FitDexBMR calculator
Basal metabolism is the largest slice of what you burn in a day — for most people 60 to 70% of the total. It isn't earned in the gym or lost on the sofa; it's the fixed bill your heart, brain, liver and kidneys keep paying even while you sleep.
Basal metabolic rate
- Your daily calorie target2,251 kcal
- Your daily water need2.3 L
Capped at the safety floorYour figure fell below this value; we don't show targets under 1,200 kcal for women or 1,500 kcal for men. Intakes that low aren't something to attempt without professional supervision.
Start tracking this goalThis number comes from the very same formula the FitDex app uses. Install the app and you won't be handed a different target.
How is it calculated?
The equation is Mifflin-St Jeor. For men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women the same sum ends in −161 instead of +5, so a 30-year-old woman at 170 cm and 70 kg comes out at 700 + 1062.5 − 150 − 161 = 1451.5. Rounded, 1,452 calories.
The equation has four inputs and three of them are out of your hands: age, sex and height are given. The only input that moves is weight. More precisely, how much of that weight is MUSCLE — but the equation cannot tell muscle from fat, so it never accounts for that share directly, and the reading section below is about how much room the gap takes up.
Why not Harris-Benedict: that equation, published in 1919, came out of a leaner and more active population. Because it systematically overstates resting expenditure against today's body composition, Mifflin-St Jeor was derived in 1990 to correct precisely that bias. It is the clinical default now.
Your total daily expenditure is that number times an activity factor: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very active, 1.9 extreme. The spread can be as large as the BMR itself, which is how a basal rate of 1,452 becomes 1,742 on a sedentary day and 2,759 on an extremely active one. Same body, same day.
How to read your result
The truth behind "my metabolism is slow" is usually this: measured basal rates between two people of the same height, weight and age rarely differ by more than about 10% — on a 1,450-calorie estimate, that's 145 calories. It's a real difference. But it is nowhere near large enough on its own to explain why one person gains and another doesn't, and the actual distance almost always sits in movement and portion size instead.
The one realistic way to RAISE your basal rate is to add muscle. Set the expectation correctly, though: a kilo of muscle burns roughly 13 calories a day, a kilo of fat about 4.5. So four kilos of muscle built over two years add somewhere around 35–50 calories a day. That sounds small because it is — the real payoff of lifting isn't this, it's PRESERVING muscle while you lose weight so expenditure doesn't collapse.
The decline with age is also less dramatic than assumed. Long-run measurements show basal metabolism staying largely flat between 20 and 60, with the drop driven mainly by lost muscle. In other words, the mechanism under "I got older and my metabolism dropped" is usually not age but inactivity.
Eating below this number is not a strategy. Because staying under your basal rate for long stretches lowers expenditure, speeds muscle loss and nearly always ends in an uncontrolled rebound, the number to work from when losing weight isn't BMR at all — it's slightly below the total expenditure you get after applying the activity multiplier.
Frequently asked questions
What's the difference between BMR and TDEE?
BMR is the cost of merely staying alive: energy spent lying still, fasted, in a neutral temperature. TDEE is the whole day: walking, standing, talking, digesting (that costs energy too) and training all sit inside it. The number you set goals against is TDEE. BMR is only the reference point marking the floor.
Does building muscle really speed up my metabolism?
Yes, but far less than expected. At rest, a kilo of muscle burns about 13 calories a day and a kilo of fat about 4.5. Swapping one kilo of fat for one kilo of muscle therefore nets you 8–9 calories a day. The claim that building muscle makes your metabolism take off isn't supported by those figures. Lifting pays off differently: it protects muscle while you're in a deficit, which stops expenditure from collapsing, and the training itself plus recovery burns energy on top.
Does eating too little damage your metabolism?
"Damage" isn't the right word; "adapt" is closer. Under prolonged severe restriction the body measurably lowers expenditure — partly through lost muscle, partly by cutting spontaneous movement: you fidget less, stand less, feel colder. That drop isn't permanent harm and largely reverses once intake returns to normal. But during the return, expenditure is still low while appetite is high, which is how the weight comes back. That's why a moderate deficit is both easier and more durable.
How accurate is this calculation?
Mifflin-St Jeor lands within about ±10% of measured values in healthy adults — so behind an estimate of 1,450 the real figure could sit roughly between 1,300 and 1,600. The error grows at the extremes: it underestimates at very high muscle mass and overestimates at very high body fat. A precise measurement requires indirect calorimetry, a device that reads oxygen and carbon dioxide in your breath. You don't need one. Start from the estimate, watch the scale for two or three weeks, then shift the number to match what actually happened.
Related tools
- Calorie calculatorEnter your height, weight, age and activity level to see your daily calorie needs, basal metabolic rate and macro split in seconds. The same formula as the FitDex app.
- Macro calculatorTurn your daily calorie target into grams of protein, carbohydrate and fat. We publish the ratio we use and why we chose it, instead of offering preset templates with no explanation.
- BMI calculatorEnter your height and weight to see your body mass index, which category it falls in and the healthy weight range for your height. A body fat estimate comes with it — it says what BMI alone cannot.
- Health score calculatorGet your health score out of 100 and see line by line where the points go. In the sample body the score is 59: from a base of 85, BMI takes 20 and body fat takes 11, while activity gives 5 back. Reaching a healthy weight and moving up one activity level takes the same body to 92.
This tool is for information only and is not a substitute for medical diagnosis or treatment. Talk to a healthcare professional before making a lasting change to how you eat.