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 Most nutrition apps do not publish this.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, fat and carbohydrate are then split 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 a Harris–Benedict equation, using the 1919 original1 when your goal is to lose or maintain weight, and the 2023 revision by Pavlidou and colleagues2 when your goal is to gain. These are two models for two different problems: the loss-and-maintenance model is calibrated as a whole — equation, body-composition adjustment, activity band and macro split together — and it does not describe an energy surplus, so weight gain uses the newer published equation instead.
Losing or maintaining weight
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) |
Wellix then reduces that figure according to your body mass index. 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 specific schedule below is a Wellix decision, not a published coefficient, and we are not going to pretend otherwise.
| Body mass index | Reduction applied |
|---|---|
| Below 27 (men) / below 26 (women) | 0% |
| Up to 30 | 5% |
| 30 to under 35 | 10% |
| 35 to under 40 | 15% |
| 40 and above | 20% |
Gaining weight
Height is in metres here, and no body-composition reduction is applied.2
| Sex | Resting metabolic rate (kcal/day) |
|---|---|
| Men | (9.65 × kg) + (573 × m) − (5.08 × age) + 260 |
| Women | (7.38 × kg) + (607 × m) − (2.31 × age) + 43 |
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 loss-and-maintenance path uses a deliberately narrow, conservative band; the gain path uses the wider conventional one.
| Activity level | Lose / maintain | Gain |
|---|---|---|
| Low | × 1.25 | × 1.2 |
| Medium | × 1.35 | × 1.55 |
| High | × 1.45 | × 1.9 |
Both bands are conventions rather than measurements. The narrower one produces a lower maintenance estimate, and therefore a more cautious calorie target, for the people most likely to be cutting.
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
When you are losing or maintaining weight, Wellix splits your calorie target across the three macronutrients in a fixed ratio and normalises it to exactly 100% of your 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.
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. Carbohydrate consequently lands at 38.9%, below the 45–65% band, because the energy has been reallocated to protein and fat. That is a deliberate trade, it is visible in the table above, and you can override any target in the app.
The resulting protein figure — about 1.6 g per kilogram for an 80 kg person on 1,800 kcal — sits inside the 1.4–2.0 g/kg/day range the International Society of Sports Nutrition considers sufficient for most exercising individuals.3 If you are lifting seriously in a deficit, the same position stand suggests going higher still, and you should raise the target yourself.
When your goal is to gain weight
On the gain path Wellix doses protein and fat per kilogram of a reference weight — your current weight, capped at whatever you would weigh at a BMI of 24.9 — rather than raw bodyweight, which over-doses heavier users and squeezes carbohydrate toward zero.
- Protein — 1.6 g per kg of reference weight, plus 0.2 g/kg if you are 50 or older, as a guard against age-related muscle loss. Never more than 40% of your calories.
- Fat — 30% of calories, with an essential-fat floor of 0.5 g per kg of reference weight.
- Carbohydrate — the remaining calories, with a 50 g floor.
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 the study that introduced the revised equation Wellix uses for weight gain, that equation — the best performer the authors tested — placed only about 67.5% of men within ±10% of their measured resting metabolic rate.2 Every other equation did worse.
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 a Harris–Benedict equation — the 1919 original for weight loss and maintenance, and the 2023 revision by Pavlidou et al. for weight gain — multiplies it by an activity coefficient between 1.2 and 1.9 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 the study introducing the revised Harris–Benedict equation that Wellix uses for weight gain, that equation placed only about 67.5% of men within ±10% of their measured resting metabolic rate, and it outperformed the alternatives tested. 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. Wellix applies a reduction of 5% to 20% depending on BMI. The direction of that correction is well established; the specific step sizes are a Wellix decision rather than a published coefficient, and we label them as such.
How does Wellix decide my protein target?
If you are losing or maintaining weight, protein is 27.8% of your calorie target — about 1.6 g per kilogram for an 80 kg person eating 1,800 kcal, which sits inside the 1.4–2.0 g/kg/day range the International Society of Sports Nutrition considers sufficient for most exercising individuals. If you are gaining weight, protein is dosed at 1.6 g per kilogram of a reference weight capped at BMI 24.9, plus 0.2 g/kg if you are 50 or older.
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.
