WellixHow Wellix calculates your calorie and macro targets
Every equation, every coefficient, and where each one comes from. Most nutrition apps do not publish this.
In short
Wellix sets your daily calorie target in four steps. It estimates your resting metabolic rate from a Harris–Benedict equation, multiplies it by an activity coefficient to obtain your maintenance energy, applies a daily calorie delta derived from the weekly rate of weight change you selected, and clamps the result to a safety floor of 1,500 kcal for men or 1,200 kcal for women. Protein is then set from your body weight, and fat and carbohydrate from that calorie figure.
All of it is published below. Where a coefficient comes from published research, it is cited. Where it comes from our own testing, we say so instead of implying a source that does not exist.
Step 1 — Your resting metabolic rate
Wellix estimates resting metabolic rate with the original 1919 Harris–Benedict equation,1 and it uses the same equation whatever your goal. Your maintenance energy describes your body, not your plan, so losing, maintaining and gaining weight all start from the same number; the goal only changes the delta applied in step 3.
Weight in kilograms, height in centimetres, age in years.
| 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) |
Above a body mass index of 27 for men or 26 for women, Wellix counts only part of your weight. Predictive equations of this family were fitted on largely lean populations and overestimate resting energy expenditure as body fat rises, because fat mass is less metabolically demanding per kilogram than lean mass. Correcting downward is standard practice; the method below is a Wellix decision, not a published coefficient, and we are not going to pretend otherwise.
Weight used = threshold weight + 25% × (your weight − threshold weight)
The threshold weight is what you would weigh at your height with a BMI of 27 (men) or 26 (women); below it, your actual weight is used unchanged. The resulting reduction grows smoothly with BMI:
| Body mass index | Typical reduction in the estimate |
|---|---|
| Below 27 (men) / below 26 (women) | 0% |
| 30 | about 5% |
| 35 | 10–13% |
| 40 | 14–19% |
Because every extra kilogram still adds something to the estimate, a lower weight never produces a higher target — there are no band edges where losing a few hundred grams would raise it.
Step 2 — Your maintenance energy
Wellix multiplies your resting metabolic rate by an activity coefficient to obtain the intake at which your weight would be expected to hold steady, and shows you that number directly. The same coefficients apply whether you are losing, maintaining or gaining weight.
| Activity level | Coefficient |
|---|---|
| Low | × 1.25 |
| Medium | × 1.5 |
| High | × 1.7 |
These coefficients are conventions rather than measurements, and their values are a Wellix decision. They lean slightly cautious, because people tend to be optimistic about how active they are — but not so low that an active person's estimate falls short of what they actually burn, which would make a maintenance target lose weight and a cut run faster than the pace you chose.
Step 3 — Your daily deficit or surplus
Wellix converts the weekly pace you chose into a daily calorie delta at a fixed rate of 7,700 kcal per kilogram of body tissue. Your pace is clamped to between 0.1 and 1.0 kg per week.
Daily delta (kcal) = pace (kg/week) × 7,700 ÷ 7
A 0.5 kg/week loss target therefore produces a 550 kcal daily deficit. Wellix also estimates how many weeks your goal will take, computed from the delta that survives the safety floor in the next step.
Treat the timeline as an approximation. A fixed kcal-per-kilogram conversion is linear, and the body is not. Hall and colleagues showed in The Lancet that the bodyweight response to a change in energy intake is slow — with a half-time of roughly one year — and that people with greater adiposity lose more weight for the same intake change.4 Every calorie app that quotes a target date is using the same approximation. Ours is no worse, and we would rather you knew.
Step 4 — The safety floor
Wellix will never set a daily calorie target below 1,500 kcal for men or 1,200 kcal for women, whatever pace you select. If your chosen pace would breach that floor, Wellix reduces the deficit until the target sits exactly on it, recalculates the pace you will actually achieve, and tells you that it has done so. Your pace is honoured wherever it is safe to honour it, and overridden silently nowhere.
Step 5 — Protein, fat and carbohydrate
For men, Wellix doses protein by body weight, sets fat at a third of your calories, and gives carbohydrate whatever energy remains — the same method whether you are losing, maintaining or gaining. Protein is dosed per kilogram of a reference weight: your goal weight if you are losing, otherwise your current weight — in both cases capped at what you would weigh at a BMI of 24.9, because excess fat mass does not need extra protein.
| Macronutrient | Men | Acceptable range5 |
|---|---|---|
| Protein | 1.8 g/kg losing, 1.6 g/kg maintaining or gaining; +0.2 g/kg from age 50; never more than 35% of calories | 10–35% |
| Fat | 33.3% of calories, at least 0.5 g/kg of reference weight | 20–35% |
| Carbohydrate | The remaining calories | 45–65% |
A 180 cm man eating 2,185 kcal while losing towards 75 kg therefore gets 135 g protein (1.8 × 75), 81 g fat and 229 g carbohydrate. Dosing protein by weight keeps it inside the 1.4–2.0 g/kg/day range the International Society of Sports Nutrition considers sufficient for most exercising individuals.3 A fixed share of calories would not: an active man, who simply eats more, would get far more protein than that range, and a heavy man on a low target far less. If you are lifting seriously in a deficit, the same position stand suggests going higher still, and you should raise the target yourself.
For women
For women, Wellix currently splits a loss or maintenance target across the three macronutrients in a fixed ratio, normalised to exactly 100% of calories:
| Macronutrient | Share of calories | Acceptable range5 |
|---|---|---|
| Protein | 27.8% ÷ 4 kcal/g | 10–35% |
| Fat | 33.3% ÷ 9 kcal/g | 20–35% |
| Carbohydrate | 38.9% ÷ 4 kcal/g | 45–65% |
For a 1,800 kcal target that is roughly 125 g protein, 67 g fat and 175 g carbohydrate — about 1.6 g of protein per kilogram for an 80 kg woman. When a woman's goal is to gain weight, Wellix uses the weight-based method above with two differences: fat is 30% of calories, and protein may take up to 40% of them.
Why Wellix sets fat higher than most calorie apps
Wellix places fat at 33.3% of calories — the upper half of the 20–35% range that the Institute of Medicine considers acceptable for adults.5 This was not a coefficient we picked off a chart. During development, testers — women in particular — consistently rejected the macro splits produced by other calorie apps, which push fat toward the bottom of that range. They reported those targets as impractical to eat and impossible to sustain, and a target nobody follows has an accuracy of zero.
So we moved fat up inside the accepted range rather than out of it, and let carbohydrate absorb the difference. On the women's fixed split carbohydrate lands at 38.9%, below the 45–65% band; on the men's weight-based split it varies, from roughly a third of calories in a deficit to about half at maintenance. That is a deliberate trade, and you can override any target in the app.
Step 6 — Water
Wellix targets what you drink, not your total water intake, because the app logs beverages and a meaningful share of your water arrives inside food. The figures below are a Wellix default, informed by the fluid-requirement ranges used clinically, and we are not citing a source that prescribes this exact schedule.
- 28 ml per kg of bodyweight for men, 25 ml per kg for women.
- Never below 2,000 ml for men or 1,600 ml for women.
- Plus 500 ml at medium activity, or 1,000 ml at high activity.
- Never above 4,000 ml, as a guard against over-drinking.
What a predictive equation can and cannot do
No equation on this page measures your metabolism. They all estimate it, and the estimate carries real spread. In a 2023 study that compared predictive equations against measured resting metabolic rate, the 1919 Harris–Benedict equation Wellix uses placed only about 65% of men within ±10% of their measured value — second only to the authors' own revision, at 67.5%, with the other equations tested doing worse.2
This is the single most useful thing to understand about any calorie target, including the one Wellix gives you. Your starting number is a hypothesis, and your weight trend is the experiment. Track your intake and your weight for two weeks, compare the change against what your target predicted, and adjust by 100–200 kcal in the direction the trend indicates. After two or three cycles you are no longer relying on a formula's guess about your metabolism — you are relying on a measurement of it. This is why Wellix tracks your weight trend alongside your intake rather than treating the target as settled.
Three further limits worth stating plainly. The equations assume an adult with no condition that alters energy expenditure — pregnancy, breastfeeding, thyroid disease, kidney disease and many medications all change the answer and none of them are inputs to our model. If you have not told Wellix your age, height, weight or sex, it substitutes a default (age 30, 170 cm, 70 kg for men or 60 kg for women), and every default degrades your targets. And users recorded as neither male nor female are computed with the male equation, which is a limitation of sex-split equations rather than a statement about anyone.
How the food side works
The targets above are what you aim at. The other half of the system is what you actually ate, which Wellix estimates from a photograph using a vision model — an estimate with its own error characteristics, which we cover with the same candour in how accurate are AI calorie counting apps.
Frequently asked questions
What formula does Wellix use to calculate calories?
Wellix estimates resting metabolic rate with the original 1919 Harris–Benedict equation for every goal — counting only a quarter of any weight above a BMI of 27 for men or 26 for women — multiplies it by an activity coefficient of 1.25, 1.5 or 1.7 to obtain maintenance energy, then applies a daily calorie delta derived from your chosen weekly pace at 7,700 kcal per kilogram. The result is clamped to a floor of 1,500 kcal for men or 1,200 kcal for women.
Why does Wellix give me more fat than other calorie apps?
Wellix sets fat at 33.3% of calories, in the upper half of the 20–35% of energy that the Institute of Medicine considers an acceptable range for adults. During development our testers, women especially, found the low-fat targets produced by other calorie apps impractical to eat and impossible to sustain. We moved fat up inside the accepted range rather than outside it, and carbohydrate absorbs the difference.
What is the lowest calorie target Wellix will give me?
Wellix will never set a daily target below 1,500 kcal for men or 1,200 kcal for women. If the weight-loss pace you selected would require going below that floor, Wellix reduces the deficit so the target sits exactly on the floor, recalculates the pace you will actually achieve, and tells you it has done so.
How accurate is a calculated calorie target?
It is an estimate with real spread. In a 2023 study comparing predictive equations against measured resting metabolic rate, the 1919 Harris–Benedict equation that Wellix uses placed only about 65% of men within ±10% of their measured value, second only to a newly revised version at 67.5%. Treat your starting target as a hypothesis and your two-week weight trend as the experiment that corrects it.
Why does Wellix reduce my metabolic rate estimate when my BMI is high?
Because Harris–Benedict equations were fitted on largely lean populations and overestimate resting energy expenditure as body fat rises, since fat mass burns fewer calories per kilogram than lean mass. Above a BMI of 27 for men or 26 for women, Wellix counts only 25% of the weight above that threshold, which lowers the estimate by about 5% at BMI 30 and 14–19% at BMI 40. The reduction rises smoothly, so a lower weight never produces a higher target. The direction of that correction is well established; the method and the 25% share are a Wellix decision rather than a published coefficient, and we label them as such.
How does Wellix decide my protein target?
For men, protein is dosed by weight: 1.8 g per kilogram of goal weight when losing, and 1.6 g per kilogram of current weight when maintaining or gaining — the weight capped at what you would weigh at a BMI of 24.9 — plus 0.2 g/kg from age 50, and never more than 35% of calories. That keeps it inside the 1.4–2.0 g/kg/day range the International Society of Sports Nutrition considers sufficient for most exercising individuals. For women, protein is currently 27.8% of a loss or maintenance target, and 1.6 g per kilogram of the same capped reference weight when gaining.
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
- 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
- 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
- Institute of Medicine. Dietary Reference Intakes: Acceptable Macronutrient Distribution Ranges. Summary Table 5. National Academies Press. ncbi.nlm.nih.gov/books/NBK56068
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.
Targets you can inspect, from a log that takes a photo
Wellix computes the numbers above from your body and your goal, then shows its work.
