How the calculator works
Every number on this site comes from the steps below, in this order. If you want to check a result by hand, this page has everything you need.
1. Resting energy (BMR)
Weight in kilograms, height in centimetres, age in years.
| Equation | Men | Women | Used |
|---|---|---|---|
| Mifflin-St Jeor (1990) | 10W + 6.25H − 5A + 5 | 10W + 6.25H − 5A − 161 | Always |
| Harris-Benedict, revised by Roza & Shizgal (1984) | 88.362 + 13.397W + 4.799H − 5.677A | 447.593 + 9.247W + 3.098H − 4.330A | Always |
| Katch-McArdle | 370 + 21.6 × lean mass | With body fat % | |
| Cunningham (1980) | 500 + 22 × lean mass | With body fat % | |
BMR is the plain average of the equations in use. "Prefer not to say" averages the male and female versions. The lean-mass equations are used only with a body-fat figure you enter: an estimate from BMI is too rough to feed into them, so it is shown for information but not used.
2. A MET scaled to you
The 2024 Adult Compendium of Physical Activities gives each activity a MET value: its energy cost as a multiple of sitting at rest. We set 1 MET equal to your own BMR divided by 24, per hour, rather than the fixed 1 kcal per kg per hour, and count only the energy above rest: extra kcal = (MET − 1) × BMR/24 × hours. This avoids counting your resting burn twice, since BMR already covers all 24 hours.
3. The parts of a day
| Part | How it is counted |
|---|---|
| Work | Job type MET over the shift, averaged across 7 days: desk 1.5, standing 2.0, on the move 2.5, manual 3.3. Not working: home at 1.4. |
| Steps | Stride = 41.4% of height. Distance × 0.5 kcal per kg per km, the horizontal term of the ACSM walking equation (0.1 ml O₂/kg/m at about 5 kcal per litre of oxygen). For on-the-move and manual jobs, 1,000 steps per working hour are assumed to happen at work and are not counted again. |
| Exercise | Each activity's Compendium MET, minutes per session and sessions per week, averaged over 7 days. |
| Rest of the waking day | 16 waking hours minus work, exercise and walking time, at 1.4 MET (sitting, standing and moving about at home). |
| Digestion | 10% of the total (the thermic effect of food): TDEE = (BMR + all of the above) ÷ 0.9. |
PAL (physical activity level) is TDEE ÷ BMR. The FAO/WHO/UNU 2004 report describes 1.40–1.69 as sedentary or light, 1.70–1.99 as active or moderately active and 2.00–2.40 as vigorous. Typical inputs land in those bands; we use them as a sanity check, not as an input.
4. Goal calories and macros
Goal targets are percentages of TDEE: −25%, −18% and −10% for fat loss, 0 for maintenance, +7% and +15% for gain, rounded to 10 kcal. Protein is 2.0 g per kg of body weight in a deficit and 1.8 g otherwise, capped at 2.4 g per kg of lean mass when body fat is known. Fat is 27% of calories with a floor of 0.6 g per kg. Carbohydrate is the remainder at 4 kcal per gram.
5. Body composition
BMI = kg ÷ m². Body fat from BMI uses Deurenberg et al. (1991): 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women). The body fat calculator adds the U.S. Navy circumference equations (Hodgdon & Beckett, 1984) and the Jackson-Pollock three-site skinfold equations (1978 for men, 1980 for women) with the Siri equation, %fat = 495 ÷ density − 450.
6. Strength
One-rep max is the average of Epley, weight × (1 + reps ÷ 30); Brzycki, weight × 36 ÷ (37 − reps); and Lombardi, weight × reps0.10, for sets of 1 to 12 reps.
What the method cannot do
Every step is an average fitted to groups of people. Two people with the same inputs can differ by a few hundred calories a day because of genetics, body composition the equations cannot see, and how hard they really work. That is why every tool says the same thing: use the number for two or three weeks, compare it with your weight trend, and adjust. These tools are for healthy adults and are not medical advice.