A recognized formula, not a rough guess
Widely used and cited across clinical nutrition practice
BMR, maintenance, and weight-goal targets, all in one calculation
Mifflin-St Jeor formula
A well-regarded equation for estimating calorie needs, widely used and cited by dietitians and clinical nutrition guidelines.
Four targets at once
See maintenance, moderate loss, fast loss, and gain calorie targets together, so you can compare options in one view.
Private by design
Your details stay in your browser and are never sent to, logged by, or stored on a server.
Why the same weight goal needs a different number for everyone
Two people who each weigh 70kg can have meaningfully different calorie needs depending on their height, age, gender, and how active they are day to day — which is exactly why generic advice like "eat 1,500 calories to lose weight" is often wrong for a specific individual. A calorie calculator personalizes that number by starting from your body's baseline energy needs at complete rest (BMR) and then scaling it up based on how active you actually are, arriving at a maintenance figure that's a genuine starting point rather than a one-size-fits-all guess.
This is also why two popular diet plans built around the same fixed calorie number can work very differently for different people — someone with a naturally higher BMR and a more active routine may find a "1,500 calorie" plan too aggressive a deficit, while it might be roughly maintenance level for someone with a lower baseline. Personalizing the starting number is the first step toward a plan that's actually sustainable for a specific person's body and lifestyle.
How BMR and TDEE are calculated
BMR (Basal Metabolic Rate) is the number of calories your body burns just to keep basic functions running — breathing, circulation, cell repair — if you stayed in bed all day. This tool uses the Mifflin-St Jeor equation: for men, BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5; for women, BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161. This formula was developed from measured data and is considered more accurate for most modern populations than older formulas like Harris-Benedict.
TDEE (Total Daily Energy Expenditure) — your actual daily maintenance calories — takes BMR and multiplies it by an activity factor that accounts for exercise and daily movement on top of resting metabolism, ranging from 1.2 for a sedentary lifestyle to 1.9 for very intense daily training. The weight-loss and weight-gain figures shown are simply TDEE adjusted by a calorie deficit or surplus — subtracting roughly 500 calories for gradual loss, 1000 for faster loss, or adding 500 for a gradual gain, based on the widely cited approximation that roughly 7,700 calories equals about 1kg of body weight change.
It's worth noting that this 7,700-calorie rule is itself an approximation that becomes less precise over longer timeframes and larger weight changes, since the body's metabolism adapts somewhat as weight changes. It remains a reasonable planning estimate for a starting target, but actual results are best tracked and adjusted over a period of weeks rather than expected to follow the math exactly day by day.
When people use a calorie calculator
A few common situations
🥗 Starting a weight-loss plan
Get a personalized calorie target instead of relying on a generic number found online.
💪 Building muscle or gaining weight
Find a realistic calorie surplus target that supports gradual, controlled weight gain.
⚖️ Maintaining current weight
Understand roughly how many calories keep your weight stable given your activity level.
🏃 Adjusting for a change in activity
Recalculate calorie needs after starting or stopping a regular exercise routine.
📋 Working with a nutritionist
Bring a data-backed starting estimate into a conversation with a dietitian or trainer.
🎓 Understanding metabolism basics
See how BMR and activity level combine into a real daily calorie number.
🩺 Ahead of a health check-in
Bring a general baseline figure to a routine health or nutrition consultation for reference and discussion.
📊 Tracking alongside a food diary
Compare a food log's daily total against an estimated target range for context, rather than a strict number to hit exactly every day.
What each activity level generally means
| Activity level | General description |
|---|---|
| Sedentary | Little to no regular exercise, mostly desk-based day |
| Lightly active | Light exercise or walking 1-3 days a week |
| Moderately active | Moderate exercise 3-5 days a week |
| Very active | Hard exercise 6-7 days a week |
| Extremely active | Very hard daily exercise or a physically demanding job |
Picking the level that matches your typical week, rather than an especially active or especially rest-heavy single day, gives the most representative TDEE estimate — and re-checking this level every time your routine changes meaningfully keeps the estimate reasonably accurate over time.
Why this is an estimate, not an exact number
The Mifflin-St Jeor formula is one of the more accurate published equations for estimating BMR, but it's still a population-level estimate based on age, sex, height, and weight — it can't account for individual variation in muscle mass, genetics, hormone levels, or metabolic health, all of which affect actual calorie burn to some degree. Two people with identical stats on this calculator can have genuinely different real-world metabolic rates, sometimes by a meaningful margin. The activity multiplier used to estimate TDEE is similarly a rough category rather than a precise measurement of actual daily movement.
For this reason, the numbers here are best used as a starting point to adjust from based on real-world results — if weight isn't changing as expected after a few consistent weeks at a given calorie target, that's useful information to recalibrate the target, rather than a sign the formula failed. Anyone with a specific medical condition, a history of disordered eating, or a significant weight goal should work with a doctor or registered dietitian rather than relying on a calculator alone, since a general-purpose formula can't account for individual medical circumstances the way a professional assessment can.
Using the estimate alongside real-world tracking
Because this calculator's output is a starting estimate rather than a measured value, the most reliable way to use it is as a baseline to check against actual results over time. If weight tracked over a few consistent weeks is moving faster or slower than the formula's rough deficit-to-weight-change guideline would suggest, that's useful real-world data pointing to where your actual metabolism sits relative to the estimate — adjusting the target based on that feedback tends to work better than assuming the initial number is exactly correct, since it accounts for individual variation the formula itself can't capture.
Weight itself also fluctuates day to day due to water retention, digestion, and other short-term factors unrelated to actual fat or muscle change, so looking at a weekly or monthly trend rather than a single day's number gives a clearer picture of whether a calorie target is having the intended effect. This is standard practice recommended by most nutrition professionals when working with any calorie estimate, not a limitation specific to this calculator, and it applies whether the goal is weight loss, maintenance, or gain.
Quick recap
Daily calorie needs come from two numbers combined — BMR (resting energy burn, calculated from age, sex, height, and weight) and an activity multiplier that scales it up for how much you move. The resulting maintenance, loss, and gain targets are genuinely personalized starting estimates, not exact measurements, and are best treated as a baseline to track and adjust from based on real results over a few weeks rather than a fixed number to follow exactly.
Calorie needs come from two layers — BMR, your body's baseline resting energy use, and an activity multiplier on top of it — combined using the well-regarded Mifflin-St Jeor formula. The maintenance, loss, and gain figures shown are a solid personalized starting point, not a guarantee, since real-world results also depend on factors like sleep, stress, and individual metabolic variation; treat the numbers as a baseline to adjust from based on how your actual weight trends over a few weeks.
📖 How to use the calorie calculator
Frequently asked questions
How accurate is this calorie calculator?
It uses the Mifflin-St Jeor formula, which is widely regarded as one of the most accurate equations for estimating calorie needs in most adults, though individual metabolism can still vary from the formula's estimate.
How many calories should I eat to lose weight?
A deficit of about 500 calories below maintenance typically leads to roughly 0.5 kg of weight loss per week, according to the widely cited calorie-to-weight approximation. Always consult a doctor before starting any diet plan, especially for larger deficits or specific health conditions.
What is BMR and how is it different from TDEE?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest just to maintain basic functions. TDEE (Total Daily Energy Expenditure) adds your activity level on top of BMR to estimate your total daily calorie burn including movement and exercise.
Should I use the same activity level even on rest days?
The activity level here reflects your typical weekly average, so a single rest day doesn't require recalculating — pick the level that best describes your usual week rather than any single day.
Is this tool free?
Yes, completely free with no signup required.
Why did my calorie needs change after I changed my activity level?
Activity level is one of the two main inputs (alongside BMR) in the TDEE calculation, so any change to it directly shifts the estimated daily calorie need — a more active lifestyle increases the estimate, a less active one lowers it.
Is this calculator accurate for athletes or very muscular individuals?
The formula is less precise for people with unusually high muscle mass, since it's based on general population data using age, sex, height, and weight rather than actual measured body composition.
How often should I recalculate my calorie needs?
Recalculating after a meaningful weight change (a few kilograms), a significant activity level change, or every few months during an active weight-loss or gain phase keeps the estimate reasonably current.
Is my health data stored anywhere?
No, all calculations run entirely in your browser and your age, weight, height, and activity level are never sent to or stored on a server.
Why does BMR use different formulas for men and women?
The Mifflin-St Jeor equation includes a sex-specific adjustment term because average body composition differs between men and women at the same age, height, and weight, which affects resting metabolic rate.
Should I eat below my calculated BMR to lose weight faster?
Eating below BMR is generally discouraged, since BMR represents the minimum energy your body needs for basic functioning at rest — sustained intake below that level isn't a standard recommendation and is worth discussing with a doctor rather than pursuing independently.