How this instrument works
Maintenance calories are the daily energy intake that, on average, neither adds nor removes body weight over time — the number a diet plan typically starts from before adjusting up or down toward a goal. This instrument builds it in two stages: it computes basal metabolic rate (BMR) first, using the Mifflin-St Jeor equation, then multiplies that resting figure by an activity factor drawn from five tiers running from a desk job with little exercise to twice-daily athletic training.
The resting half comes from a 1990 study in which Mifflin, St Jeor and colleagues measured 498 healthy adults by indirect calorimetry and fit a simple linear equation to the results, sex handled with a single additive constant. The activity-multiplier half is a longstanding convention in clinical dietetics — scaling resting metabolism by an activity ratio to approximate a full day's energy cost, rather than trying to track every individual movement.
Both halves predict a population average for someone your size, sex and age, not a direct measurement of your own metabolism. The only way to confirm true daily energy expenditure is doubly labelled water tracked over roughly two weeks — laboratory work well beyond four numbers on a form. Treat this figure as a reasonable starting point to weigh against how your own body weight trends over several weeks, and adjust from there rather than treating it as exact.
- Set Sex — it changes a closing constant in the resting-metabolism equation, +5 for male or −161 for female.
- Enter Weight and Height, switching either unit menu to pounds, stone, feet or inches if you don't use metric.
- Enter Age in years; each additional year removes five kcal from the resting estimate.
- Pick Activity level from five tiers — sedentary, light, moderate, very active or athlete.
- Read Basal metabolic rate first, then Maintenance calories below it — that second figure is BMR times your chosen activity tier.
Worked example — 80 kg, 180 cm, age 40, lightly active man
Enter 80 kilograms, 180 centimetres, age 40, Sex set to male, and Activity level set to Light. The resting equation runs 10 × 80 + 6.25 × 180 − 5 × 40 + 5, which is 800 + 1,125 − 200 + 5 — a basal metabolic rate of 1,730 kcal per day, the cost of this body doing nothing at all.
The Light tier carries a multiplier of 1.375, for someone exercising roughly one to three days a week. Multiplying 1,730 by 1.375 gives 2,378.75 kcal per day — this instrument's maintenance calorie estimate, the intake expected to hold this person's weight steady if their week matches that description.
Questions
Is maintenance calorie the same thing as TDEE?
Yes — maintenance calories and total daily energy expenditure (TDEE) describe the identical quantity under two names that are both common in everyday search and conversation. This calculator uses the same Mifflin-St Jeor formula and the same five-tier activity table as this site's own TDEE calculator, for exactly this reason: the underlying math doesn't change just because the page is titled differently.
How accurate is this estimate?
It's a population-average prediction, not a direct measurement of you — expect it to sit within roughly 10 to 20 percent of a lab measurement like doubly labelled water. Use the output as a starting point, then adjust any intake plan built from it based on how your own weight trends over two or three weeks, a more reliable signal for your specific body than any single formula.
Why does another calculator give me a different maintenance calorie number for the same body?
Calculators disagree because they mix different underlying pieces: some use the older 1919 Harris-Benedict equation instead of Mifflin-St Jeor, others use Katch-McArdle (which needs a body-fat percentage), and activity-tier multipliers vary slightly between sites. A gap of one or two hundred kcal between two reasonable tools is normal and doesn't mean either is wrong.
Should I eat exactly at my maintenance calorie number?
That figure is an estimate of maintenance, not an instruction. Whether to eat above, at, or below it depends on a goal this calculator has no way of knowing, and the underlying estimate carries meaningful uncertainty in both directions — treat it as a number to adjust from once you see how your weight actually responds, not a target to hit precisely.
What happens if I pick the wrong activity tier?
The multiplier scales your entire resting metabolism, not just exercise calories, so picking one tier too high or low can shift the final number by several hundred kcal a day. If you're unsure between two tiers, starting with the lower one and adjusting upward based on real weight trend over a few weeks is usually safer than guessing high.
Does this account for muscle mass or body composition?
No — Mifflin-St Jeor uses only weight, height, age and sex, not lean mass or body fat percentage, which is part of why it's a population average rather than an individual measurement. The Katch-McArdle equation is the standard alternative when a reasonably accurate body-fat percentage is available, since it estimates resting metabolism from lean mass directly instead.
References
- Mifflin et al. 1990, Am J Clin Nutr — original BMR equation (PubMed)
- NIH NIDDK — Body Weight Planner
- WHO — Physical activity fact sheet
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.