WellixHow many calories should I eat a day?
A four-step calculation with every coefficient visible, a calculator that runs it for you, and an honest account of how far to trust the answer.
Short answer
Most adults maintain their weight on roughly 1,600 to 2,800 kcal a day, and lose weight steadily on about 500 kcal a day less than that. Your own number comes from four steps: estimate your resting metabolic rate from sex, age, height and weight; multiply by an activity coefficient; subtract (or add) a daily amount set by how fast you want to change; and never go below 1,500 kcal for men or 1,200 kcal for women.
The calorie calculator runs exactly that calculation in your browser. The rest of this page explains each step, where the numbers come from, and why the result is a starting point rather than a verdict.
Step 1 — Your resting metabolic rate
Resting metabolic rate is the energy your body uses doing nothing: breathing, circulation, keeping warm, repairing tissue. For most people it is 60–75% of everything they burn in a day, which is why the estimate matters more than any workout.
It cannot be measured at home, so it is predicted from the things that drive it. The Harris–Benedict equation, published in 1919 and still the most widely used, takes weight in kilograms, height in centimetres and age in years:1
| Sex | Resting metabolic rate (kcal/day) |
|---|---|
| Men | 65 + (13.7 × kg) + (5 × cm) − (6.8 × age) |
| Women | 655 + (9.6 × kg) + (1.8 × cm) − (4.7 × age) |
A 35-year-old man, 178 cm and 82 kg, comes out at 65 + 1,123 + 890 − 238 = 1,840 kcal. A 35-year-old woman, 165 cm and 65 kg, at 655 + 624 + 297 − 165 = 1,411 kcal.
Two honest caveats. First, the equation was fitted on lean subjects a century ago and overestimates energy expenditure as body fat rises, because fat tissue uses far less energy per kilogram than muscle. Wellix therefore reduces the figure by 5–20% once body mass index passes 27 for men or 26 for women; the direction is well established, the exact steps are our own decision. Second, a 2023 revision of the equation by Pavlidou and colleagues, fitted on modern subjects, placed only about two thirds of men within ±10% of their measured rate — and it was the best of the equations tested.2 Your true resting rate may sit 10% either side of any formula.
Step 2 — Maintenance calories
Multiply the resting rate by an activity coefficient to get the intake at which your weight would hold steady. This is where most online calculators go wrong, because people are optimistic about how active they are and pick a coefficient a step too high.
| Activity | What it means | Coefficient |
|---|---|---|
| Low | Desk job, little deliberate exercise | × 1.25 |
| Medium | On your feet much of the day, or exercise two to three times a week | × 1.35 |
| High | Physical job, or hard training most days | × 1.45 |
The band is deliberately narrow — the conventional 1.2 to 1.9 range produces maintenance figures that, in our experience, most people cannot eat without gaining. Our example man at medium activity maintains on about 1,840 × 1.35 = 2,480 kcal; the woman on about 1,411 × 1.35 = 1,900 kcal.
Step 3 — The deficit (or surplus)
A kilogram of body fat stores roughly 7,700 kcal, so a weekly pace converts to a daily deficit as pace × 7,700 ÷ 7:
| Weekly pace | Daily deficit | Who it suits |
|---|---|---|
| 0.25 kg | 275 kcal | Small amounts to lose, or a long-term habit you want to keep for years |
| 0.5 kg | 550 kcal | The usual recommendation: noticeable, sustainable, protein easy to hit |
| 0.75 kg | 825 kcal | More to lose, and a tolerance for hunger |
| 1 kg | 1,100 kcal | Rarely sustainable; usually clamped by the floor below |
So the example man, losing at 0.5 kg a week, eats about 1,930 kcal; the woman about 1,350 kcal. The 7,700 figure is a linear approximation of a body that is not linear: Hall and colleagues showed in The Lancet that weight responds to a change in intake slowly, with a half-time of about a year, and that heavier people lose more for the same deficit.3 Every calculator that quotes a date uses the same shortcut; treat the timeline as a rough estimate.
Step 4 — The floor
Whatever pace you pick, the target should not fall below 1,500 kcal for men or 1,200 kcal for women. Below that it becomes difficult to meet protein and micronutrient needs from food, and the hunger makes the plan fail. If your chosen pace would breach the floor, reduce the deficit until the target sits on it and accept the slower pace — the calculator does this automatically and tells you the pace you will actually get.
To gain weight, the same logic runs in reverse with a surplus, but Wellix uses the 2023 revised Harris–Benedict equation and the wider 1.2 / 1.55 / 1.9 activity band for it, because the narrow loss-and-maintenance model was calibrated as a whole and does not describe a surplus. A 0.25 kg per week gain — about 275 kcal a day over maintenance — is enough for most people, and going faster mostly adds fat.
What to do with the number
The calculation gives you a hypothesis about your metabolism. Your bodyweight is the experiment that tests it, and it is the only part of this that is measured rather than estimated.
- Eat to the target for two weeks, tracking intake with the same method every day. Consistency of method matters more than which method.
- Weigh yourself daily under the same conditions and take the weekly average. Single readings swing by a kilogram on water alone.
- Compare the change in the average against what the pace predicted.
- Adjust the target by 100–200 kcal in the direction the trend indicates, and repeat.
After two or three cycles you are no longer relying on a formula's guess. You are relying on a measurement of your own body, which is more accurate than any equation can be.
Protein, fat and carbohydrate
Calories decide whether your weight changes; the split decides how you feel while it does. Wellix divides a loss or maintenance target 27.8% protein, 33.3% fat, 38.9% carbohydrate, which for an 1,800 kcal target is about 125 g protein, 67 g fat and 175 g carbohydrate. That protein figure — about 1.6 g per kilogram for an 80 kg person — sits inside the 1.4–2.0 g/kg range the International Society of Sports Nutrition considers sufficient for most exercising people,4 and protein is the macronutrient to protect first in a deficit, because it is what keeps the loss coming from fat rather than muscle. The fat share is higher than many apps set by default; testers, women in particular, rejected the low-fat targets other calculators produce, and that experience is documented on the methodology page.
Where Wellix fits
Wellix runs this calculation during onboarding, from your own measurements and the pace you choose, and shows you the resulting target with the deficit and floor made explicit. It then does the part no calculator can: it logs what you actually eat, from a photograph, so that the two-week comparison above is a glance at a chart rather than a spreadsheet. If you want to see the numbers first, the calculator is the same maths with nothing to install.
Frequently asked questions
How many calories should I eat a day to lose weight?
Your maintenance calories minus a deficit set by your pace: 550 kcal a day for 0.5 kg a week. For most adults that lands between 1,400 and 2,200 kcal a day. Do not go below 1,500 kcal (men) or 1,200 kcal (women) without medical supervision; if your pace would take you there, accept a slower pace instead.
How many calories should I eat to maintain my weight?
Your resting metabolic rate from a Harris–Benedict equation multiplied by an activity coefficient of 1.25 to 1.45. For a 35-year-old man of 178 cm and 82 kg at medium activity that is about 2,480 kcal; for a woman of 165 cm and 65 kg about 1,900 kcal. Check it against two weeks of weight readings and adjust.
Is 1,200 calories a day enough?
It is the floor Wellix will not go below for women, and 1,500 kcal is the floor for men. At that level protein and micronutrients are hard to cover from food, so it should be a limit you reach because your pace pushed you there, not a target you choose. Most people lose weight reliably well above it.
What is a 500 calorie deficit?
Eating about 500 kcal a day less than your maintenance intake, which at roughly 7,700 kcal per kilogram of body fat works out to about 0.45–0.5 kg of loss per week. It is the most commonly recommended pace because it is fast enough to see and slow enough to keep protein and hunger under control.
Why is my calculated number different from other calculators?
Calculators differ in the equation (original or revised Harris–Benedict, Mifflin–St Jeor), the activity coefficients, and whether they correct for body fat. Wellix uses a narrow 1.25–1.45 activity band, so its maintenance figure is usually lower than calculators using the conventional 1.2–1.9 range. Every coefficient is published on the methodology page so you can see exactly what differs.
References
- Harris JA, Benedict FG. A Biometric Study of Basal Metabolism in Man. Carnegie Institution of Washington, Publication No. 279. Washington, DC; 1919.
- Pavlidou E, Papadopoulou SK, Seroglou K, Giaginis C. Revised Harris–Benedict Equation: New Human Resting Metabolic Rate Equation. Metabolites. 2023;13(2):189. doi:10.3390/metabo13020189. pmc.ncbi.nlm.nih.gov/articles/PMC9967803
- Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826–837. PMID: 21872751. pubmed.ncbi.nlm.nih.gov/21872751
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. doi:10.1186/s12970-017-0177-8. pmc.ncbi.nlm.nih.gov/articles/PMC5477153
Wellix provides general nutrition information and is not medical advice. It does not diagnose, treat, or prevent any condition. Calorie and macronutrient targets are estimates produced by predictive equations, and individual requirements vary. Consult a qualified healthcare professional before making significant dietary changes, particularly if you are pregnant or breastfeeding, or have a history of disordered eating, diabetes, kidney disease, thyroid disease, or any other medical condition.
Get the number, then track against it
Wellix sets your target in onboarding and logs each meal from a photo, so the two-week check is a chart, not a spreadsheet.
