Macro, Protein and Weight-Loss Calculator
Estimate adult resting energy expenditure with the Mifflin–St Jeor equation, apply an activity factor and translate a user-chosen calorie adjustment into protein, fat and carbohydrate targets.
Enter an adult energy scenario
Use the macro split as a monitored starting scenario, not a medical or sports-performance prescription.
From resting energy to a daily scenario
The Mifflin–St Jeor equation estimates resting energy expenditure from body mass, height, age and one of two sex-specific constants. It predicts energy used at rest under study conditions; it does not directly measure metabolism. The script then multiplies that estimate by an activity factor to create a maintenance scenario and adds the calorie adjustment entered by the user.
Every stage adds uncertainty. Body composition, spontaneous movement, training load, climate, illness, sleep and food intake can move actual expenditure away from the prediction. Treat the result as a starting hypothesis to be calibrated against several weeks of consistent body-mass, intake and performance observations, not as a metabolic fact.
Selecting the equation constant
The original equation provides a +5 constant for males and a -161 constant for females. The selector represents that published mathematical choice; it is not a statement about identity. People who are intersex, transgender, using gender-affirming hormones or unsure which equation is clinically suitable should discuss the estimate with an appropriately qualified professional.
The difference between the two constants is 166 kcal per day while the remaining weight, height and age terms stay the same. Run both only to see formula sensitivity, not to pick whichever supports a preferred intake. Measured indirect calorimetry, where indicated and properly performed, provides different evidence from either prediction.
Activity multipliers are broad categories
An activity factor attempts to cover planned exercise, occupational movement, daily steps, posture and the thermic effect of food in one multiplier. Labels such as light or moderate are therefore imprecise. Two people doing the same gym sessions can have very different total movement because one has a desk job and the other performs manual work.
Choose a conservative starting factor and compare predicted maintenance with observed trend. If body mass is stable over a sufficiently long, consistently tracked period, average intake offers useful evidence about maintenance. One unusually active week or a rapid water-weight change is not enough to recalibrate the factor.
Calorie deficit and weight change
A negative adjustment creates an energy-intake scenario below predicted maintenance. It does not promise a fixed weekly loss because energy expenditure adapts, tracking is imperfect and body mass includes water, glycogen, gut contents, fat and lean tissue. The often-quoted conversion between calories and a kilogram of fat is too simple for precise forecasting over time.
Use modest adjustments and monitor wellbeing, hunger, training, sleep and trend. An aggressive deficit can impair performance, increase nutrient shortfalls and be inappropriate at a low body mass or during illness. Children and adolescents should not use this adult interface. Clinical obesity care and unintended weight loss require professional assessment.
Protein target
Protein grams are body mass multiplied by the entered grams-per-kilogram target. The default 1.6 g/kg is a planning value often used around resistance training and energy restriction, not a universal requirement. Needs depend on total energy, training, age, dietary pattern, health and the meaning of body mass in a specific clinical context.
More protein is not automatically better. Extremely high targets can displace fibre-rich carbohydrate, fats and micronutrient sources. People with kidney disease or other conditions should not adopt a high-protein target from an online estimate. Distribute intake across foods and meals in a pattern that is affordable, culturally suitable and clinically appropriate.
Fat and carbohydrate allocation
The fat field allocates a percentage of target calories, using nine kcal per gram. Protein is assigned four kcal per gram, and carbohydrate receives the remaining calories at four kcal per gram. If protein and fat consume more calories than the target, the calculator stops rather than displaying negative carbohydrate.
Macro percentages do not measure diet quality. The sources of carbohydrate and fat, fibre, micronutrients, food processing, allergies and total dietary pattern matter. A calculated gram target should not push out fruit, vegetables, legumes or other foods recommended for the individual. Alcohol also supplies energy but is not allocated as a macro target here.
Tracking without false precision
Food labels and restaurant portions carry uncertainty, and home measurements can vary. A target of 2,071 kcal should usually be treated as an approximate range rather than a requirement to hit one exact calorie. Consistent methods are more informative than switching between scales, cooked and raw database entries or portion assumptions from day to day.
Review weekly averages and longer-term trends. Rapid daily body-mass movements commonly reflect fluid rather than tissue change. If weight trend diverges from the plan, adjust gradually and observe again. Do not continually cut intake in response to a single high weigh-in.
When the estimate is unsuitable
Pregnancy and breastfeeding change energy and nutrient needs. Eating-disorder history, diabetes medication, kidney or liver disease, major gastrointestinal disease, recent surgery and unexplained weight change require personalised care. Athletes with very high training loads also face performance and low-energy-availability risks that a general activity factor cannot manage.
Stop using the output as a target if it promotes dizziness, fainting, persistent fatigue, menstrual disturbance, loss of training capacity or obsessive restriction. Seek a registered dietitian or relevant clinician. The calculator cannot assess body image, nutrient deficiency, medical stability or whether weight loss is indicated.
A four-week calibration process
Record the chosen formula inputs, average intake, morning body mass under consistent conditions and major activity changes. Compare a rolling trend after several weeks, allowing for menstrual-cycle and sodium-related fluid changes where relevant. If trend is stable, the maintenance estimate may be close enough for planning; if not, adjust by a modest amount.
Recalculate after meaningful body-mass change because the equation uses weight. Keep performance and health outcomes alongside the scale. A plan that moves weight but harms strength, concentration or adherence is not successful. Use professional advice when the acceptable trade-offs are unclear.
Questions that affect this result
Is the calorie result my measured metabolism?
No. It is a prediction from an equation and activity multiplier. Actual expenditure can differ materially.
Which equation constant should a transgender person choose?
The published equation has sex-specific constants but does not address every clinical situation. A qualified professional can help interpret or replace the estimate.
Does a 500 kcal deficit guarantee a fixed weekly loss?
No. Weight dynamics, water changes, adaptation and tracking error prevent a guaranteed linear result.
Can I set carbohydrate to zero?
The page calculates carbohydrate as the remainder after protein and fat. A restrictive clinical diet should be supervised rather than designed from this general interface.
Who should avoid using this as a nutrition target?
Minors, pregnant or breastfeeding people, anyone with an eating disorder or major medical condition, and people with unexplained weight change should seek individual care.