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BMR Calculator

Enter your age, gender, weight, and height to get far more than a single number. This calculator shows your Basal Metabolic Rate, your Total Daily Energy Expenditure at every activity level, a Harris-Benedict comparison, calorie targets for losing, maintaining, and gaining, plus a daily water target - all from one click.

Enter your age, gender, weight, and height, then click Calculate to see your BMR, TDEE, and calorie targets for every goal

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How to Use the BMR Calculator

1

Enter your age and gender

Type an age between 1 and 120 and pick a gender. The gender changes which formula constant is used, and the age adjusts the category shown in the results.

2

Set the weight unit and enter your weight

Tap kg or lb on the switch, then type your current body weight into the box below it.

3

Set the height unit and enter your height

Switch between cm and ft + in. For feet and inches, fill in both boxes, keeping inches below 12.

4

Click Calculate BMR

The tool computes your Basal Metabolic Rate with the widely trusted Mifflin-St Jeor equation plus a Harris-Benedict comparison.

5

Read your results

See your BMR, a Harris-Benedict comparison, your TDEE at every activity level, calorie targets for losing and gaining, and a daily water target, all in one view.

Your BMR, Your TDEE, and Realistic Calorie Targets - All in One View

Your Basal Metabolic Rate is the number of calories your body burns at complete rest just to keep you alive. Breathing, circulating blood, regulating temperature, and repairing cells all need energy, and BMR accounts for roughly 60 to 75 percent of your total daily burn. That is a huge chunk. But most online BMR tools stop at one number. This one goes much further: it works out your Total Daily Energy Expenditure at every activity level, compares two major formulas so you see how much they disagree, calculates specific calorie targets for losing weight, maintaining, and gaining muscle, and even suggests a daily water target based on your weight. Enter your details and within seconds you will have a practical roadmap instead of a single guess.

The Mifflin-St Jeor Equation Behind the Number

This calculator uses the Mifflin-St Jeor equation, developed in 1990 and now considered the most accurate formula for the general population. For men it is 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age, plus 5. For women it is the same subtraction but minus 161 instead of plus 5. When no gender is selected, the calculator uses the midpoint between the two. Study after study confirms this equation predicts resting energy expenditure more reliably across a wide range of body types than its older rivals.

A Harris-Benedict Comparison: See Two Formulas Side by Side

Most calculators silently pick one formula and never show you the alternative. This one builds in a head-to-head. The result panel shows your Mifflin-St Jeor BMR as the main number and then lists the original 1919 Harris-Benedict estimate alongside it, alongside a plain note explaining which of the two is higher and by how many calories. For a typical adult the older formula tends to run a little warmer, while Mifflin-St Jeor is usually closer to true resting energy. Seeing both helps you judge the confidence of the answer rather than treating one number as gospel.

Your TDEE at Every Activity Level: No More Guessing

BMR only covers rest. Your Total Daily Energy Expenditure adds the thermic effect of food, the energy of everyday movement, and planned exercise. The result panel lists all five standard activity levels - Sedentary at 1.2, Lightly Active at 1.375, Moderately Active at 1.55, Active at 1.725, and Very Active at 1.9 - each with its calorie value for your BMR and a plain description of what that level means. If your BMR is 1,500, sitting at a desk all day puts your total around 1,800, while a physically demanding job and daily training pushes it toward 2,850. That spread is exactly why a single BMR number is only the start.

Calorie Targets for Losing, Maintaining, and Gaining Muscle

The most practical section turns your numbers into four concrete daily targets. To lose about half a kilogram a week, eat roughly 500 calories under your TDEE. To lose about one kilogram a week, eat roughly 1,000 calories under. To maintain, eat to match your TDEE. To build muscle, eat around 250 calories above it, paired with enough protein. Each card also shows a sensible protein target. And there is a safety guard built in: if a loss target would push you below your BMR, this calculator flags the card in orange and refuses to recommend eating that little, because staying above your BMR protects your muscle and energy.

Time Frames and a Daily Water Target

Numbers feel real when you can picture them over time. The result panel shows what a week on each loss target looks like in your chosen unit, and adds a daily water estimate of roughly 33 millilitres per kilogram of body weight. A 70 kg person sees about 2.3 litres a day. Hydration does not burn fat on its own, but adequate water supports the energy, appetite control, and digestion that make a calorie plan easier to follow.

Why BMR Matters for Weight Management

Weight change comes down to the gap between calories in and calories out, and BMR is the largest component of calories out. Underestimate it and your entire plan drifts. Set a target below your BMR and you risk metabolic slowdown, muscle loss, and nutrient shortfalls. Follow generic advice like "eat 1,200 calories" and you may be starving yourself or eating too much without knowing it. BMR gives you a personalised floor, not a random internet number, and the TDEE and target cards on this page show you how to build on it.

What Raises and Lowers Your BMR

Muscle tissue burns more calories at rest than fat, so strength training is one of the few reliable ways to raise BMR over time. Thyroid hormones regulate the rate, which is why untreated hypothyroidism can lower it by 15 percent or more. After about age 30, BMR tends to fall a few percent per decade, mostly from gradual muscle loss - a decline that is far smaller for people who keep training. Fever, pregnancy, and some medications raise it, while strict calorie restriction lowers it as the body adapts. Understanding these levers helps you read your number with context.

This calculator is for informational purposes only and is not medical advice. Always consult a qualified healthcare professional about your nutrition and health.

Frequently Asked Questions

BMR is the calories your body burns at complete rest to keep you alive, and it makes up 60 to 75 percent of your daily burn. TDEE, or Total Daily Energy Expenditure, is BMR plus the thermic effect of food, everyday movement, and planned exercise. This calculator shows your TDEE at all five standard activity levels so you can see both.
The main result uses the Mifflin-St Jeor equation from 1990, widely considered the most accurate formula for the general population. The results also show a Harris-Benedict estimate from 1919 alongside it, so you can see how the two compare and judge the confidence of the answer.
They were built decades apart on different populations. Harris-Benedict tends to run higher, often overestimating calories in overweight people, while Mifflin-St Jeor is usually closer to true resting energy for most people. The result panel tells you which one is higher and by how many calories.
Choose the target that matches your goal. For slow fat loss eat roughly 500 calories under your TDEE, for faster loss about 1,000 under, for maintenance eat to match TDEE, and for muscle gain about 250 above. Each card also lists a protein target. If a loss target would dip below your BMR, it is flagged and capped so you stay above that safety floor.
This calculator estimates about 33 millilitres per kilogram of body weight. A 70 kg person sees roughly 2.3 litres a day. Hydration supports energy, appetite control, and digestion, which help you stick to a calorie plan, though it does not directly cause fat loss.
No. Eating below your BMR means your body does not have enough energy for basic functions, which can trigger metabolic slowdown, muscle loss, fatigue, and hormonal disruption. Create your deficit from your TDEE, not from your BMR, and this calculator flags any target that would drop below your BMR.
Adding muscle through consistent strength training is the most reliable way. Muscle is more metabolically active than fat, so each kilogram you add raises your daily resting burn slightly. Eating enough protein and sleeping well support the process, but resistance training is the biggest lever.
Yes, because a smaller body needs fewer calories. This is normal. A loss of about 10 kg typically lowers BMR by 100 to 150 calories a day. Recalculate after roughly 5 kg or 10 lb of change to keep your targets accurate.
On average men carry more muscle and less body fat at the same height and weight. Muscle is metabolically active, so more muscle means a higher resting burn, typically 10 to 15 percent higher, though individual variation can be significant.
Formula estimates are typically within about 10 percent of a true lab measurement for around 70 percent of people. Muscle mass, thyroid function, medications, and genetics all shift the real number. Treat these figures as a starting point and adjust with real-world weight data over a few weeks.
Recalculate whenever your weight changes by about 5 kg or 10 lb, or if your activity level shifts significantly. For most people tracking fitness goals, every two to three months is enough. There is no need to recalculate for daily fluctuations.
No. Everything is calculated locally in your browser with plain JavaScript. Your age, gender, weight, and height are never stored, transmitted, or logged, and there are no cookies or data collection. Your privacy is fully protected.