Getting a resting rate and a daily burn you can plan against
1. Enter age, sex, height and weight
Switch between metric and imperial freely — the values convert rather than resetting. In the previous build, changing units silently threw away everything you had typed and showed a different default person, which is how people ended up planning their week around a stranger’s numbers.
2. Choose the activity level that matches your real week
Not the week you intend to have. Most people overestimate here, and the multiplier is applied to your entire resting rate, so one step too far up the scale can add three or four hundred calories a day to your estimate. If you are between two levels, take the lower one and adjust after a fortnight of real evidence.
3. Add your body fat percentage if you know it
Optional, and it unlocks the two equations that use lean mass rather than total weight — Katch-McArdle and Cunningham. If you have a reasonable estimate from our body fat calculator or a DEXA scan, these are usually the better predictors, particularly at the lean and the heavy ends.
4. Read your BMR, then your TDEE
BMR is what you would burn lying still all day. TDEE is BMR multiplied by your activity factor and is the number that actually matters for eating. The gap between them is usually four hundred to a thousand calories, which is why quoting BMR as a calorie target is such a damaging mistake.
5. Look at the spread across the four equations
All four are shown, and so is the distance between the highest and lowest. That spread — often 150 to 250 calories — is the honest measure of how precise any single prediction is. It is not a defect in the tool; it is the state of the science.
6. Read the targets, and any floor warning attached to them
The maintenance, loss and gain targets now follow the activity level you actually chose. If a target has been held at a safety floor rather than calculated down, the tool says so in plain words and explains why, instead of printing a number that would be unsafe to eat to.
What basal metabolic rate actually measures
Your basal metabolic rate is the energy your body uses to stay alive at complete rest: keeping your heart beating, your lungs moving, your kidneys filtering, your brain running and your body at temperature. It is measured in a laboratory after an overnight fast, lying still, awake, in a thermally neutral room. For most adults it accounts for somewhere between sixty and seventy-five per cent of everything they burn in a day.
You will also see the term resting metabolic rate, or RMR. It is measured under slightly less strict conditions and typically comes out a few per cent higher. The equations on this page are generally described as predicting one or the other depending on the paper; the difference is small compared with the error in predicting either from height and weight.
The rest of your daily burn is made up of the thermic effect of food — roughly ten per cent of what you eat, spent digesting it — deliberate exercise, and non-exercise activity thermogenesis, which is everything from walking to the shop to fidgeting. That last category varies enormously between people and is the main reason two people of identical size can have daily burns hundreds of calories apart.
The four equations, and why we show all of them
Mifflin-St Jeor (1990) is the default and the one most dietetic practice uses. It was published in the American Journal of Clinical Nutrition in February 1990, derived from 498 healthy adults aged 19 to 78, including both normal-weight and obese participants. A systematic review by Frankenfield and colleagues in the Journal of the American Dietetic Association in May 2005 compared the available equations and found Mifflin-St Jeor the most reliable for healthy adults, which is why it is the headline here.
Revised Harris-Benedict is the 1919 original as re-fitted by Roza and Shizgal in the American Journal of Clinical Nutrition in July 1984. The 1919 equations were derived from a population that ate and moved differently from a modern one, and tend to overestimate; the revision corrects some of that but still typically reads a little above Mifflin-St Jeor.
Katch-McArdle uses lean body mass rather than total weight, so it needs a body fat percentage. Because muscle is metabolically active and fat is much less so, this is conceptually the better approach — provided your body fat figure is any good. Feed it a bad estimate and you get a confidently wrong answer.
Cunningham (1980), published in the American Journal of Clinical Nutrition in November 1980, also works from lean mass and reads higher than Katch-McArdle. It is often preferred for athletic populations, where the general-population equations tend to underestimate.
Showing one number would be more comfortable and less honest. Prediction equations for resting metabolism carry an error of roughly ten per cent for most people and considerably more for some. The spread between four reasonable methods is the clearest way to communicate that without a paragraph of statistics.
Activity multipliers, and the mistake almost everyone makes
TDEE is BMR multiplied by an activity factor. The conventional scale runs approximately:
- Sedentary (×1.2) — desk work, little deliberate exercise.
- Lightly active (×1.375) — light exercise one to three days a week.
- Moderately active (×1.55) — moderate exercise three to five days a week.
- Very active (×1.725) — hard exercise six or seven days a week.
- Extra active (×1.9) — hard daily training, or a physically demanding job on top of training.
These multipliers are broad brush and they are where most of the error in a TDEE estimate comes from. A single step up the scale is worth several hundred calories a day for an average adult. Three gym sessions a week alongside a desk job and a car commute is “lightly active” for most people, not “moderately active” — an hour of exercise does not undo twenty-three hours of sitting.
This matters more than usual on this page, because in the previous build the multiplier was ignored entirely when the targets were calculated. The line var tdeeMod = primary * 1.55 hardwired the moderate factor into the projections while the table above offered you five choices. For a 70 kg, 175 cm, 30-year-old man, a sedentary visitor was handed a fat-loss target 577 calories a day too high — enough to prevent the loss the panel was promising him — and a very active one was handed a target 577 too low. The targets now use the level you actually select.
Why some targets stop at a floor and say so
Fixing the multiplier bug exposed a second one that had been hidden behind it. With no floor on the deficit, the arithmetic could produce targets below the level at which unsupervised dieting is considered safe. A 55-year-old woman of 150 cm and 45 kg was shown a fat-loss target of 975 calories a day — below her own basal rate of 952, meaning the recommendation was to eat less than her body needs to run its organs. At the sedentary setting, the same arithmetic produced 642.
Very low calorie diets exist, they have legitimate clinical uses, and they are conducted under medical supervision with monitoring, because at those intakes the risks include muscle and bone loss, gallstones, electrolyte disturbance, cardiac arrhythmia and nutritional deficiency. A web page is not a supervising clinician. Targets are now held at a floor — commonly cited as around 1,200 calories a day for women and 1,500 for men for unsupervised dieting — and when the floor has been applied, the tool says so and explains why rather than quietly printing the higher number as though nothing happened.
The “500 calories a day is a pound a week” rule, and where it breaks
That rule comes from a 1958 paper by Max Wishnofsky, which established the figure of 3,500 calories per pound of body fat. The arithmetic is sound as far as it goes, and over the first few weeks the prediction holds up reasonably well.
It increasingly overstates loss after that, for a straightforward reason: a smaller body burns less. As you lose weight, your BMR falls, your TDEE falls with it, and the deficit you started with quietly shrinks. Applied linearly, the rule predicts that a sustained 500-calorie deficit produces about 23 kg of loss in a year. Real-world outcomes are consistently and substantially below that, and the shortfall is not a failure of willpower — it is physiology doing what it always does.
The tool names the rule rather than presenting its output as a flat projection. If you want a model that accounts for the moving target, the NIDDK Body Weight Planner is built on a dynamic model developed at the National Institutes of Health and will give you a far more realistic trajectory than any single multiplication can.
Protein, and why the old figure was inflated
The previous version printed a single protein figure of about 1.8 g per kilogram of total body weight, with no source. Two problems. First, one number is not a recommendation — requirements differ enormously between a sedentary older adult and someone in a hard training block. Second, calculating from total weight inflates the target for anyone carrying substantial body fat, because adipose tissue does not have the same protein requirement as lean tissue. For someone at 35 per cent body fat, that difference is considerable.
The page now gives a range with its source. The International Society of Sports Nutrition’s position stand on protein and exercise, published in 2017, supports roughly 1.4 to 2.0 g per kilogram per day for building and maintaining muscle in physically active people, with higher intakes appropriate during periods of energy restriction to protect lean mass. General population recommendations for sedentary adults sit far lower, at around 0.8 g per kilogram. Where you have entered a body fat percentage, the tool also computes the figure from lean mass, which is the more defensible basis.
How accurate is any of this?
For most healthy adults, a good prediction equation lands within about ten per cent of measured resting metabolism. Ten per cent of a 1,600-calorie BMR is 160 calories, and the activity multiplier then amplifies whatever error you started with.
The equations are least reliable for people at the extremes of body size, for the very muscular, for older adults, during pregnancy and breastfeeding, and for anyone with a thyroid disorder or taking medication that affects metabolism. If you have a diagnosed metabolic or endocrine condition, the number on this page is a starting guess and your clinical team’s advice is not.
The practical approach is to treat your TDEE as a hypothesis. Eat at it for two to three weeks, weigh yourself consistently, and adjust from what actually happened. Your own body’s response over a fortnight is better evidence than any equation.
What this page is not
It is not a diet plan, a diagnosis or medical advice. It converts your measurements into an energy estimate using published equations, names them, and shows how much they disagree. It will not tell you to lose weight, and it will not produce a target below the level at which eating without supervision stops being safe.
If you are pregnant or breastfeeding, under 18, managing diabetes, recovering from illness or surgery, or have any history of an eating disorder, please treat these numbers as background reading only and take your targets from a doctor or a registered dietitian.
Your numbers never leave the browser
Everything is computed locally in JavaScript. Age, sex, height, weight, activity level and body fat percentage are never transmitted, stored or logged, and the page continues to work offline once loaded.
Questions people ask about BMR and TDEE
Should I eat my BMR or my TDEE?
Your TDEE, adjusted for your goal. BMR is what you burn doing nothing at all; eating at it while living a normal life produces a large unintended deficit. Quoting BMR as a calorie target is one of the most common and most harmful errors in this corner of the internet.
Why did my TDEE change when I switched units?
It should not, and now it does not. The old build had separate age inputs for the metric and imperial panels that never synchronised, so switching units silently loaded different defaults. Values now convert properly.
Which equation should I trust?
Mifflin-St Jeor unless you have a reliable body fat measurement, in which case Katch-McArdle or Cunningham are usually better. The systematic review evidence supports Mifflin-St Jeor as the best general-purpose choice for healthy adults.
Why is my calculated BMR lower than I expected?
Most often because the equations account for age and sex, and both reduce the prediction — resting metabolism declines with age largely through loss of lean mass. If you carry more muscle than average for your size, expect the general-population equations to read low, and use the lean-mass ones.
Can I speed up my metabolism?
Meaningfully, only by adding lean tissue, which is slow and requires resistance training and adequate protein. The much larger lever is the other side of TDEE: daily movement outside formal exercise. Nothing you can drink changes your basal rate to a degree that matters.
Why does the tool refuse to go below a certain number of calories?
Because below roughly 1,200 calories a day for women and 1,500 for men, dieting without medical supervision carries real risks — muscle and bone loss, gallstones, electrolyte disturbance and nutritional deficiency. The tool holds the target at that floor and tells you it has done so.
How much protein should I actually eat?
For a physically active adult, roughly 1.4 to 2.0 g per kilogram per day, and toward the upper end while in a deficit to protect lean mass. Sedentary adults need far less. Where body fat is known, calculating from lean mass gives a more sensible figure than using total weight.
Is a 500-calorie deficit really half a kilogram a week?
Early on, roughly. Over months, no — the deficit shrinks as you do. Expect the rate of loss to slow even if your eating does not change, and plan for that rather than treating it as failure.
Do you store my details?
No. Nothing is saved or transmitted.
Sources behind these numbers
- Mifflin MD, St Jeor ST et al, “A new predictive equation for resting energy expenditure in healthy individuals”, American Journal of Clinical Nutrition, February 1990 (PMID 2305711), n = 498, aged 19 to 78.
- Roza AM, Shizgal HM, “The Harris Benedict equation reevaluated”, American Journal of Clinical Nutrition, July 1984 (PMID 6741850).
- Cunningham JJ, “A reanalysis of the factors influencing basal metabolic rate in normal adults”, American Journal of Clinical Nutrition, November 1980 (PMID 7435418).
- Frankenfield D, Roth-Yousey L, Compher C, “Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review”, Journal of the American Dietetic Association, May 2005 (PMID 15883556).
- Wishnofsky M, 1958 — the origin of the 3,500-calorie-per-pound rule, and its limits.
- Jager R et al, “International Society of Sports Nutrition Position Stand: protein and exercise”, Journal of the International Society of Sports Nutrition, 2017, for the 1.4 to 2.0 g/kg range.
- NIDDK Body Weight Planner — a dynamic NIH model, better than any linear rule for projecting weight change.
- NHS — healthy weight, for the UK framing of safe rates of change.
- CDC — about healthy weight and growth.
Tools people open next to this one
- Calories Burned Calculator — MET-based figures for specific activities, rather than a blanket multiplier.
- Ideal Weight Calculator — four formulas and how far apart they sit.
- Water Intake Calculator — the other daily figure people plan around.
