How many calories per day, by the evidence

1. 01

   The population starting point: 1,600-2,400 for women, 2,000-3,000 for men

   The Dietary Guidelines for Americans estimate that adult women need about 1,600-2,400 kcal/day and adult men about 2,000-3,000, with the low end for older, sedentary people and the high end for young, active ones (USDA and HHS, 2020-2025). These are averages for a healthy weight, not personal prescriptions, and the range is deliberately wide because age, body size, and activity move the number by hundreds of calories. Use the band to sanity-check a calculator result, not as your target: a sedentary 60-year-old woman near 1,600 and an active 25-year-old man near 3,000 are both normal.

2. 02

   Your real number: resting burn times an activity factor

   Your daily requirement is your total daily energy expenditure (TDEE), which is basal metabolic rate multiplied by an activity factor. BMR is what you burn at complete rest and makes up 60-70 percent of the total. The common multipliers are ~1.2 for sedentary, 1.375 for light activity (1-3 days of exercise), 1.55 for moderate (3-5 days), and 1.725 for very active (6-7 days). So a person with a 1,650 kcal BMR needs about 1,980 kcal sedentary but 2,560 kcal if very active. The activity factor, not the BMR, is what most people get wrong.

3. 03

   Estimate BMR with the Mifflin-St Jeor equation

   The most validated bedside estimate of resting metabolic rate is Mifflin-St Jeor (Mifflin et al. 1990). For men: 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age in years, plus 5. For women: the same, but minus 161 at the end. A 70 kg, 175 cm, 35-year-old man works out to about 1,649 kcal at rest; a 60 kg, 165 cm, 35-year-old woman to about 1,320. The older Harris-Benedict equation tends to run 5 percent high; Mifflin-St Jeor is the current default in dietetics because it tracks measured RMR more closely.

4. 04

   The activity multiplier is where estimates break

   Picking the activity factor is the biggest source of error. Most people overrate structured exercise, which for a typical gym-goer adds only 200-400 kcal a session, and underrate non-exercise activity thermogenesis (NEAT): the walking, standing, fidgeting, and chores that can vary by 400-800 kcal/day between two similar people (Levine 2004). A desk job with a car commute is genuinely sedentary (1.2) even if you train three times a week; a nurse on their feet all shift may sit near 1.55 without any formal exercise. When unsure, choose the lower factor and let the scale correct upward.

5. 05

   Losing or gaining: about 500 kcal a day per half-kilo a week

   To change weight you set a gap against your TDEE. A deficit of roughly 500 kcal/day targets about 0.45 kg (1 lb) of loss per week, and a 500 kcal surplus the reverse, from the rough figure that a pound of body fat stores about 3,500 kcal. Keep the deficit moderate: cutting more than about 20-25 percent below maintenance tends to cost muscle and drive hunger without speeding fat loss much. A reasonable floor is not eating below your BMR for long. Faster is not better here; the moderate deficit is the one people actually sustain.

6. 06

   The four pieces of your daily burn

   TDEE has four components. BMR is the largest at 60-70 percent. The thermic effect of food, the energy spent digesting, is a steady ~10 percent and runs higher on protein than on fat or carbohydrate. Exercise activity is the piece people fixate on but is often the smallest and most overestimated. NEAT, everything you do that is not formal exercise, is the most variable and the reason two people of the same size can differ by 500 kcal/day. This is why raising daily steps often beats adding cardio sessions for changing the total.

7. 07

   The calculator is a starting point, not a verdict

   Every equation carries a wide error bar, because measured resting metabolism varies by 5-10 percent between people of identical size, and activity varies far more. The honest method is empirical: take the estimate, eat at that number consistently for two weeks, track the weight trend against a daily or near-daily weigh-in, and adjust by 100-200 kcal based on what the scale actually did, not on what the calculator predicted. Weight also swings day to day with water, salt, and glycogen, so judge the two-week trend line, not any single morning.

What people ask us next.

Q01

How many calories should I eat a day?

For weight maintenance, most adult women need about 1,600-2,400 kcal/day and most men 2,000-3,000, with the low end for older, sedentary people and the high end for young, active ones (USDA and HHS, 2020-2025). Your personal number is your basal metabolic rate, estimated with the Mifflin-St Jeor equation, multiplied by an activity factor of roughly 1.2 to 1.725. Treat any figure as a starting estimate and confirm it against two weeks of scale data.

Q02

How do I calculate my calorie needs?

Estimate basal metabolic rate with Mifflin-St Jeor: for men, 10 times weight in kg plus 6.25 times height in cm minus 5 times age plus 5; for women the same but minus 161. Then multiply by an activity factor: ~1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very active. The result is your total daily energy expenditure, the calories to maintain weight. Subtract about 500 for weight loss or add that much to gain.

Q03

How many calories should I eat to lose weight?

A deficit of about 500 kcal/day below your maintenance number targets roughly 0.45 kg (1 lb) of loss per week, based on the rule that a pound of fat stores about 3,500 kcal. Keep the cut moderate, generally no more than 20-25 percent below maintenance, and avoid eating below your resting metabolic rate for long. As you lose weight your maintenance number falls, so the deficit shrinks and has to be reset every few kilos.

Q04

Why am I not losing weight in a calorie deficit?

The usual reason is that the deficit is smaller than it looks: calorie labels and portion estimates commonly run 20-25 percent low, activity multipliers are overrated, and metabolic adaptation lowers your burn as you lose. Water, salt, and glycogen shifts also mask fat loss for days at a time. The fix is to weigh the two-week trend rather than a single morning, tighten portion accuracy, and cut another 100-200 kcal only if the trend is genuinely flat.

Q05

How many calories do I burn at rest?

Your basal metabolic rate, the energy spent at complete rest, is 60-70 percent of your total daily burn. For a 70 kg, 175 cm, 35-year-old man it is about 1,650 kcal; for a 60 kg, 165 cm woman of the same age about 1,320, using Mifflin-St Jeor. Larger, taller, younger, and more muscular bodies burn more at rest. This resting figure, not your workouts, is the biggest single piece of the calorie total.

Q06

Do I have to count calories to lose weight?

No. Counting works because it makes energy balance visible, but the same deficit can be reached by controlling portions, prioritizing protein and fiber to blunt hunger, and cutting the highest-calorie liquids and fried foods. Many people do best counting for two to four weeks to learn portion sizes, then maintaining the habits without daily logging. What is not optional is the energy gap itself: weight loss still requires eating less than you burn.