This calorie calculator estimates what you burn at rest with the Mifflin-St Jeor equation, multiplies it by an activity factor to get your total daily energy expenditure, and returns three numbers: what to eat to lose fat, what to eat to hold your weight, and what to eat to build muscle.
Calories are the first lever in any basic healthy eating plan, and the most common reason a plan stalls is that nobody ever put a number on it. Fill in the fields below to get yours, then read on to understand what the calculator is actually doing and how to correct it against real-world results. This guidance is general education, not personalized medical advice.
Protein target: 128–176 g per day, spread across your meals.
These are estimates, not prescriptions. Real energy needs vary by roughly 10 percent either way. Eat at the number for two to three weeks, track your weight, and adjust from what actually happens on the scale.
How the Calculation Works
The calculator runs in two steps. First it estimates your basal metabolic rate (BMR) — the energy your body spends staying alive with zero activity on top. Then it scales that up to your total daily energy expenditure (TDEE), which is what you actually eat against.
Step 1: The Mifflin-St Jeor Equation
Published by Mifflin, St Jeor and colleagues (1990, American Journal of Clinical Nutrition), this is the formula behind the numbers above:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
A systematic review by Frankenfield, Roth-Yousey and Compher (2005, Journal of the American Dietetic Association) compared the common predictive equations against measured resting metabolic rate and found Mifflin-St Jeor the most reliable in healthy non-obese adults, which is why it is used here instead of the older Harris-Benedict formula.
Step 2: The Activity Multiplier
BMR is then multiplied by a factor that accounts for everything you do on top of lying still:
- 1.2 — Sedentary: desk job, little or no exercise.
- 1.375 — Light: training one to three days a week.
- 1.55 — Moderate: training three to five days a week.
- 1.725 — High: training six to seven days a week.
- 1.9 — Athlete: hard training plus a physically demanding job.
This is the step most people get wrong, and they get it wrong in the same direction: they pick the level that matches their most ambitious week rather than their average one. Count your job, not just your training. A warehouse worker who never trains often burns more than an office worker who lifts four times a week.
What to Do With Your Number
If You Want to Lose Fat
Take the deficit number. A 500-calorie daily deficit works out to roughly one pound (about 0.45 kg) of fat a week — slow enough to hold onto muscle, fast enough to see the trend within a fortnight. Bigger deficits do not reliably produce better body composition, they just make the diet harder to keep and cost you more lean mass on the way down.
If You Want to Build Muscle
Take the surplus number. 200 to 300 calories above maintenance supplies the raw material for new tissue without much spillover into fat. Muscle is built slowly no matter how much you eat, so a larger surplus mostly buys you a longer cut later.
If You Want to Hold Steady
Eat at maintenance. This is the right choice more often than people think: after a long diet, during a stressful period, or any time your priority is training performance rather than the scale. See the maintenance phase guide for how to run one deliberately.
Then Set Your Protein
The calculator also returns a protein range of 1.6 to 2.2 grams per kilogram of bodyweight. Protein is the most satiating macronutrient (Halton & Hu, 2004) and the one that protects lean mass in a deficit, so it is the first macro to lock in. Once protein and calories are set, carbs and fats fill the remainder — the detail is in the macro tracking guide.
Why the Number Will Drift
A calorie target is not a permanent setting. Two things move it over time.
You get smaller. A lighter body costs less to run. Lose 10 kg and your maintenance drops by roughly 100 to 150 calories a day purely from the mass you are no longer carrying around, which is why a deficit that worked in month one can look like maintenance by month four.
Your body adapts. Extended dieting produces a measurable reduction in energy expenditure beyond what the weight loss alone predicts, and spontaneous movement tends to fall as well: less fidgeting, fewer stairs, slower walking. None of it is a metabolism that is "broken," but it does mean the arithmetic shifts under you.
The fix is simple. Re-run this calculator after every 5 kg of change, or whenever the scale has been flat for three straight weeks while you have been consistent. Then keep going.
The Lock In Protocol
A calculator gives you a starting line, not a verdict. Every equation in existence is a population average applied to one person, so treat the number as your opening bid: eat at it for two to three weeks, weigh yourself under the same conditions a few times a week, and let the trend line correct the estimate. If your weight moves the way you wanted, the number was right. If it does not, adjust by 100 to 200 calories and run it again. The scale is the real calculator. This one just saves you the first month of guessing.
Key Takeaways
- BMR is not your calorie target. It is what you burn at complete rest. Your target is BMR multiplied by an activity factor.
- Mifflin-St Jeor is the equation to use. It outperforms the older Harris-Benedict formula in validation studies on non-obese adults.
- A deficit of 500 calories is the default. That is roughly one pound of fat a week, slow enough to protect muscle.
- Surpluses should be small. 200-300 calories above maintenance builds muscle without much fat gain.
- Recalculate after big weight changes. A body 10 kg lighter burns meaningfully fewer calories.
Frequently Asked Questions
How accurate is this calorie calculator?
Predictive equations land within about 10 percent of measured resting energy expenditure for most people, which means your real maintenance could be 200-300 calories above or below the estimate. That is why the number is a starting point you validate against the scale over two to three weeks, not a fixed prescription.
What is the difference between BMR and TDEE?
BMR is the energy your body burns doing nothing at all: breathing, circulating blood, keeping your organs running. TDEE is BMR plus everything else you do, including movement, exercise, and digesting food. TDEE is the number you actually eat against.
Which activity level should I pick?
Pick based on your whole week, not your best week, and count your job as well as your training. Most people who train three or four times a week but sit at a desk should choose moderate. When in doubt, choose the lower option: it is easier to add calories than to explain why the scale did not move.
Why does the calculator warn me below 1,200 calories?
Very low intakes make it hard to hit protein and micronutrient needs and are strongly linked to muscle loss. If your deficit target lands under 1,200 calories, eat at maintenance or use a smaller 300-calorie deficit and speak to a doctor or dietitian before going lower.
Do I need to eat exactly this number every day?
No. Weekly totals drive results, not daily ones. Landing within about 100 calories of the target most days, and averaging out across the week, produces the same outcome as hitting it exactly.
References
- Mifflin, M. D., St Jeor, S. T., Hill, L. A., et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2), 241–247.
- Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 105(5), 775–789.
- Halton, T. L., & Hu, F. B. (2004). The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. Journal of the American College of Nutrition, 23(5), 373–385.
- Caloric requirements and energy balance (PMC)
- Caloric deficit for weight loss (NCBI)
- Caloric surplus for muscle gain (PMC)
- Protein intake preserves lean body mass (PubMed)
- Adaptive thermogenesis and metabolic adaptation to weight loss (PMC)
- Calorie deficit explained (Healthline)