WellixCalorie calculator
How many calories you should eat a day to lose, maintain or gain weight — plus protein, carbohydrate and fat targets. The formulas are published in full below, and they are the ones the Wellix app uses.
How it works
The calculator estimates your resting metabolic rate with a Harris–Benedict equation, multiplies it by an activity coefficient to get the calories at which your weight would hold steady, then applies a daily deficit or surplus derived from the weekly pace you choose — clamped to a safety floor of 1,500 kcal for men and 1,200 kcal for women.
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Your daily targets
- Maintenance calories
- kcal
- Daily deficit
- kcal
- Resting metabolic rate
- kcal
- Body mass index
The formulas, in full
Every coefficient below is the one the Wellix app uses. Where a number comes from published research it is cited on the methodology page; where it is our own decision, we say so there.
1. Resting metabolic rate
For weight loss and maintenance, the original Harris–Benedict equation (weight in kg, height in cm, age in years):
- Men: 65 + 13.7 × kg + 5 × cm − 6.8 × age
- Women: 655 + 9.6 × kg + 1.8 × cm − 4.7 × age
The result is reduced by 5–20% as body mass index rises above 27 (men) or 26 (women), because these equations were fitted on lean populations and overestimate energy expenditure at higher body fat. For weight gain, the 2023 revised Harris–Benedict equation by Pavlidou and colleagues is used instead (height in metres): men 9.65 × kg + 573 × m − 5.08 × age + 260, women 7.38 × kg + 607 × m − 2.31 × age + 43.
2. Maintenance calories
Resting metabolic rate × activity coefficient. Loss and maintenance use a deliberately narrow band — 1.25 / 1.35 / 1.45 for low, medium and high activity — because people overestimate how active they are. Weight gain uses the wider conventional band, 1.2 / 1.55 / 1.9.
3. Daily deficit or surplus
Weekly pace (kg) × 7,700 ÷ 7. A 0.5 kg per week loss is a 550 kcal daily deficit. The target is never set below 1,500 kcal for men or 1,200 kcal for women; if your pace would breach that floor, the deficit is reduced and the achievable pace recalculated.
4. Protein, fat and carbohydrate
For loss and maintenance the calorie target is split 27.8% protein, 33.3% fat, 38.9% carbohydrate (a 25:30:35 ratio normalised to 100%), at 4, 9 and 4 kcal per gram. For weight gain, protein is dosed at 1.6 g per kg of a reference weight capped at BMI 24.9 (plus 0.2 g/kg from age 50), fat at 30% of calories, and carbohydrate takes the remainder.
5. Drinking water
28 ml per kg for men and 25 ml per kg for women, with floors of 2.0 L and 1.6 L, plus 500 ml at medium activity or 1,000 ml at high activity, capped at 4 L. This is what you drink, not total water — food supplies roughly a fifth of the total.
Related
- How Wellix calculates your calorie and macro targets
- Calories in foods: per 100 g and per serving
- How to track calories without weighing your food
- How accurate are AI calorie counting apps?
Frequently asked questions
How many calories should I eat a day to lose weight?
Your maintenance calories minus a deficit set by how fast you want to lose. A 0.5 kg per week pace is a 550 kcal daily deficit; for most adults that lands between 1,400 and 2,200 kcal a day. Never go below 1,500 kcal (men) or 1,200 kcal (women) without medical supervision — the calculator applies that floor automatically.
How accurate is a calorie calculator?
It is an estimate with real spread. Predictive equations place roughly two thirds of people within ±10% of their measured resting metabolic rate, and the activity coefficient is a bigger guess still. Treat the result as a starting hypothesis, then adjust it against your two-week weight trend.
What is a calorie deficit?
Eating fewer calories than your body uses. The difference is made up from stored energy, mostly body fat. Wellix converts weekly pace to a daily deficit at 7,700 kcal per kilogram, so 0.5 kg per week is about 550 kcal per day.
How much protein should I eat?
On the loss and maintenance targets above, protein is 27.8% of calories — about 1.6 g per kilogram of bodyweight for an 80 kg person on 1,800 kcal, inside the 1.4–2.0 g/kg range the International Society of Sports Nutrition considers sufficient for most exercising people. If you lift seriously in a deficit, go towards the top of that range.
Why does the calculator reduce my resting metabolic rate at a higher BMI?
Harris–Benedict equations were fitted on largely lean populations and overestimate energy expenditure as body fat rises, because fat mass burns fewer calories per kilogram than lean mass. The direction of the correction is well established; the exact 5–20% steps are a Wellix decision and are labelled as such on the methodology page.
Does Wellix use this exact calculation?
Yes. The app computes your targets from the same equations, coefficients, floors and macro split shown on this page, and shows you the resulting numbers during onboarding. The methodology page documents every source.
Sources
Equations: Harris JA, Benedict FG (1919); Pavlidou E et al., Metabolites 2023;13(2):189; protein range: Jäger R et al., ISSN Position Stand, J Int Soc Sports Nutr 2017;14:20. Activity coefficients, BMI correction steps and the macro split are Wellix decisions documented on the methodology page.
Wellix provides general nutrition information and is not medical advice. 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.
Now track against it
Wellix sets these targets for you in onboarding, then logs your meals from a photo so you can see how each day lands against them.
