How this calorie calculator works
FitNumbra uses a transparent, widely used method:
Example: a 30-year-old man, 180 cm, 80 kg, moderately active: BMR = 1,780 kcal; maintenance = 1,780 × 1.55 ≈ 2,759 kcal; to lose weight: 2,759 − 500 ≈ 2,259 kcal/day.
Choosing your activity level
| Activity level | Multiplier | Typical routine |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise 1–3 days a week |
| Moderately active | 1.55 | Moderate exercise 3–5 days a week |
| Very active | 1.725 | Hard exercise 6–7 days a week |
| Extra active | 1.9 | Physical job plus training, or training twice a day |
Calorie targets for weight loss and gain
A daily deficit of about 500 kcal is a common starting point for gradual weight loss. Because roughly 7,700 kcal is often used as an approximation for 1 kg of body fat, that works out to around 0.5 kg (1 lb) per week in theory — but real results vary, and weight loss usually slows over time as your body adapts.
For weight gain, a surplus of 250–500 kcal per day combined with strength training helps more of the gain come from muscle.
How to fine-tune your number
- Eat at your target consistently for 2–3 weeks.
- Weigh yourself a few times a week at the same time of day and look at the average.
- If your weight is not changing as expected, adjust by 100–200 kcal a day and review again.
- Pair your calorie target with enough protein — see the protein calculator — and a sensible macro split.
When to get professional advice
Calorie estimates are not suitable for people who are pregnant or breastfeeding, under 18, have a history of eating disorders, or are managing conditions such as diabetes or kidney disease. In these situations, please speak to a doctor or registered dietitian.
Frequently asked questions
How many calories should I eat a day?
It depends on your size, age, sex and activity. The calculator estimates maintenance calories from your BMR and activity level; many adults fall somewhere between about 1,600 and 3,000 kcal per day.
Which formula does this calculator use?
It uses the Mifflin–St Jeor equation for BMR, which reviews have found to be one of the more accurate predictive equations for healthy adults, multiplied by a standard activity factor.
How accurate is a calorie calculator?
Predictive equations are usually within about 10% for most people but can be further off for individuals. Treat the result as a starting estimate and adjust based on your real progress.
Is a 500-calorie deficit safe?
For many healthy adults it is a moderate deficit, but it is not appropriate for everyone. If your target is very low or you have a health condition, speak to a healthcare professional first.
Methods and sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
- Frankenfield D, et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775–789.
- Dietary Guidelines for Americans, 2020–2025 (estimated calorie needs) (opens in a new tab)
Content reviewed: by the FitNumbra editorial team.