Calories
A calorie (kcal) is a unit of energy. Your weight changes when the energy you eat is consistently more or less than the energy you use.
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Why calories matter
Your body weight follows energy balance: eat more than you use and you store the extra; eat less and you draw on your stores. Macros matter for what you gain or lose (muscle or fat), but calories decide the direction.
| Nutrient | Energy per gram |
|---|---|
| Protein | 4 kcal |
| Carbohydrate | 4 kcal |
| Fat | 9 kcal |
| Alcohol | 7 kcal |
As a guide, the NHS uses 2,000 kcal a day for women and 2,500 kcal for men, but your own needs depend on your size, age and activity1.
Work out your maintenance calories
Maintenance is the number of calories that keeps your weight steady. It's made up of your basal metabolic rate (BMR, the energy your body uses at rest, usually 60–70% of the total), the energy used digesting food (about 10%) and everything you do on the move, from training to walking and fidgeting.
The calculator uses the Mifflin-St Jeor equation2, which predicted resting energy use within 10% of measured values for more people than other common equations3. It's then multiplied by an activity factor.
Deficits and surpluses
| Goal | Calories | Rate to aim for |
|---|---|---|
| Lose fat | 10–25% below maintenance | 0.5–1% of body weight a week4 |
| Maintain | Around maintenance | Stable weekly average |
| Build muscle | 5–15% above maintenance | 0.25–0.5% of body weight a week5 |
The old rule that 3,500 kcal (7,700 kcal per kg) equals a pound of fat is fine for the first few weeks, but it overestimates weight loss over months, because your energy use falls as you get lighter6. That's why progress slows and why you'll need to recalculate as you go.
Research spotlight
A lasting change in daily calories doesn't move your weight in a straight line: about half of the eventual change happens in the first year and nearly all of it within about three years, because the energy you use adjusts as your weight changes.
Common myths
MythAll calories are the same.
FactFor weight, energy balance rules. But 500 kcal of chicken and vegetables keeps you fuller, and supports muscle better, than 500 kcal of sweets.
MythStarvation mode stops weight loss.
FactYour body does adapt to dieting by burning a bit less, but it doesn't stop fat loss while you're in a real deficit. Stalls are usually water, or a deficit that's smaller than you think.
MythEating late makes you gain weight.
FactWhat you eat across the day matters much more than the time. See The best time to eat.
Track this in NutriLog
Get your personal calorie target
Answer a few questions and NutriLog works out your maintenance and daily targets, then tracks your weight to show whether they're right.
Free to use. No card needed.
References
- NHS. Understanding calories. nhs.uk.
- 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
- 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, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837. doi:10.1016/S0140-6736(11)60812-X