How we count every number
Every target in Flawless is an estimate produced by a published equation from the numbers you entered — your age, weight, height, sex and activity. It is not a measurement and it is not medical advice.,The equations below were built on healthy adults. Talk to a doctor or a registered dietitian before you act on any of these numbers — and especially if you are under 18, pregnant or breastfeeding, or managing a medical condition such as diabetes, kidney or heart disease, or an eating disorder.
Most fitness apps motivate. This page is the other thing: every number the app shows you, the formula behind it, and the study it comes from. If we cannot show you the arithmetic, the number does not go in the app.
Daily calories
Your calorie target is your resting metabolism multiplied by an activity factor, then adjusted for your goal.
Resting metabolism uses the Mifflin–St Jeor equation, which was built by measuring 498 healthy adults with indirect calorimetry and explains about 71% of the variation between people.
The activity factors (1.2 to 1.9) are the convention used with this equation rather than a value taken from one study. For reference, the FAO/WHO/UNU framework groups adults into 1.40–1.69 (sedentary or light), 1.70–1.99 (moderately active) and 2.00–2.40 (vigorously active); the app's lowest factors deliberately sit below that floor for people who barely move.
Because it is a population average, your real expenditure can differ by several hundred kilocalories. If your weight does not move the way the target predicts after two or three weeks, trust the scale over the formula.
BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5 (men) / - 161 (women)
TDEE = BMR x activity factor (1.2 / 1.375 / 1.55 / 1.725 / 1.9)Sources (2)
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
- FAO/WHO/UNU. Human Energy Requirements. Report of a Joint Expert Consultation. Rome, 2004 — physical activity level (PAL) categories.
Losing and gaining weight
Choosing Lose subtracts 500 kcal a day. The 2013 AHA/ACC/TOS obesity guideline prescribes exactly this: a 500 or 750 kcal daily energy deficit, which for most people means roughly 0.5 kg a week.
Choosing Gain adds 350 kcal a day. The surplus is deliberately small: in trials on trained athletes, a larger surplus added more fat without adding proportionally more muscle.
Maintain adds nothing.
kcal = TDEE - 500 (lose) / + 0 (maintain) / + 350 (gain)Sources (3)
- Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults. Circulation. 2014;129(25 Suppl 2):S102–S138.
- Slater G, Phillips SM. Nutrition guidelines for strength sports: sprinting, weightlifting, throwing events, and bodybuilding. J Sports Sci. 2011;29(Suppl 1):S67–S77.
- Garthe I, Raastad T, Refsnes PE, Sundgot-Borgen J. Effect of nutritional intervention on body composition and performance in elite athletes. Eur J Sport Sci. 2013;13(3):295–303.
Protein
The app targets 2.2 g of protein per kilogram of body weight.
A meta-analysis of 49 studies and 1,863 people found that gains in muscle and strength from protein flatten out at about 1.62 g/kg/day, with the confidence interval reaching up to 2.2 g/kg/day. The app deliberately uses the top of that interval, so a heavy training week is covered rather than under-fed.
For context, the ISSN position stand puts the general range at 1.4–2.0 g/kg/day for exercising adults, and 2.3–3.1 g/kg/day for trained people eating in a calorie deficit.
Higher protein is not automatically better, and people with kidney disease should not follow these numbers without a doctor.
protein (g) = weight (kg) x 2.2Sources (2)
- Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376–384.
- 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.
Fat
Fat is set at 25% of your calorie target, which sits in the middle of the Acceptable Macronutrient Distribution Range of 20–35% of energy for adults, published by the Institute of Medicine.
Fat carries 9 kcal per gram, which is why the gram number looks small next to carbs.
fat (g) = kcal x 0.25 / 9Carbohydrates
Carbohydrates are whatever calories are left once protein and fat are taken out. They are not targeted directly.
This keeps the three macros adding up to your calorie target exactly, and it usually lands inside the Acceptable Macronutrient Distribution Range of 45–65% of energy.
carbs (g) = (kcal - protein x 4 - fat x 9) / 4Fibre
Fibre is set at 0.35 g per kilogram of body weight, which for most adults lands between 25 and 35 g a day.
EFSA considers 25 g a day adequate for normal bowel function in adults and notes further benefit above that. The Institute of Medicine expresses the same idea per energy: 14 g per 1,000 kcal.
fibre (g) = weight (kg) x 0.35BMI
Body mass index is your weight divided by your height squared. The bands come from the World Health Organization: below 18.5 underweight, 18.5–24.9 normal, 25.0–29.9 overweight, 30.0 and above obesity.
BMI does not know the difference between muscle and fat, and it says nothing about where fat sits on your body. Trained, muscular people frequently read as overweight while being nothing of the sort. Treat it as one crude number among several, never as a diagnosis.
BMI = weight (kg) / height (m)^2FFMI (fat-free mass index)
FFMI works like BMI, but only with the part of your weight that is not fat — muscle, bones, organs and water. It first takes your body fat percentage away from your weight, then divides the lean mass by your height squared. That makes it more useful than BMI for people who train, because muscle does not push it into an overweight band.
The study that introduced it added a small correction so that people of different heights can be compared as if they were 1.80 m tall; the big number in the calculator is this normalised value. In that study, 74 male athletes who had never used anabolic steroids did not go above a normalised FFMI of 25.0. The study measured men only.
The result is only as good as your body fat figure. A body fat estimate that is 3 points off moves FFMI by up to about one point, so treat it as a trend to follow, not a verdict.
lean mass (kg) = weight (kg) × (1 − body fat % / 100)
FFMI = lean mass (kg) / height (m)^2
normalised FFMI = FFMI + 6.3 × (1.80 − height (m))Weekly volume per muscle
The card counts your working sets from the last 7 days: every ticked set except warm-ups. Cardio, stretching and mobility are left out.
The muscle an exercise targets gets one set; a muscle that only assists gets half a set. A 2026 meta-regression of 67 studies found that counting assisting sets as half fits the results best.
The marks at 5 and 10 sets are the bands from a 2017 meta-analysis (under 5, 5–9 and 10 or more sets per muscle a week): more weekly sets went with more muscle growth. More volume keeps helping, but each extra set adds a little less — there is no single magic number, and recovery matters too.
sets(muscle) = Σ working sets where muscle is the target × 1
+ Σ working sets where muscle assists × 0.5
working set = ticked, not a warm-up · window = last 7 daysSources (2)
- Schoenfeld BJ, Ogborn D, Krieger JW. Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. J Sports Sci. 2017;35(11):1073–1082.
- Pelland JC, Remmert JF, Robinson ZP, Hinson SR, Zourdos MC. The Resistance Training Dose Response: Meta-Regressions Exploring the Effects of Weekly Volume and Frequency on Muscle Hypertrophy and Strength Gains. Sports Med. 2026;56(2):481–505.
Water
This one is different from the rest, and it is worth saying plainly: the hydration goal is our own estimate, not an equation taken from a published study.
It starts from your lean body mass, allows 40 ml per kilogram of lean mass and 20 ml per kilogram of the rest, nudges the result slightly for age and height, then caps it between 1.5 and 4 litres and rounds it to glasses of 250 ml.
For an external reference point, EFSA sets adequate total water intake at 2.0 litres a day for women and 2.5 litres for men — counting all drinks plus the water in food, not just what you log here.
Thirst, urine colour and your climate tell you more than any formula. Some conditions require fluid restriction, and there the number in this app does not apply at all.
ml = lean mass (kg) x 40 + fat mass (kg) x 20, adjusted for age and height,
limited to 1500-4000 ml, shown as glasses of 250 mlFood quality flags
When the app flags a food as high in sugar, saturated fat or salt, or scores the quality pillar in the Nutrition Report, it compares your logged food against public dietary limits.
Sugar: WHO recommends free sugars stay under 10% of total energy, and suggests under 5% for further benefit. Saturated fat: the Dietary Guidelines for Americans set a limit of less than 10% of daily calories. Sodium: the FDA Daily Value is less than 2,300 mg a day, and 1 g of salt is about 393 mg of sodium.
These are population guidance for healthy adults, not personal limits set for you.
Sources (3)
- World Health Organization. Guideline: Sugars intake for adults and children. Geneva, 2015.
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025 — saturated fat below 10% of calories.
- U.S. Food and Drug Administration. Sodium in Your Diet — Daily Value of 2,300 mg.
Vitamins and supplements
For a vitamin or mineral, the suggested amount is the gap between the recommended intake for your sex and age (the same US Dietary Reference Intakes as the nutrient panel) and what your food gave you on average over the last 7 full days. Food counts only when at least 3 days are logged and at least 70% of the calories come from foods with vitamin and mineral data; otherwise the app shows the whole recommended intake.
The suggestion never goes above the tolerable upper intake level minus your food: vitamin D 100 µg = 4,000 IU (EFSA and US), vitamin C 2,000 mg (US), zinc 25 mg (EFSA), iron 45 mg (US), calcium 2,500 mg (EFSA and US; the US sets 2,000 mg over 50). Magnesium from supplements is capped at 250 mg a day (EFSA). 1 µg of vitamin D = 40 IU.
Creatine: studies use 3–5 g a day (International Society of Sports Nutrition); the app suggests 3 g under 60 kg of body weight and 5 g otherwise. Omega-3: EFSA's adequate intake is 250 mg of EPA+DHA a day, and up to 5 g a day from supplements raises no safety concern.
These are reference values for healthy adults, not a prescription. If you have a health condition, take medication, or are pregnant or breastfeeding, ask a doctor or pharmacist before you take a supplement.
suggestion = min(reference intake − food average, upper limit − food average); magnesium from supplements ≤ 250 mgSources (5)
- National Institutes of Health, Office of Dietary Supplements. Dietary Supplement Fact Sheets — Recommended Dietary Allowances and Tolerable Upper Intake Levels.
- European Food Safety Authority. Dietary Reference Values and Tolerable Upper Intake Levels for vitamins and minerals.
- Kreider RB, Kalman DS, Antonio J, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. J Int Soc Sports Nutr. 2017;14:18.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol. EFSA Journal. 2010;8(3):1461.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the Tolerable Upper Intake Level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). EFSA Journal. 2012;10(7):2815.