How many calories should I eat a day has one honest answer: it depends on your size, your age, your sex and how much you move, and a formula turns those four into a number in a few seconds. The six tools below do that and then take the number apart, into the calories your body burns at rest, the protein that keeps muscle, the macros that make up the rest, the water that goes with it and, if you want one, a fasting window; the seventh tile turns the targets into weighed food. Under them is what each figure means, two worked examples, and every guide in this site’s food section.
Nutrition & Diet
Where the Calorie Number Comes From
The calorie calculator uses the Mifflin-St Jeor equation, which a review by the American Dietetic Association found the most accurate of the common formulas for resting metabolism. It starts with your basal metabolic rate, the energy your body spends at complete rest, which is 60 to 70 percent of everything you burn in a day. For a woman that is 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age, minus 161; for a man the last term is plus 5 instead. That resting figure is then multiplied by an activity factor from 1.2 for a desk day with no exercise up to 1.9 for hard daily training, which gives the calories you use in a whole day, your maintenance number.
| Example | At rest (BMR) | Desk day, no exercise | Light exercise 1 to 3 days | Moderate exercise 3 to 5 days |
|---|---|---|---|---|
| Woman, 45, 165 cm, 70 kg | 1,345 | 1,610 | 1,850 | 2,085 |
| Man, 45, 178 cm, 85 kg | 1,740 | 2,090 | 2,395 | 2,700 |
Two things follow from the formula. The number is personal, so a friend’s target says nothing about yours. And it falls with age by about 50 calories a day per decade at the same weight and activity, which is one reason the same plate that held weight steady at 35 does not at 50. The BMR calculator shows the resting figure on its own with the activity table under it.
Eat Under It to Lose, At It to Hold, Over It to Gain
Eat around your maintenance number and your weight stays where it is. Eat about 500 calories a day under it and you lose roughly half a kilogram, a pound, a week, the pace the CDC calls gradual and steady and the one people keep. Cutting harder than that costs muscle and makes the diet harder to hold. The calculator sets the target for either direction and never goes below 1,200 calories a day for a woman or 1,500 for a man, the floors below which a diet needs medical supervision.
Protein First, Then the Rest
Calories decide whether your weight moves; what you eat them as decides what the change is made of. The one macronutrient with a hard target is protein. The official minimum is 0.8 grams per kilogram of body weight a day, which prevents deficiency and no more; the International Society of Sports Nutrition’s position stand puts the range for building and keeping muscle at 1.4 to 2.0 grams per kilogram, spread across three or four meals of 25 to 40 grams, and the tool’s top band for hard dieting runs to 2.2. For the 70 kg woman above that is roughly 100 to 140 grams a day. Protein is also the most filling of the three, which is why a higher protein split makes a deficit easier to keep. Carbohydrate and fat can then flex with what you like to eat: trials find similar fat loss across splits when calories and protein are matched.
Water and the Eating Window
The National Academies put total daily fluid at about 2.7 litres for women and 3.7 for men, of which roughly a fifth arrives in food, so the amount to drink is lower than the headline. Body size and sweat move the figure more than anything else, and the water tool works from about 33 millilitres per kilogram plus an allowance for exercise and heat. Coffee and tea count.
Intermittent fasting changes when you eat, not how much you need. In controlled trials time-restricted eating produced about the same fat loss as ordinary calorie counting, not more; its advantage is that a clock rule is easier for many people to follow than a counting rule, and fewer eating hours tend to mean fewer calories without the arithmetic. It is not for anyone pregnant or breastfeeding, under 18, with a history of disordered eating, or on blood sugar medication, unless a doctor says otherwise.
Between the targets and the plate sits the packet. The five emails below read the Nutrition Facts label one line a day, from the serving size to what the front of the pack is allowed to claim.
Turning the Numbers Into Food
A calorie and protein target is only useful as a plate. The meals page weighs a library of 116 foods to whatever targets you set, each figure traced to its USDA entry, and every meal links to its recipe. The guides below are the whole of this site’s food section, each written against primary sources and dated when it changes.
Protein and Energy
- Ten proteins that lift energy levels
- Protein-rich foods without meat: eight plant-based picks
- Quick high protein snacks under 300 calories
- Anti-inflammatory breakfast ideas for women
- What to eat on night shift, and when to stop eating
- Chia seeds: what happens when you eat them daily
Gut and Inflammation
- Seven anti-inflammatory foods to eat daily
- Twelve anti-inflammatory foods for chronic pain
- Gut healing foods, by mechanism
- How to improve gut health naturally
- High-fiber foods for constipation
- Foods for hair loss in women, by mechanism
Eating With Your Cycle
- Foods for the menstrual phase
- Foods for the follicular phase
- Foods for ovulation
- Foods for the luteal phase
- Food for endometriosis flare-ups
- Foods to eat with the MTHFR mutation
Shopping, Cooking and the Myths
- Shopping for healthy food on a budget
- Healthy recipes that are both delicious and nutritious
- Is your food making you sick? Seven tips for eating well
- Eight health food store myths
- Nutrition myths: why much of what you know may be wrong
New guides land in the Food and Nutrition section, which lists every one with its date.
Frequently Asked Questions
How many calories should a woman eat a day?
It depends on her size, age and activity, so the formula beats any single figure. A 45-year-old woman of 165 cm and 70 kg uses about 1,600 calories on a desk day with no exercise and about 2,100 with moderate exercise most days; the calorie calculator gives your own number. To lose weight, eat about 500 below it and never under 1,200 a day without medical supervision.
How many calories should I eat to lose weight?
About 500 a day under your maintenance number, which loses roughly half a kilogram (a pound) a week. That is the pace the CDC calls gradual and steady. A larger deficit loses muscle as well as fat and is harder to keep; the calculator sets the target and holds the floors of 1,200 for women and 1,500 for men.
Is it better to count calories or macros?
Calories decide whether your weight changes; macros decide what the change is made of. Count calories for the total and set one macro target, protein, at 1.4 to 2.0 grams per kilogram if you train or are dieting. Carbohydrate and fat can follow your preferences: trials show similar fat loss across splits when calories and protein are equal.
Does my calorie need drop after 40?
Yes, slowly. The Mifflin-St Jeor formula subtracts 5 calories a day for every year of age at the same weight, height and activity, so about 50 a day per decade. Muscle loss adds to that, because muscle burns more at rest than fat does, which is why protein and strength training matter more with age.
Do I have to fast to lose weight?
No. In controlled trials time-restricted eating produced about the same fat loss as ordinary calorie counting. Fast if a clock rule suits you better than a counting rule; skip it if you are pregnant, breastfeeding, under 18, have a history of disordered eating or take blood sugar medication, unless your doctor agrees.
Sources
- A new predictive equation for resting energy expenditure in healthy individuals · Mifflin et al., American Journal of Clinical Nutrition
- Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults · Journal of the American Dietetic Association
- Steps for Losing Weight · CDC
- International Society of Sports Nutrition Position Stand: protein and exercise · PMC (NIH)
- Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids · National Academies
- Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate · National Academies
- Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity · JAMA Internal Medicine (PMC)
This page is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment.