Calorie Calculator
Calculate your BMR and TDEE using the Mifflin-St Jeor equation. Free daily calorie needs estimator — no account needed, works instantly in your browser.
Calorie Calculator
Mifflin-St Jeor Equation
Your Data
What Is a Calorie Calculator?
A calorie calculator estimates how many calories your body needs each day based on your age, weight, height, sex, and activity level. This tool uses the Mifflin-St Jeor equation — validated by the Academy of Nutrition and Dietetics as the most clinically accurate non-invasive method for calculating BMR in modern adults — to produce your Basal Metabolic Rate and Total Daily Energy Expenditure.
These two numbers give you the foundation for any evidence-based dietary plan: whether you want to lose weight, maintain your current physique, or support muscle growth. The results are estimates based on population averages and are not a substitute for personalized advice from a registered dietitian or physician.
How to Use the Calorie Calculator
Enter your physical stats. Input your age, biological sex, height, and current weight. Use the unit toggle to switch between metric and imperial.
Select your activity level. Choose the level that best describes your average week — from sedentary (desk job, little exercise) to very active (physical labor or twice-daily training).
Read your BMR and TDEE. The calculator outputs your Basal Metabolic Rate (resting needs) and Total Daily Energy Expenditure (actual daily burn).
Set your calorie target. Subtract 300–500 from TDEE for weight loss, eat at TDEE for maintenance, or add 250–500 for muscle gain. Recalculate every 10–15 lbs of change.
Who Is This For?
- →People planning a calorie deficit for weight management — getting a reliable baseline number before adjusting their diet rather than guessing.
- →Athletes calculating maintenance calories for performance — understanding TDEE at different training volumes to fuel workouts without surplus fat gain.
- →Anyone who wants to understand their baseline energy needs — before starting a new diet, training program, or nutritional tracking habit.
Key Benefits
- ✓Private — your personal health data runs entirely in your browser and is never sent to any server.
- ✓Completely free — no subscription, no paywall, no account required.
- ✓No account required — open the page and calculate immediately.
- ✓Mifflin-St Jeor accuracy — uses the formula validated by the Academy of Nutrition and Dietetics, not the outdated Harris-Benedict equation that overestimates needs.
Understanding BMR vs. TDEE
Basal Metabolic Rate (BMR)
Your BMR is the minimum amount of energy your body needs to keep you alive at complete rest — fueling brain function, heartbeat, breathing, and cellular regeneration. For most adults, BMR accounts for roughly 60–70% of total daily energy burned.
Total Daily Energy Expenditure (TDEE)
TDEE takes your BMR and multiplies it by an activity factor to account for physical movement. It encompasses your resting burn, intentional exercise (EAT), unconscious daily movement (NEAT), and the energy cost of digesting food (TEF). TDEE is the number you actually use for dietary planning — not BMR.
Creating a Caloric Deficit
To lose weight, you must consume fewer calories than your TDEE. One pound of body fat contains approximately 3,500 calories, so a sustained deficit of 500 calories per day yields roughly 1 pound of fat loss per week.
Avoid extreme restriction — dropping below 1,200 calories (women) or 1,500 calories (men) without medical supervision risks muscle loss, hormonal disruption, and metabolic adaptation.
Caloric Surpluses (Building Muscle)
Building muscle tissue requires a sustained caloric surplus. For a "clean bulk" — gaining muscle without excess fat — aim for 250 to 500 calories above TDEE daily.
This ensures the body has ample protein and glycogen available to synthesize new muscle fibers following resistance training, without accumulating significant body fat.
The Science: The Mifflin-St Jeor Equation
Historically, dietitians relied on the Harris-Benedict equation (created in 1919) to calculate BMR. As human lifestyles and average body compositions evolved over the 20th century, that formula was shown to consistently overestimate daily caloric needs.
In 1990, the Mifflin-St Jeor equation was published and has since been validated by the Academy of Nutrition and Dietetics as the most clinically accurate non-invasive method for estimating BMR in modern adults. This tool uses that exact formula.
Frequently Asked Questions
How are daily calorie needs calculated? ▼
The Mifflin-St Jeor equation calculates your Basal Metabolic Rate — the calories your body needs at complete rest — then multiplies by an activity factor ranging from 1.2 for sedentary to 1.9 for very active. This result is your TDEE, Total Daily Energy Expenditure. This tool performs that calculation automatically based on your age, weight, height, sex, and activity level.
Is this tool free to use? ▼
Yes, completely free. No subscription, no paywall, and no account required. The calculator runs entirely in your browser — your personal data is never sent to any server.
How many calories do I need to lose weight? ▼
A deficit of 500 calories per day below your TDEE is a general guideline for losing approximately 1 pound per week, since one pound of body fat contains roughly 3,500 calories. However, eating below 1,200 calories per day (for women) or 1,500 calories per day (for men) is not recommended without medical supervision, as this can trigger muscle loss and metabolic adaptation.
What is the difference between BMR and TDEE? ▼
BMR is your baseline metabolic rate at complete rest — the calories just to keep your organs functioning. TDEE is BMR multiplied by your activity level and represents your actual daily calorie expenditure including movement, exercise, and the energy cost of digesting food. TDEE is the number you use for dietary planning.
Do macronutrients matter if my calories are equal? ▼
For strict weight change, total calorie balance is the primary driver. However, macronutrients — protein, fats, and carbohydrates — determine body composition. Without adequate protein in a calorie deficit, your body will burn muscle tissue alongside fat. Most nutrition professionals recommend 0.7–1g of protein per pound of body weight when in a deficit.
Why is my weight loss stalling even in a calorie deficit? ▼
As you lose body mass, your BMR naturally decreases because a lighter body requires fewer calories to maintain. A 500-calorie deficit at 250 lbs is different from a 500-calorie deficit at 200 lbs. Recalculate your TDEE every 10–15 lbs of weight loss to re-establish your new metabolic baseline and adjust your target accordingly.
The tools and calculators provided on The Simple Toolbox are intended for educational and informational purposes only. They do not constitute financial, legal, tax, or professional advice. While we strive to keep calculations accurate, numbers are based on user inputs and standard assumptions that may not apply to your specific situation. Always consult with a certified professional (such as a CPA, financial advisor, or attorney) before making significant financial or business decisions.
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