A calculator can give you a starting point. Understanding its assumptions helps you use that starting point well.

What this calculator does

Daily energy is approximated as resting energy multiplied by an activity factor. The factors are 1.2, 1.375, 1.55, 1.725 and 1.9. They are rough planning categories, not measured energy expenditure. Work, movement, training, body composition and individual variation all matter.

The equations, in the open

Weight (W) is in kilograms, height (H) in centimetres, age (A) in years, and fat-free mass (FFM) in kilograms.

Mifflin–St JeorMale: 10W + 6.25H − 5A + 5
Female: 10W + 6.25H − 5A − 161Revised Harris–BenedictMale: 88.362 + 13.397W + 4.799H − 5.677A
Female: 447.593 + 9.247W + 3.098H − 4.330AKatch–McArdle370 + 21.6 × FFMCunningham (resting metabolic rate)500 + 22 × FFM

BMR and RMR are measured under different conditions. They are grouped here for comparison as resting-energy estimates; the labels do not make them identical. In automatic mode we use Mifflin–St Jeor unless body fat is supplied, when we use Katch–McArdle. You can override this selection. A body-fat measurement error can reduce usefulness.

Goals and macro planning

Weight-loss planning uses a selectable 10%, 15% or 20% deficit. Weight-gain planning uses a 10% surplus. Maintenance uses the estimate unchanged. Protein uses 1.6 g/kg for maintenance and 1.8 g/kg for loss or gain; fat uses 28% of target calories and carbohydrates use the remaining calories (4 kcal/g protein and carbohydrate, 9 kcal/g fat). Rounded grams may not add up to the exact calorie target. These are adjustable planning conventions, not an individualized prescription.

Caution rules and scope

The tool is for generally healthy adults aged 18–100. It does not support pregnancy, breastfeeding, children, or medical nutrition therapy. Goals below 1,200 kcal for the female equation or 1,500 kcal for the male equation trigger a caution and hide the macro prescription. These thresholds are product guardrails, not scientifically universal minimum needs. Higher intakes can still be insufficient. Weight-loss output is withheld when BMI is below 18.5.

What the journal can tell you

After 21 consecutive daily records with calorie intake, we compare the first and last 7-day average weights. Average recorded intake minus the weight-change energy equivalent per day gives a rough observed-energy estimate. We use 7,700 kcal/kg only as a simplified conversion, not a physiological constant. The estimate is not a prediction of a weight-loss date and does not account for metabolic adaptation, water shifts or inaccurate food logs.

Sources and further reading

Editorial transparency

This is a formula-based informational tool. No clinical review is claimed. The equations and product rules above describe the implementation; citations do not imply that an author or institution endorses this site.

Usable planning windows

The observed-energy estimate uses the latest 21 consecutive complete days, ending on your latest check-in. Earlier gaps do not invalidate that window. Its dates and any missing check-ins or intake are shown in the journal.

Macro amounts are withheld when the protein and fat estimates cannot fit the calorie target. This is a consistency check, not a substitute for individual nutrition advice.