This calculator estimates your BMR (the energy your body uses at rest) and your TDEE (what you use across a whole day), then shows a daily calorie target for your goal. It runs entirely in your browser — your age, weight, and height are never sent to us, never stored, and never attached to an email address. There is nothing to sign up for and no result is held back.
Work out your numbers
The exact formula, so you can check our work
Most calculators hand you a number and hide the maths. Here is precisely what runs, and it is the same calculation the HealthMaxxing app performs.
Step 1 — BMR, via the Mifflin-St Jeor equation (weight in kilograms, height in centimetres, age in years):
| Sex selected | BMR |
|---|---|
| Male | (10 × weight) + (6.25 × height) − (5 × age) + 5 |
| Female | (10 × weight) + (6.25 × height) − (5 × age) − 161 |
| Prefer not to say / non-binary | (10 × weight) + (6.25 × height) − (5 × age) − 78 (the midpoint of the two equations above) |
Step 2 — TDEE: BMR × an activity multiplier — sedentary 1.2, lightly active 1.375, moderately active 1.55, very active 1.725, extremely active 1.9.
Step 3 — goal: −500 kcal/day to lose, +300 kcal/day to gain, unchanged to maintain.
Step 4 — the floor. The target is never allowed below 1,500 kcal for men, 1,200 for women, and 1,300 otherwise. If the arithmetic lands lower, the floor is shown instead and the calculator says so. This is the single most important line in the whole tool: an unclamped calculator will happily print a number a person should not eat.
What this cannot know
- It is an estimate, not a measurement. Mifflin-St Jeor is a population equation; individual metabolic rate varies around it. Only indirect calorimetry actually measures your rate.
- Activity multipliers are coarse. Two people picking “moderately active” can differ by hundreds of calories a day.
- It does not account for body composition, medication, pregnancy or breastfeeding, thyroid or metabolic conditions, or a history of disordered eating.
- Weight-change targets are shown for adults only. Under 18, the calculator shows BMR and TDEE but no weight-change target — growth-stage energy needs are not something a web form should be prescribing.
This is general wellness information, not medical advice, and no doctor–patient relationship is formed by using it. If you are managing a health condition, are pregnant or breastfeeding, are under 18, or have any history of disordered eating, decide calorie targets with a clinician or registered dietitian rather than a calculator. If tracking calories increases anxiety, guilt, or compulsion, that is a reason to stop.
Why nothing you type reaches us
Every number above is computed by JavaScript in your own browser. Nothing is transmitted, nothing is written to storage, and no result is tied to an email address — because health inputs attached to an identity are exactly the kind of data that should not accumulate on a marketing site. If you later join the waitlist, that stores your email address and nothing else.
Where this goes next
A calorie target is one number on one day. The more useful question is which of your habits actually track with how you feel — which is what HealthMaxxing is built to answer, using this same calculation for its calorie plan. It is coming soon to iPhone and Android, and the core tracking is free at launch.
- Mifflin MD, St Jeor ST, et al. “A new predictive equation for resting energy expenditure in healthy individuals.” — American Journal of Clinical Nutrition, 1990. The equation used in Step 1.