Calculator › How it works
How the calculator works
Transparent maths, so you know exactly where your numbers come from.
1. Basal Metabolic Rate (BMR)
We use the Mifflin-St Jeor equation, widely regarded as one of the most accurate for healthy adults:
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 (men)BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161 (women)
2. Total Daily Energy Expenditure (TDEE)
BMR is multiplied by an activity factor:
| Level | Factor | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise 1–3 days a week |
| Moderately active | 1.55 | Exercise 3–5 days a week |
| Very active | 1.725 | Hard exercise 6–7 days a week |
| Extra active | 1.9 | Physical job plus daily training |
3. The deficit
One kilogram of body fat holds roughly 7,700 Cal (32,217 kJ). Daily deficit = pace (kg/week) × 7,700 ÷ 7.
4. Safety limits
Your target is never set below your BMR, nor below 1,200 Cal for women or 1,500 Cal for men. If your chosen pace would breach this, we raise the target and tell you.
5. Kilojoules
1 Cal (kcal) = 4.184 kJ. Australian packaging uses kJ, so results show in kJ by default.
Limitations
These are estimates. Metabolism adapts as you lose weight, and individuals vary. Not for under-18s, pregnancy, breastfeeding or people with medical conditions. Talk to your GP or an Accredited Practising Dietitian.