What your calories depend on
The calories you need are the ones you burn. The base is your resting energy expenditure: what your body uses to breathe, keep its temperature and run its organs. It depends mostly on your weight, height, age and sex. On top of that comes everything you move during the day, training included.
Eating the same as you burn is called maintenance: your weight stays stable. It is the number you need first, because losing or gaining weight is worked out from it.
How to work out your calories in 3 steps
- Work out your resting expenditure. With the Mifflin-St Jeor equation: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then add 5 if you are a man or take off 161 if you are a woman (Mifflin et al., 1990). It is the equation that most often lands within 10% in healthy adults, with and without obesity (Frankenfield et al., 2005).
- Multiply it by your activity level. Use the factor from the table below. The result is your maintenance.
- Adjust it to your goal. Take calories off to lose fat or add a few to build muscle, depending on the rate you choose.
Example: a 30-year-old woman who is 165 cm and 62 kg has a resting expenditure of 620 + 1,031 − 150 − 161 = about 1,340 calories. If she trains 4 days a week, she multiplies by 1.6 and her maintenance comes to about 2,150 calories. With the same steps, a 30-year-old man who is 178 cm and 78 kg gets about 1,750 calories at rest and 2,800 for maintenance.
The calorie calculator does this math for you and rounds to 50 calories.
Which activity level to choose
| Level | Who it fits | Multiply by |
|---|---|---|
| Light | You train 0 to 2 days a week | 1.50 |
| Moderate | You train 3 to 5 days a week | 1.60 |
| Very active | You train 6 or 7 days a week | 1.75 |
| Athlete | You train twice a day, or have a physical job and also train | 1.90 |
These factors come from the US National Academies' total energy expenditure equations, built on doubly labeled water measurements, the most accurate way to measure what a person burns in everyday life (National Academies, 2023).
Training is already part of the level, so do not add what your watch or the machine says on top. Expenditure also does not grow without limit: in very active people, the body adapts and total expenditure levels off (Pontzer et al., 2016). If you are torn between two levels, pick the lower one.
How many calories to eat for your goal
To lose fat without losing muscle, aim to lose 0.5% to 1% of your body weight per week (Helms et al., 2014). To build muscle without adding extra fat, aim to gain 0.25% to 0.5% (Iraki et al., 2019). Each kilo per week is worth about 1,100 calories a day (7,700 kcal ÷ 7).
| Goal | Rate per week | 62 kg woman | 78 kg man |
|---|---|---|---|
| Lose fat | −0.5% of your weight | 1,800 kcal | 2,350 kcal |
| Maintain | No change | 2,150 kcal | 2,800 kcal |
| Build muscle | +0.25% of your weight | 2,300 kcal | 3,000 kcal |
For the woman in the example, losing 0.5% is 0.31 kg (0.7 lb) a week, about 340 fewer calories a day. For the man, 0.39 kg (0.9 lb), about 430 fewer. If your goal is to lose weight, the calorie deficit guide explains how to choose your rate and keep your muscle.
Once you have your calories, split them into protein, carbs and fat with the macro calculator.
Why it is an estimate and how to adjust it
No equation knows your body. Even Mifflin-St Jeor is off by more than 10% for some people (Frankenfield et al., 2005). For the woman in the example, 10% is about 215 calories either way. That is why the calculator's number is a starting point, not a fixed target.
- Weigh yourself several mornings a week. A single day's weight shifts with water and salt. Look at the weekly average.
- Compare every two weeks. If the average is not moving the way you expected, add or take off 100 to 200 calories and check again.
- Recalculate when your weight changes. A lighter body burns less, so your maintenance changes along with your weight (Hall, 2008).
Questions
How many calories should I eat to lose weight?
Your maintenance minus a deficit that takes off 0.5% to 1% of your body weight per week. In programs for people with overweight, the US guideline usually prescribes 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men, adjusted to each person (Jensen et al., 2014).
Should I add the calories I burn working out?
No, if you already chose your activity level from the days you train: training is included. Adding it again counts it twice, and the expenditure of people who train a lot grows less than it seems (Pontzer et al., 2016).
Is it dangerous to eat under 1,200 calories?
Diets under 800 calories a day are only recommended with medical supervision (Jensen et al., 2014). Mobbe's calculator does not go below 1,200 calories for women or 1,500 for men.
How many calories do I need to build muscle?
A little more than your maintenance: just enough to gain 0.25% to 0.5% of your body weight per week (Iraki et al., 2019). For the man in the example that is about 200 to 430 extra calories a day, along with enough protein and strength training.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. doi:10.1093/ajcn/51.2.241
- Frankenfield D, Roth-Yousey L, Compher C. 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. doi:10.1016/j.jada.2005.02.005
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy. Washington, DC: The National Academies Press; 2023. doi:10.17226/26818
- Pontzer H, Durazo-Arvizu R, Dugas LR, et al. Constrained total energy expenditure and metabolic adaptation to physical activity in adult humans. Curr Biol. 2016;26(3):410-417. doi:10.1016/j.cub.2015.12.046
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20. doi:10.1186/1550-2783-11-20
- Iraki J, Fitschen P, Espinar S, Helms E. Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports (Basel). 2019;7(7):154. doi:10.3390/sports7070154
- Hall KD. What is the required energy deficit per unit weight loss? Int J Obes. 2008;32(3):573-576. doi:10.1038/sj.ijo.0803720
- Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults. Circulation. 2014;129(25 Suppl 2):S102-S138. doi:10.1161/01.cir.0000437739.71477.ee
This guide is for information only and does not replace advice from a health professional.
