replace advice from a doctor or registered dietitian.
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