Overview
This calculator estimates your daily calorie needs with the Mifflin-St Jeor equation, the equation clinical reviews generally rate as the most accurate predictive BMR formula. You enter sex, age, height in centimetres, weight in kilograms and an activity level, and the page returns BMR, TDEE, and eat-below or eat-above targets rounded to whole kilocalories. Everything runs locally in the browser.
How It Works
Pick your sex, then type your age (the input accepts 10 to 100), height in centimetres and weight in kilograms. Choose an activity level from five presets: Sedentary (1.2), Light (1.375), Moderate (1.55), Active (1.725) or Athlete (1.9). BMR and TDEE update instantly as you edit any field, no submit button needed. Below the two headline numbers you get three targets: maintenance, minus 500 kcal for a loss of roughly 0.5 kg per week, and plus 500 kcal for a comparable gain. Copying a number is as simple as reading it - there is no account, no tracking and no network request.
Step-by-Step Usage Guide
- Select your sex, the first field in the grid.
- Enter age, height in centimetres and weight in kilograms.
- Choose the activity level that matches a typical week, not your best week.
- Read BMR, TDEE and the three calorie targets, which recalculate on every keystroke.
Technical Specifications & Standards
The engine implements the Mifflin-St Jeor equation published in 1990: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years), plus 5 for men or minus 161 for women. BMR is the energy your body uses at complete rest. TDEE (total daily energy expenditure) multiplies that baseline by an activity factor - the five values shown are the standard 1.2 to 1.9 scale used in nutrition practice. The equation predicts measured resting energy expenditure within about 10 percent for most non-obese adults, which means a real metabolic lab test can reasonably disagree with this page by a couple hundred kilocalories. The loss and gain targets apply a flat 500 kcal/day offset, the conventional figure behind the rough rule that a 500 kcal daily deficit moves body weight by about half a kilogram per week. That offset ignores metabolic adaptation, body composition and individual variance. Inputs are metric only; there is no lb/in switch, so imperial users need to convert first.
Targeted Use Cases
- Setting a calorie budget before starting a weight-loss or muscle-gain phase.
- Comparing how much more a physically active job or training block raises TDEE.
- Checking whether a diet plan's calorie target is far above or below your estimated needs.
- A coach estimating starting calories for a client before adjusting from real-world results.
Notes & Gotchas
- Use your current weight, not your goal weight, or the estimate compounds the error.
- Pick the activity level below what you hope to do; most people overestimate.
- Treat the minus-500 target as a starting point and adjust after two weeks of real data.
- Recalculate after every 3 to 5 kilograms of weight change.
Frequently Asked Questions
How accurate is the Mifflin-St Jeor equation?
Validation studies report it predicts measured resting metabolic rate within roughly 10 percent for most adults, and it outperforms the older Harris-Benedict equation. Individual variation from body composition, genetics and health conditions still applies.
Is this medical advice?
No. This is a statistical estimate for healthy adults. If you have a medical condition, a history of disordered eating, or you are pregnant, discuss calorie targets with a doctor or registered dietitian instead of a calculator.
Why do I have to enter centimetres and kilograms?
The implementation is metric-only by design. One inch is 2.54 cm and one pound is 0.4536 kg, so convert those two numbers and the output matches any metric calculation.
Why exactly 500 calories for the loss target?
A 500 kcal daily deficit equals about 3,500 kcal per week, the traditional figure behind half a kilogram of fat loss per week. Real adaptation varies, so treat it as an opening estimate rather than a guarantee.