Straight answers to the most common questions about body mass index, metabolic rate, TDEE, calorie goals, and macros — grouped by topic. For the bigger questions, each answer links to a full guide or the calculator itself.
A BMI in the 18.5–24.9 range is classed as healthy weight for adults, and BMI is weight (kg) divided by height (m) squared, so the healthy weight range scales with your height. On our calculator the readout shows your exact healthy-weight range in kg or lb for your height, rather than a single number.
Metric: take your weight in kilograms and divide it by your height in metres multiplied by itself. For example, 72 kg and 1.75 m: 1.75 × 1.75 = 3.06, then 72 ÷ 3.06 ≈ 23.5. Imperial: multiply weight in pounds by 703, then divide by height in inches squared. The result is the same number either way.
BMI compares your weight to your height and can't tell muscle from fat; body-fat percentage measures how much of your body is actually fat. They answer different questions and are most useful together — see BMI vs body fat for a full comparison.
Muscle is dense, so a very muscular person can have a high BMI while carrying little fat — BMI reads their muscle as excess weight. For muscular people a body-fat measurement is far more meaningful. More in BMI limitations for athletes and older adults.
The healthy BMI range, 18.5–24.9, is the same for adult women regardless of age — BMI categories aren't adjusted by age or sex for adults. What changes with age is body composition, so pairing BMI with a waist or body-fat measurement gives a fuller picture.
Still 18.5–24.9 — the adult BMI bands don't shift with age. However, older adults often lose muscle and gain fat at the same weight, so a 'normal' BMI can hide low muscle mass. Pair it with body-fat and waist measurements; see BMI limitations.
Children's BMI is not read on the adult scale. It's interpreted using age- and sex-specific percentile charts from bodies like the CDC or WHO, because healthy ranges change as children grow. Use a dedicated paediatric BMI percentile tool or ask your child's doctor — the adult categories don't apply.
A BMI of 27 falls in the 'overweight' band (25–29.9). It's a population-level flag, not a diagnosis — a muscular person can sit here with low body fat. Treat it as a prompt to look at body composition and waist measurement rather than a verdict on its own.
Standard BMI categories are not used to assess weight status during pregnancy, because healthy weight gain is expected and the usual bands don't apply. Pre-pregnancy BMI is sometimes used by clinicians to guide recommended gain, but this is a medical judgement. If you're pregnant, follow your healthcare provider's guidance rather than a general BMI calculator.
BMI = 703 × weight (lb) ÷ height (in)². The 703 factor converts pounds-and-inches into the same scale as the metric formula, so both give the same BMI.
BMI = weight (kg) ÷ height (m)². If your height is in centimetres, divide by 100 first to get metres. For example 80 kg at 180 cm (1.8 m): 80 ÷ (1.8 × 1.8) ≈ 24.7.
BMI is a fast, free, no-equipment screen that correlates reasonably well with health risk across a population, and it tracks weight change over time well. Clinicians use it as a starting point, then add other measures (waist, blood markers, history) where it matters — they know its limits.
At a population level, higher BMI is associated with greater risk of conditions like type 2 diabetes, high blood pressure, heart disease, and joint problems. Risk depends on more than the number — where fat sits (abdominal fat carries more risk) and overall fitness matter too. This is general information, not a personal diagnosis.
A BMI of 31 falls in the 'obese' band (30 and above). As always it's a screen, not a diagnosis, and is most informative alongside body-fat and waist measurements and a clinician's view.
No. BMI uses only height and weight, so it can't distinguish muscle from fat. That's its main limitation and why muscular people are often misclassified — a body-fat measurement fills the gap. See BMI vs body fat.
The adult BMI categories (18.5–24.9 healthy, etc.) are the same for both sexes. Men and women differ in typical body composition, which is why body-fat healthy ranges differ by sex — but the BMI bands themselves don't.
It can't see body composition (muscle vs fat), doesn't show where fat is stored, isn't valid for children on the adult scale, and can mislead for the very muscular and for older adults. It's a useful first screen, not a complete assessment — pair it with body fat and waist.
Since BMI is driven by weight, lowering it safely means losing fat at a sustainable rate — roughly 0.5–1% of body weight per week from a moderate calorie deficit, kept above your BMR. See how fast you can safely lose weight and the goal planner.
A BMI of 40 or above is sometimes termed 'severe' or 'morbid' obesity, and 35+ with weight-related health conditions is treated similarly in clinical settings. These are medical classifications best discussed with a healthcare professional rather than self-applied.
Almost certainly muscle. BMI counts all weight the same, so a lean, muscular build reads as 'overweight' despite low body fat. If you train and look fit, trust a body-fat measurement over BMI — see BMI limitations for athletes.
BMR is the energy your body needs at complete rest just to stay alive — heart, lungs, brain, and cell maintenance. It's roughly 60–70% of the calories you burn in a day, before any movement. Calculate yours on the BMR calculator.
Breathing itself is a small part of BMR, but your whole at-rest energy use — BMR — is typically around 1,300–1,800 calories a day for adults, depending on size, sex, age, and body composition. That's what keeps you alive doing nothing.
Very roughly 1,200–1,500 calories a day for many adult women, but it varies widely with weight, height, age, and muscle mass. A formula gives a personal estimate — calculate yours rather than relying on an average.
Often around 1,600–1,900 calories a day for adult men, again with wide variation by size and composition. Men average higher than women mainly because they tend to carry more lean mass.
There's no truly 'exact' figure without lab measurement, but the Mifflin-St Jeor equation gives the best general estimate from weight, height, age, and sex. Our calculator uses it by default; with a body-fat figure it can switch to the lean-mass Katch-McArdle formula.
A 1990 formula that estimates BMR from weight, height, age, and sex, and is the most accurate general predictor in modern comparisons. Full detail on the Mifflin-St Jeor page.
It estimates BMR from the same inputs (weight, height, age, sex) using older coefficients, and tends to read slightly higher than Mifflin-St Jeor. See the comparison on Mifflin vs Harris-Benedict.
BMR is measured under stricter fasted, fully-rested conditions; RMR under looser resting conditions and runs a few percent higher. In everyday use they're used interchangeably. Full explanation in BMR vs RMR.
Partly genuine ageing, but mostly because people lose muscle and move less over the years. The decline is slower than commonly believed — in Mifflin-St Jeor it's about 5 calories per year of age. See does BMR change with age.
The main lever you control is muscle mass — resistance training builds metabolically active tissue. Staying active, eating enough protein, and avoiding prolonged extreme dieting also help preserve BMR. There's no shortcut that meaningfully raises it beyond these.
Yes, modestly. Muscle burns more at rest than fat, so adding lean mass raises BMR — though the effect per kilogram is smaller than fitness marketing often claims. It's still worthwhile, partly because training itself burns energy and protects muscle while dieting.
Often it's simply a smaller body, older age, or less muscle — all reduce BMR. A long history of dieting can also suppress it somewhat (adaptive thermogenesis). If it seems unusually low alongside symptoms like fatigue or cold intolerance, that's worth discussing with a doctor.
Yes. Thyroid hormones are a major regulator of metabolic rate, so an underactive or overactive thyroid can lower or raise BMR. If you suspect a thyroid issue, it's a medical question for your doctor, not something a calculator can assess.
Eating below BMR tends to cost you muscle, energy, and adherence, and it's hard to get enough nutrients — without a faster sustainable result. Set your deficit from TDEE and keep intake at or above BMR. See why you should never eat below your BMR.
Short fasts have little effect on BMR; prolonged or very-low-calorie dieting can lower it somewhat through metabolic adaptation. This is modest and largely reverses when you return to normal eating — not a permanent 'damaged' metabolism. See is my metabolism damaged.
Yes — genetics contribute to individual variation in BMR, which is one reason two people of the same size can differ by a couple hundred calories. It's also why any formula is an estimate. See why two people the same weight differ.
The brain is energy-hungry for its size, using roughly a fifth of resting energy — on the order of 250–350 calories a day for many adults. That's already counted inside your BMR.
Acute stress nudges energy use up slightly through stress hormones, but chronic stress affects weight more through behaviour (sleep, appetite, eating patterns) than through a big BMR change. The day-to-day effect on BMR is small.
Energy use rises a little when the body works to stay warm or fight a fever — metabolic rate increases modestly with body temperature. In normal daily life this is a minor factor compared with body size, composition, and activity.
A BMR formula based on lean body mass, so it needs a body-fat percentage. With a reliable body-fat measurement it can be more accurate than height/weight formulas for people with atypical composition. See the Katch-McArdle page.
TDEE is the total calories you burn in a day: your BMR plus everything you do — movement, exercise, and digesting food. It's your maintenance level, and the number every weight goal is set from. Calculate it on the TDEE calculator.
Multiply your BMR by an activity factor (1.2 sedentary up to 1.9 very active); the part above BMR is your 'active' calories. For a more honest figure, build your real day on the 24-hour activity timeline instead of guessing a label.
Roughly moderate exercise 3–5 days a week, or a reasonably active job. The catch is most desk-workers who train a few times a week are actually 'lightly active' — see how to choose your activity level honestly, the biggest source of wrong TDEE numbers.
Sitting desk work is about 1.5 METs — only modestly above rest — which is why a desk job lands you near the sedentary-to-light end. Build a full day on the activity timeline to see how the hours add up.
Trackers estimate from heart rate, movement, and your profile, then often add 'earned' exercise calories. They tend to overestimate exercise burn (sometimes by 20–50%), so treat their TDEE as a starting point and confirm against your weight trend.
Because TDEE is maintenance — you don't lose weight eating at it; you lose by eating below it. If you're gaining at your estimated TDEE, the estimate (usually the activity multiplier) is too high. See why your TDEE feels too high.
Usually 'lightly active' (1.375) if you otherwise sit at a desk — three sessions are a small slice of total weekly energy. Picking 'moderate' is the classic overestimate. More in choosing an activity level.
There's no official cut-off, but very active days generally run well above 10,000–12,000 steps, while under ~5,000 is sedentary. Steps are a sharper read than activity labels because they're measured, not guessed.
TEF is the energy your body spends digesting and processing food — roughly 10% of intake, and higher for protein than carbs or fat. It's a real part of TDEE and is shown in the breakdown bar on the calculator.
NEAT — non-exercise activity thermogenesis, all your fidgeting, walking, and daily movement — varies enormously between people and can account for several hundred calories a day. It's a big reason two similar people have different TDEEs.
Yes — you burn less on days without training. Many people average their weekly activity into one multiplier and eat consistently, which is simpler and smooths intake. The activity timeline lets you model a specific day.
HIIT runs high on the MET scale (often 8+ METs), so calories ≈ METs × your weight in kg × hours. A 20-minute session is short, though, so the daily total is smaller than it feels — model it in the activity timeline.
Different muscle mass, activity, NEAT, and genetics. Body composition and daily movement vary even at identical weight and height. See why two people the same weight differ.
Maintenance is your TDEE. Start with the calculated estimate, then eat at it for 2–3 weeks and watch your weight trend to confirm. Full method in maintenance calories: how to find and hold yours.
Usually not, if your activity level already reflects your training — that double-counts it, and wearable burns are often overestimated. See should you eat back exercise calories.
A physically demanding job often justifies 'active' (1.725) or even 'very active' (1.9) if it's hard labour all day. Be honest about how much is genuinely strenuous versus standing — and confirm against your weight trend.
Very slightly — your body spends a little energy warming the water — but the effect is tiny, on the order of a handful of calories. It's not a meaningful weight-loss strategy.
About 10% of your daily intake goes to the thermic effect of food, with protein costing the most to process. It's already built into your TDEE and shown in the calculator's breakdown.
1.2 × BMR — for someone with a desk job and little deliberate movement or exercise. If that's you even with occasional workouts, sedentary or lightly active is usually the honest pick.
The most honest approach is to build your actual 24 hours from activity blocks rather than pick a label — our activity timeline does this with MET values — then calibrate against your real weight trend over a few weeks with the tracker.
A pound of fat is roughly 3,500 calories, so about a 500-calorie daily deficit targets ~1 lb a week. Subtract it from your TDEE, not your BMR, and don't go below BMR. See calories to lose weight.
For most adults, a 500-calorie deficit from TDEE is a sensible, sustainable rate as long as intake stays above BMR. It targets roughly 0.5–1 kg a week. People who are smaller or already lean should use a smaller deficit.
A modest surplus — often around 250–500 calories above TDEE — supports muscle gain when paired with resistance training and adequate protein. Bigger surpluses add more fat, not more muscle. See calories to gain weight.
A clean (lean) bulk uses a small surplus to minimise fat gain while building muscle slowly; a dirty bulk uses a large surplus for faster weight gain at the cost of more fat. A lean bulk is usually the better trade for most people.
Divide the weight you want to lose by a safe weekly rate (about 0.5–1% of body weight), remembering the rate slows as you get lighter. The goal planner does this for you and recalculates calories week by week.
Most often intake has crept up (un-weighed food, oils, drinks); next most likely is water retention masking fat loss, then a genuinely lower maintenance as you've slimmed. Full troubleshooting in why weight loss stalls.
Metabolic adaptation is real but modest (around 100–150 calories), and it can't make you gain weight in a genuine deficit. The dramatic 'starvation mode' idea is overstated — see is my metabolism damaged.
Roughly 3,500 calories per pound (about 7,700 per kilogram). It's an approximation, but it's the basis for estimating how a given deficit translates into weight change over time.
Yes — many people lose weight by managing portions, prioritising protein and whole foods, and building habits, without tracking every calorie. Counting is a tool for precision and troubleshooting, not a requirement. A target still helps as a reference.
It depends entirely on her TDEE — there's no universal number. Calculate maintenance, subtract a sensible deficit (often 300–500 calories), and keep intake above BMR. Very low fixed numbers like 1,200 aren't right for everyone and can be too low.
Teenagers are still growing, so calorie restriction shouldn't be self-directed — energy and nutrient needs are high and getting it wrong can affect growth and development. A teen with weight concerns should work with a doctor, paediatrician, or dietitian rather than a general calculator. We don't provide teen deficit targets for that reason.
Find your TDEE, then adjust for your goal: subtract for fat loss, add for muscle gain, or eat at it to maintain. The calculator shows lose/maintain/gain targets at once, with a BMR floor on the deficit.
A small surplus, often around 10–15% above TDEE (roughly 250–400 calories), gains muscle while limiting fat. Track your weight trend and aim for slow, steady gain rather than rapid scale jumps.
It adapts somewhat — BMR falls as you lose weight, plus a modest extra adaptive drop. This is normal and largely reversible. Recalculate as you go and consider periodic maintenance breaks. See metabolic adaptation.
Set protein and fat by body weight first, then let carbs fill the rest, and convert to percentages at the end (protein and carbs are 4 cal/g, fat is 9). Step-by-step in how to split macros.
Higher protein protects muscle while dieting — commonly in the 1.6–2.2 g per kg of body weight range, often toward the upper end during a cut. Detail in how much protein per kg.
1,200 calories is a low, one-size-fits-all figure that is below many adults' BMR, which risks muscle loss, fatigue, and nutrient shortfalls. Rather than a fixed low number, set your deficit from your own TDEE and keep intake above your BMR. Anyone considering a very-low-calorie diet should do so with medical guidance.
Cooking fats are calorie-dense and easy to miss — a tablespoon of oil is around 120 calories. Weigh or measure oils rather than pouring by eye; this is one of the most common reasons a deficit silently shrinks.
The body's tendency to burn slightly less energy during a sustained diet, beyond what weight loss alone predicts — typically around 100–150 calories. It's real but modest and reverses as you return to maintenance. See is my metabolism damaged.
A lighter body burns less, so recalculate your TDEE and reset your target — or better, read your real maintenance from your weight trend. See when to recalculate your TDEE and the tracker.
Macros are the three energy-providing nutrients: protein, carbohydrate, and fat. To calculate them, set protein and fat from your body weight, then fill the remaining calories with carbs. Full method in how to split macros, and the meal macro decoder turns targets into grams of food.
Roughly 0.7–1.0 g per pound of body weight (about 1.6–2.2 g per kg) suits most active people building or keeping muscle. See how much protein per kg for what each part of the range is for.
There's no single ideal split — total calories drive fat loss. That said, keeping protein high (to protect muscle and stay full) and filling the rest with carbs and fat to preference works well. Prioritise the protein target over chasing exact percentages.
4 calories per gram.
9 calories per gram — more than double protein or carbs, which is why fats are easy to over-consume by volume.
4 calories per gram.
A common high-protein, low-carb split lands somewhere around 40% protein, 30% carbs, 30% fat, but the exact ratio matters less than hitting your protein target and total calories. Set protein and fat first, then adjust carbs down to taste.
Keto sets carbs very low (often under ~50 g/day), protein moderate, and fat high to fill remaining calories. Set carbs to your keto limit, protein by body weight, and the rest as fat. General nutrition planning like this lives in more depth on our sister site CaloriesKit.
A common guideline is about 14 g of fibre per 1,000 calories eaten, so roughly 25–35 g a day for many adults. Fibre aids fullness and digestion — useful when dieting. This is general guidance, not a personal prescription.
Dietary fat supports hormones and the absorption of fat-soluble vitamins, so a minimum intake matters even in a deficit — commonly around 0.6–1.0 g per kg of body weight. Cutting fat too low can affect how you feel, not just your calories.
Translate your macro targets into grams of specific foods, then weigh them — that's exactly what our meal macro decoder does: pick foods and it computes the grams of each to hit your protein, carb, and fat targets.
Lean options include chicken breast, white fish, egg whites, non-fat Greek yoghurt, and many legumes. These let you hit protein without spending much of your fat budget. The meal macro decoder includes lean protein sources to build from.
Add up the macros of each raw ingredient by weight, then divide by the number of servings. Weighing ingredients raw is more accurate than estimating cooked portions. A food scale plus the meal macro decoder makes this straightforward.
Alcohol provides 7 calories per gram and isn't one of the three macros, but those calories still count toward your daily total and can crowd out a deficit. If you drink, account for it in your calories.
Endurance athletes generally need more carbohydrate to fuel training — often a substantial share of intake. Set protein and fat first, then allocate most of the remaining calories to carbs. Sport-specific fuelling is covered in more depth on CaloriesKit.
Bodybuilders typically prioritise high protein (often toward 2.2 g/kg), moderate fat, and carbs adjusted around training. As always the protein target and total calories matter more than a fixed percentage split. See protein per kg.
Adjust portion sizes proportionally to fit the protein, carb, and fat you have left for the day. The meal macro decoder handles this directly — set your remaining target and it solves the grams of each food to fit.
Bloating is more often from fibre, certain foods, or eating quickly than from protein itself. Some people react to specific protein sources (like whey) — if it's persistent or uncomfortable, it's worth discussing with a healthcare professional.
Simple carbs are quickly digested sugars; complex carbs (whole grains, legumes, vegetables) digest more slowly and usually bring fibre and nutrients. Both count the same for calories, but complex carbs tend to be more filling and nutritious.
Weigh foods raw, look up the macros per 100 g, and scale to your portion — raw weighing is more consistent than cooked because cooking changes water content. Feed the numbers into the meal macro decoder to hit your targets exactly.