Most people trying to change their weight are working with a number they picked up somewhere — "eat 1,500 calories" — without knowing where it came from or whether it applies to them. This calculator gives you a number that's grounded in your actual body: your weight, height, age, sex, and how active you genuinely are, not how active you'd like to be.
It does this in four steps: estimate your resting calorie burn (BMR), scale it by your activity level (TDEE), shift it up or down based on your goal, then divide the result into protein, carbohydrate, and fat targets.
BMR (basal metabolic rate) is the number of calories your body would burn over 24 hours if you lay completely still. It keeps your heart beating, your liver filtering, your kidneys running, your brain lit up. It's largely determined by how much tissue you have that needs maintaining — which is why heavier, taller, younger, and more muscular people generally have higher BMRs.
The calculator uses the Mifflin-St Jeor equation, which most registered dietitians and sports-nutrition bodies recommend for healthy adults:
The older Harris-Benedict equation (still shown on many calculators) tends to overestimate BMR by 5–8% compared to measured values in metabolic studies. Mifflin-St Jeor tracks more closely, which is why it replaced it.
TDEE (total daily energy expenditure) is your BMR multiplied by an activity factor. The factors the calculator uses:
The consistent finding in nutrition research is that people overestimate their activity level by one category. A few gym sessions a week does not make you "very active" if the other 23 hours of your day are sedentary. When in doubt, pick one level lower and adjust after 2–4 weeks based on what the scale actually does.
The tool shifts your TDEE up or down based on your goal:
The 3,500 kcal-per-pound rule is an approximation that works reasonably well for fat tissue but breaks down over longer periods due to metabolic adaptation — your body adjusts its burn rate in response to sustained deficits. The target is floored at 1,200 kcal/day; going below that without medical supervision makes it very hard to hit micronutrient targets.
Once you have a calorie target, the tool divides it into three macronutrients:
Every input — age, sex, height, weight, activity level, goal — is encoded into the
URL hash (the fragment after #). Copy the URL and you can bookmark it,
reopen it in three months, or send it to a trainer. The hash never leaves your device
unless you copy and share the link yourself; nothing is stored on any server.
Population-average formulas produce population-average results. They're accurate enough to give you a starting point but won't account for medical conditions, hormonal factors, unusually high or low lean mass, or the specific way your body responds to a deficit. Treat the output as a starting hypothesis, track what happens over 2–4 weeks, and adjust from there.
If you have a medical condition, are pregnant or breastfeeding, or are recovering from an eating disorder, consult a registered dietitian before changing your intake.