BMR Calculator
Basal Metabolic Rate (BMR)
1,618 kcal/day
Mifflin-St Jeor equation · calories burned at complete rest
Total Daily Energy Expenditure (TDEE)
2,507 kcal/day
BMR × 1.55 · Moderately Active
Daily Calorie Targets
No data stored · Results are estimates only · Not financial or medical advice
CalcTools AI's BMR Calculator uses the scientifically validated Mifflin-St Jeor equation to estimate your Basal Metabolic Rate — the number of calories your body burns at complete rest just to sustain vital functions like breathing, circulation, and cell repair.
By factoring in your activity level, the calculator also derives your Total Daily Energy Expenditure (TDEE) and maps out personalised daily calorie targets for weight loss, maintenance, or muscle gain. The integrated AI assistant then explains what these numbers mean for your specific profile and gives you actionable nutrition guidance.
How to Use the BMR Calculator
- Select your gender — biological sex affects the BMR constant in the Mifflin-St Jeor formula.
- Enter your age — metabolism slows with age; the formula accounts for this directly.
- Enter your weight — choose kg or lbs. The calculator converts automatically.
- Enter your height — choose centimetres or feet & inches.
- Choose your activity level — select the option that best describes your typical week.
- Read your results — BMR, TDEE, and a full calorie target table appear instantly.
- Click "Explain with AI" — receive a personalised narrative covering what your BMR means, how TDEE maps to your goals, and tailored nutrition tips.
- Optionally download a PDF report with all figures and the AI insight.
BMR Formula — Mifflin-St Jeor Equation
$$\text{BMR (men)} = 10w + 6.25h - 5a + 5$$
$$\text{BMR (women)} = 10w + 6.25h - 5a - 161$$
Where w = weight in kg, h = height in cm, a = age in years.
This equation was validated in 1990 and is recommended by the American Dietetic Association as the most accurate BMR formula for most adults.
TDEE — Activity Multipliers
$$\text{TDEE} = \text{BMR} \times \text{Activity Factor}$$
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Little or no exercise | × 1.20 |
| Lightly Active | Exercise 1–3 days/week | × 1.375 |
| Moderately Active | Exercise 3–5 days/week | × 1.55 |
| Very Active | Hard exercise 6–7 days/week | × 1.725 |
| Super Active | Physical job or twice-daily training | × 1.90 |
Calorie Targets Based on TDEE
| Goal | Daily Calories | Expected Rate |
|---|---|---|
| Weight Loss | TDEE − 500 kcal | ~0.5 kg / week |
| Mild Weight Loss | TDEE − 250 kcal | ~0.25 kg / week |
| Maintenance | TDEE | Weight stable |
| Mild Weight Gain | TDEE + 250 kcal | ~0.25 kg / week |
| Weight Gain | TDEE + 500 kcal | ~0.5 kg / week |
A 500 kcal daily deficit equates to roughly 3,500 kcal per week — approximately 0.45–0.5 kg of body fat. Deficits larger than 1,000 kcal/day are generally not recommended without medical supervision, as they risk muscle loss and nutritional deficiencies.
BMR vs TDEE — Key Differences
BMR is the energy your body needs at complete rest — think of it as the engine idling. It accounts for about 60–75% of total calorie expenditure for most people.
TDEE is the full picture: BMR plus all physical activity, digestion (the thermic effect of food), and non-exercise movement like walking and fidgeting. TDEE is the number you should use when planning your daily calorie intake.