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Calorie Calculator
Estimate your daily calorie needs — to maintain, lose or gain weight — using the Mifflin–St Jeor equation and your activity level, instantly in your browser.
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Quick Answer
Enter your age, weight, height, sex and activity level and the tool estimates your daily calorie needs — the calories to maintain your weight — plus targets to lose or gain about half a kilogram a week. It uses the Mifflin–St Jeor equation for your resting burn, multiplied by an activity factor. These are estimates, not a meal plan or medical advice. It runs entirely in your browser; nothing is uploaded.
What the Calorie Calculator Does
This tool estimates how many calories you need in a day. It works out your resting burn, scales it by how active you are to get your total daily energy use, and then shows targets for maintaining your weight and for losing or gaining around half a kilogram a week.
It is the quick way to put a number on your daily calorie target — a starting point for a diet or a fitness goal, based on your own details rather than a generic figure.
How It Works
The tool first estimates your Basal Metabolic Rate — your rest-only calorie burn — with the Mifflin–St Jeor equation, the same calculation a BMR calculator uses. It then multiplies that by an activity factor, from about 1.2 for a sedentary day up to 1.9 for very active, to get your Total Daily Energy Expenditure: the calories you use in a typical day.
For weight goals, it adjusts that maintenance figure by 500 calories a day. A deficit of 500 a day is roughly half a kilogram a week, based on the rule of thumb that about 7,700 calories equate to a kilogram of body weight. Eating below maintenance aims to lose; above it aims to gain.
Methodology
- Estimate BMR. Use the Mifflin–St Jeor equation from your age, weight, height and sex.
- Apply activity. Multiply BMR by your activity factor to get total daily energy use.
- Set maintenance. That total is the calories to maintain your weight.
- Adjust for goals. Subtract or add 500 calories a day for losing or gaining about half a kilogram a week.
Daily calories (TDEE and goals)
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + s (s = +5 men, −161 women)
maintain = BMR × activity factor (1.2 to 1.9)
lose ≈ maintain − 500 gain ≈ maintain + 500 (≈ 0.5 kg per week)Worked example
male, 30 y, 70 kg, 175 cm, moderate → maintain ≈ 2,556 kcal · lose ≈ 2,056 · gain ≈ 3,056The 500-a-day adjustment comes from the rough rule that about 7,700 kcal equal a kilogram. It is a simplification — the body adapts, so real weight change varies.
Assumptions
- Resting burn is estimated with the Mifflin–St Jeor equation, the same as a BMR calculator; the activity factor scales it to a daily total.
- The 500-calorie adjustment for half a kilogram a week is based on the rough 7,700-kcal-per-kilogram rule, which is a simplification.
- Inputs are metric, the figures are estimates, and this is general information, not a personalised meal plan or medical advice.
Standards & references
- Total Daily Energy Expenditure — TDEE is the calories you use in a day — your resting burn times an activity factor. It is the maintenance figure: eating it keeps your weight roughly steady.
- Mifflin–St Jeor for BMR — The resting burn comes from the Mifflin–St Jeor equation, the modern standard, accurate within about 5% for most people. The calorie targets build directly on it.
- The calorie rule of thumb — About 7,700 calories are often equated with a kilogram of body weight (3,500 per pound). A 500-a-day change is roughly half a kilogram a week — a simplification, not an exact law.
Accuracy & Limitations
As a starting point, the figures are sound: the Mifflin–St Jeor base is accurate within about 5% for most people, and the activity multiplier gives a reasonable daily estimate.
The weight-goal targets are rougher. The 500-a-day rule treats the body like a simple calorie bank, but metabolism adapts as you eat less, not all of a deficit is fat, and real weight change varies from person to person. Expect the actual result to differ.
The activity factor is the biggest source of error, because people often misjudge how active they are. If your weight does not move as expected after a few weeks, adjust your estimate up or down rather than the formula.
It is general information, not a personalised plan. Very muscular people may need more than the estimate, and anyone with a medical condition, or who is pregnant, should consult a professional rather than rely on a calculator.
Real-World Use Cases
Setting a daily target
Find calories to maintain, lose or gain weight.
Starting a diet
Get a calorie goal based on your own details.
Planning a fitness goal
Estimate intake for a weight change over time.
Understanding your needs
See how activity changes your daily calories.
When to use it — and when not to
Good for
- A daily calorie target to start from
- Maintain, lose or gain estimates
- Basing a goal on your own details
- Seeing how activity affects needs
Not the best choice for
- An exact, guaranteed weight-change plan
- Medical or clinical nutrition needs
- Pregnancy or specific health conditions
- A personalised meal plan
For a precise plan or a medical condition, a dietitian tailors targets to you. For tracking, log your intake and adjust based on real results over a few weeks, since the body adapts. This tool gives an evidence-based starting estimate.
Frequently Asked Questions
How does it estimate my daily calories?
It calculates your resting burn with the Mifflin–St Jeor equation, then multiplies by an activity factor for your total daily energy use. That total is your maintenance calories, and the goals adjust it by 500 a day.
Why subtract 500 calories to lose weight?
Because about 7,700 calories are roughly equal to a kilogram of body weight, a deficit of 500 a day is about half a kilogram a week. It is a rule of thumb, not an exact law, so real results vary.
Is the weight-loss target guaranteed?
No. The body adapts as you eat less, not all of a deficit is fat, and individual metabolism differs. Treat the target as a starting point and adjust based on what actually happens over a few weeks.
What activity level should I choose?
Pick the one that matches a typical week honestly. People often overestimate, so if unsure, choose a lower level. If your weight does not change as expected, adjust your activity estimate.
Is this the same as the BMR calculator?
It uses the same Mifflin–St Jeor resting burn as the BMR calculator, then adds an activity factor and weight-goal targets. The BMR calculator stops at the resting figure; this one estimates full daily needs.
Can I lose weight faster with a bigger deficit?
A larger deficit can lose weight faster but is harder to sustain and risks losing muscle and slowing metabolism. A moderate deficit, around 500 a day, is generally more sustainable and is what the goal target uses.
Does it account for muscle?
Not directly. The Mifflin–St Jeor base uses weight, height, age and sex, not body composition, so very muscular people may need more than the estimate. Adjust upward if you carry a lot of muscle.
Can I use imperial units?
The formula uses kilograms and centimetres. Convert first — about 0.45 kg per pound and 2.54 cm per inch — so the resting burn and the calorie targets come out correctly.
Is this safe to follow for weight loss?
It is a general estimate, not medical advice. Very low intakes can be unsafe, and anyone with a health condition, or who is pregnant, should consult a professional before changing their diet.
Why did my weight not change at the target?
Estimates are not exact, and the body adapts. The activity factor or the calorie rule may not match you precisely. Track your intake and weight over a few weeks and adjust the target based on the real trend.
Is my data uploaded?
No. The calculation runs entirely in your browser. Nothing is sent to a server, so your details stay on your device.
Does it give a meal plan?
No. It gives a daily calorie target. How you meet it — the balance of protein, carbohydrate and fat, and the foods you choose — is up to you or a dietitian who can plan it properly.
References
Estimates daily calories as Mifflin–St Jeor BMR times an activity factor, with weight-goal targets from the rough 7,700-kcal-per-kilogram rule; honest that these are estimates, not a meal plan.
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