On this page
Key takeaways
- Typical needs: about 1,600 to 2,400 calories a day for adult women and 2,000 to 3,000 for adult men, depending on age and activity, according to the US Dietary Guidelines.2
- Your own estimate: Mifflin-St Jeor for resting burn, times an activity factor of 1.2 to 1.9. It is the most accurate of the common equations, but still only a starting point.3, 4
- Safe pace: 1 to 2 lb (0.5 to 1 kg) a week, which usually means eating about 500 calories a day below maintenance.6, 7
- The target moves. A lighter body burns less, and metabolism adapts beyond that, so a number set once will stop working. Recheck it against your weight trend every week or two.5, 8
Where your calories go
Total daily energy expenditure has three parts. Resting (basal) metabolism is the energy your organs use to keep you alive, and it is the largest share for most people, roughly 60 to 70 percent in sedentary adults. Physical activity, which includes workouts and every other movement in a day, is the most variable part. The thermic effect of food, the cost of digesting what you eat, adds about 10 percent.1
Because resting metabolism is tied to body size, sex and age, any good estimate starts there and then scales for how much you move.
Step 1: estimate your resting burn
The Mifflin-St Jeor equation, published in 1990, is the one most dietitians use.3 When the Academy of Nutrition and Dietetics compared the popular prediction equations against measured metabolic rates, Mifflin-St Jeor was the most reliable, landing within 10 percent of the measured value in roughly seven to eight out of ten adults, in both non-obese and obese groups.4
| Sex | Resting metabolic rate (calories per day) |
|---|---|
| Men | 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5 |
| Women | 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161 |
Two caveats. The equation was built from averages, so it cannot see how much muscle you carry, and a very muscular person will burn more than it predicts. And "within 10 percent" still means an individual estimate can be off by 150 to 300 calories a day. That is why the last step in this guide matters more than the first.
Step 2: multiply by your activity level
The Dietary Reference Intakes describe four physical activity levels, expressed as a multiple of resting metabolism: sedentary (1.0 to 1.39), low active (1.4 to 1.59), active (1.6 to 1.89) and very active (1.9 to 2.5).1 The single-number multipliers that calculators use fall inside those bands.
| How you move most weeks | Common multiplier |
|---|---|
| Desk job, little deliberate exercise | 1.2 |
| Light exercise 1 to 3 days a week, or a job on your feet | 1.375 |
| Moderate exercise 3 to 5 days a week | 1.55 |
| Hard exercise 6 to 7 days a week, or a physical job plus training | 1.725 |
Most people pick a level too high. Three gym sessions a week on top of a desk job is "light" to "moderate", not "very active". If in doubt, choose the lower band; the weekly weigh-in will correct you in the right direction.
Step 3: choose a deficit you can keep
Both the US CDC and the UK NHS describe a safe rate of weight loss as 1 to 2 pounds, or 0.5 to 1 kilogram, a week.6, 7 In practice that is a deficit of about 500 calories a day at the lower end, and up to 1,000 a day at the upper end, which few people can sustain and which often pushes intake below safe minimums.
The familiar "3,500 calories equals a pound" rule overstates what a deficit will do over time. As you get lighter you burn less, so the same deficit shrinks. A 2011 analysis in The Lancet proposed a more realistic rule: every permanent 10-calorie-a-day reduction leads to about 1 pound (0.45 kg) of eventual weight change, with half of that reached in roughly a year.5
The NHS classes anything under about 800 calories a day as a very-low-calorie diet, to be followed only under medical supervision.7 Below roughly 1,200 calories a day for women and 1,500 for men it becomes hard to cover protein, fiber and micronutrient needs, which is why clinical programs rarely go lower without a clinician involved. If your deficit math lands below those numbers, lower the deficit, not the floor.
Two worked examples
| Person | Resting rate | Maintenance | Target for about 0.5 kg a week |
|---|---|---|---|
| Woman, 35, 165 cm, 70 kg, light activity (1.375) | 700 + 1,031 − 175 − 161 = 1,395 | 1,395 × 1.375 = 1,918 | 1,918 − 500 ≈ 1,400 |
| Man, 45, 178 cm, 95 kg, moderate activity (1.55) | 950 + 1,113 − 225 + 5 = 1,843 | 1,843 × 1.55 = 2,856 | 2,856 − 500 ≈ 2,350 |
Notice how close the first example sits to the 1,200 floor. For a smaller or older person, a 500-calorie deficit may need to become 300 to 400, with a slower expected pace to match.
Why the number changes as you lose weight
Two things happen. First, the arithmetic: a body that weighs 10 kg less has a lower resting rate and costs less to move, so maintenance drops by a few hundred calories. Second, metabolism adapts beyond what the smaller body size predicts. In the best-known study of this effect, people who had lost large amounts of weight were still burning about 500 calories a day less than expected for their body composition six years later.8 Most people see a much smaller effect, but the direction is the same: the deficit you started with will quietly shrink.
The practical answer is not to recalculate the equation, which still cannot see your individual metabolism, but to measure. If your weight trend over two to four weeks is flat on a target that should produce a loss, your real maintenance is lower than the estimate, and the target comes down a step.
Why counting is harder than it looks
In a classic New England Journal of Medicine study, people who were convinced they could not lose weight on a low-calorie diet were found to be under-reporting what they ate by an average of 47 percent and over-reporting their activity by 51 percent, without meaning to.9 Portion sizes, cooking oil, drinks and weekend meals are the usual blind spots.
The good news is that the act of tracking works even when the numbers are imperfect. A systematic review of self-monitoring studies found consistent associations between logging food, activity or weight and successful weight loss.10 Consistency beats precision: a rough log of every day tells you more than a perfect log of three days.
When a deficit is the wrong tool
- Pregnancy and breastfeeding. Energy needs go up, not down. Do not aim for a deficit without your doctor or midwife.
- Children and teenagers. Needs are tied to growth; this adult method does not apply.
- Diabetes treated with insulin or sulfonylureas. Cutting carbohydrate and calories changes medication needs and raises the risk of low blood sugar. Adjust with your care team.
- A history of disordered eating. Counting can be a trigger. A registered dietitian can suggest safer approaches.
- Kidney disease, heart failure or recent surgery. Protein and fluid limits may override general calorie advice.
Questions people ask
Is 1,200 calories a day enough?
For most adults, 1,200 calories is below what the body burns at rest and makes it hard to meet protein, fiber and micronutrient needs. Clinical programs usually treat it as the lowest level to use without supervision, and anything under about 800 calories a day is a very-low-calorie diet that the NHS says should only be followed under medical supervision.7 A moderate deficit of about 500 calories below maintenance is the usual recommendation.
How many calories do I need to cut to lose 1 kg a week?
Roughly 1,000 calories a day below maintenance, which is the upper end of what the CDC and NHS consider a safe pace.6, 7 For many people that deficit is too large to sustain and pushes intake below safe minimums, so a 500-calorie deficit aimed at about 0.5 kg a week is the more common target.
Should I eat back the calories I burn exercising?
Only if your target was built on a sedentary activity level. If you chose a multiplier that already includes your workouts, adding exercise calories on top counts them twice. Wearable and machine estimates of calories burned are also often high, so a safer approach is to keep the target fixed and let your weekly weight trend tell you whether it is right.
Is my BMR the number of calories I should eat?
No. Basal, or resting, metabolic rate is what you burn lying still. Total daily energy expenditure adds everyday movement, exercise and the energy used to digest food, and is usually 1.2 to 1.9 times BMR.1 Eating at BMR is a large deficit, not maintenance.
How accurate are calorie calculators?
The best equation, Mifflin-St Jeor, lands within 10 percent of measured resting metabolic rate in roughly seven to eight out of ten adults,4 so an individual estimate can easily be off by 150 to 300 calories a day. Treat the calculator as a starting point and adjust from your real weight trend over two to four weeks.
How Calobook does it
Calobook starts exactly where this guide does: your answers during setup feed a resting-rate estimate, an activity level and a pace you choose, with a floor on calories and a cap on weekly pace for your body weight. Then it does the part a calculator cannot. Every week it compares the calories you actually logged with how your weight actually moved, measures your real burn from that, and retunes your calorie and macro targets inside safe limits. Nothing starts over, and the check-in screen lists every reason for the change.
Three minutes of questions, a plan built around your body, and a weekly check-in that measures instead of guessing.
Sources
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005), chapter 5, Energy.
- US Department of Agriculture and Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025, Appendix 2, Estimated Calorie Needs per Day.
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 2005.
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011.
- Centers for Disease Control and Prevention. Steps for Losing Weight.
- NHS. Obesity: Treatment.
- Fothergill E, et al. Persistent metabolic adaptation 6 years after "The Biggest Loser" competition. Obesity, 2016.
- Lichtman SW, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. New England Journal of Medicine, 1992.
- Burke LE, Wang J, Sevick MA. Self-monitoring in weight loss: a systematic review of the literature. Journal of the American Dietetic Association, 2011.
This article is general nutrition information written by the Calobook team from the sources listed above. It is not medical advice and does not replace a consultation with a doctor or registered dietitian. If you are pregnant, breastfeeding, under 18, or managing a medical condition, talk to a professional before changing your diet. Last reviewed October 17, 2026.