Calorie (TDEE)
Daily calorie needs (Mifflin-St Jeor)
Total daily energy expenditure is an estimate of resting metabolism multiplied by a lifestyle factor. This calculator uses the Mifflin-St Jeor equation for the first part and a five-step activity ladder for the second, then offsets 500 kcal in each direction to give loss and gain targets.
Almost all of the uncertainty lives in that multiplier. At the tool's defaults — male, 30, 154 lb, 5 ft 9 in — BMR is 1,649 kcal and each rung of the ladder adds about 288 kcal. That is more than half the 500-kcal deficit the tool subtracts, so choosing the wrong rung turns an intended one-pound-a-week deficit into 212 kcal.
Treat the output as a starting hypothesis to be corrected by three or four weeks of actual weight data. It is not medical or dietetic advice.
Mifflin-St Jeor, and why not Harris-Benedict
- Men:
BMR = 10 x kg + 6.25 x cm - 5 x age + 5 - Women:
BMR = 10 x kg + 6.25 x cm - 5 x age - 161
Mifflin, St Jeor and colleagues published these in 1990, fitted to 498 healthy adults measured by indirect calorimetry. The older Harris-Benedict equations date to 1919, with the Roza and Shizgal revision in 1984:
- Men:
88.362 + 13.397 x kg + 4.799 x cm - 5.677 x age - Women:
447.593 + 9.247 x kg + 3.098 x cm - 4.330 x age
Run the default subject through both: Mifflin-St Jeor gives 1,649 kcal, revised Harris-Benedict gives 1,695 — 46 kcal, about 2.8% higher. Harris-Benedict generally runs high, and Frankenfield's 2005 systematic review in the Journal of the American Dietetic Association found Mifflin-St Jeor landed within 10% of measured resting metabolic rate more often than the alternatives tested, in both non-obese and obese adults. That is why this page offers one equation rather than a menu.
Note what separates the two sex lines: a constant of 166 kcal, and nothing else. At the moderate multiplier that is a 257 kcal/day difference in TDEE between two people identical in age, height and weight.
The default subject, across all five tiers
Male, age 30, 154 lb (69.85 kg), 5 ft 9 in (175.26 cm):
BMR = 10(69.85) + 6.25(175.26) - 5(30) + 5 = 698.5 + 1,095.4 - 150 + 5 = 1,649 kcal
- Sedentary, 1.2: 1,979 kcal
- Lightly active, 1.375: 2,267 kcal
- Moderately active, 1.55: 2,556 kcal (the default, with 2,056 for loss and 3,056 for gain)
- Very active, 1.725: 2,844 kcal
- Athlete or physical job, 1.9: 3,133 kcal
The same person entered as female: BMR 1,483 and maintenance 2,299. And note the span of that list — sedentary to athlete is 1,154 kcal a day for one identical body. No equation can resolve which rung you are on. Only your own weight trend over three or four weeks can.
The activity ladder, and how people misread it
| Level | Multiplier | What it actually describes |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no structured exercise |
| Lightly Active | 1.375 | Light exercise 1-2 days a week |
| Moderately active | 1.55 | Structured exercise 3-5 days a week |
| Very active | 1.725 | Hard exercise 6-7 days a week |
| Athlete / physical job | 1.9 | Manual work plus daily training |
The multiplier describes your whole week, not your workout. A desk job with three gym sessions belongs on the 1.375 row far more often than the 1.55 row, because 165 hours of mostly sitting outweighs three hours of training. Meeting the adult physical activity guideline of 150 to 300 minutes of moderate activity a week is a health target, not a metabolic tier — it puts most people at 1.375.
What the ladder is trying and failing to capture is non-exercise activity thermogenesis: fidgeting, standing, pacing, walking to things. That component varies by up to roughly 2,000 kcal a day between two similarly sized people, which is more than the entire range of this dropdown.
When in doubt, choose the lower tier. Under-eating by 200 kcal is easy to notice and correct; believing in a deficit that does not exist is what stalls people for months.
Where the estimate breaks
Body composition is invisible to it. Mifflin-St Jeor takes scale weight, not lean mass. Two people at 154 lb with 12% and 32% body fat both get 1,649 kcal here. The Katch-McArdle equation, which uses lean mass instead (370 + 21.6 x LBM in kg), gives them 1,698 and 1,396 — a 302 kcal spread this page cannot see. If you know your figure from Body Fat Percentage, treat it as a correction to apply mentally.
The 500 kcal rule rests on a 1958 approximation. The idea that 3,500 kcal equals a pound of body weight overpredicts long-run loss, because expenditure falls as body mass falls. A deficit producing a pound a week in month one produces less in month six at the same intake. NIDDK's Body Weight Planner exists specifically to model that decay, and it is the better tool once you are months into a plan.
Trackers double-count. Wearables and gym machines routinely overstate calories burned, and adding their number on top of a multiplier that already includes your exercise counts the same session twice.
Medication and medical conditions. Thyroid disorders, some antidepressants and antipsychotics, and GLP-1 receptor agonists all shift intake, expenditure or both in ways no population equation captures.
Do not treat BMR as a floor to eat down to. Sustained intake below resting requirement is a clinical decision, not a dieting tactic. The 500 kcal offset here is applied to TDEE, not to BMR, for exactly that reason.
The four numbers on the results panel
- BMR — energy expended at complete rest to keep you alive.
- TDEE — BMR multiplied by your activity tier; the maintenance estimate.
- Weight Loss — TDEE minus 500.
- Weight Gain — TDEE plus 500.
Those two targets are fixed offsets, not percentages, and that has consequences at the edges of the range. 500 kcal is a 20% cut for the default subject and over 35% for a small, sedentary, older adult, which is a very different intervention wearing the same label. Check the deficit as a share of your own TDEE before committing to it.
How to use it without being misled
Set it once, eat to the target for three to four weeks, weigh yourself under consistent conditions, and let the trend correct your multiplier. That feedback loop beats any equation, because it measures you rather than a population you resemble. Recalculate after every 10 to 15 lb of change, since BMR falls as mass falls.
Pair it with BMI for a height-weight screen, Body Fat Percentage to check that a loss is coming off fat rather than lean tissue, and Water Intake if you are adding training volume. If intake matters clinically — an eating disorder history, diabetes, pregnancy, or a medically supervised programme — this page is not the right instrument.
Frequently asked questions
Which activity multiplier should I choose?
Almost certainly one lower than you think. The multiplier covers all 168 hours of your week, so a desk job with three gym sessions is usually 1.375, not 1.55. One tier is worth about 288 kcal a day at the default inputs.
What is the difference between BMR and TDEE?
BMR is what you burn at complete rest. TDEE adds everything else - digestion, daily movement, exercise - by multiplying BMR by an activity factor.
Why does the tool use Mifflin-St Jeor rather than Harris-Benedict?
Harris-Benedict runs high; on the default subject it gives 1,695 kcal against Mifflin's 1,649. Frankenfield's 2005 review found Mifflin-St Jeor came within 10% of measured resting metabolic rate more often than the alternatives.
Does the calculator account for muscle mass?
No. It uses scale weight, so two people at the same weight with very different body composition get identical results. A lean-mass equation such as Katch-McArdle would separate them by roughly 300 kcal.
Will a 500 kcal deficit really lose a pound a week indefinitely?
No. That figure comes from a 3,500-kcal-per-pound approximation and overstates loss over months, because your expenditure falls as your weight falls. Expect the rate to slow and recalculate periodically.
Is it safe to eat below my BMR?
That is a clinical question, not a calculator question. The loss target on this page is set 500 kcal below TDEE, not below BMR, and sustained intake below resting requirement should involve a healthcare professional.
Sources and further reading
Figures and definitions on this page are drawn from the following primary sources. If you find something out of date, tell us and we will correct it.