The whole method, in order, with the research each piece rests on. Nothing here is proprietary — you should be able to reproduce every number with a calculator.
Your body spends energy on four things. Add them up and you have your daily total — what the fitness world calls TDEE. Eat that much and your weight holds; eat less and you lose; eat more and you gain.
Most calculators collapse all of this into one activity multiplier picked from a dropdown. We break it apart instead, because you can sanity-check four small numbers in a way you can't sanity-check one big one.
What you'd burn lying still all day: heart, lungs, brain, kidneys, body heat. Usually 60–70% of the total, which is why activity alone is such a slow lever.
Processing what you eat costs energy — roughly a tenth of it. Protein costs the most to break down, fat the least.
Walking to the car, standing, cooking, carrying shopping, fidgeting. It varies enormously between people — often by several hundred calories a day between two people with the same job title.
Deliberate exercise, averaged over the week. Usually the smallest of the four, which surprises people.
This is the single biggest reason calculators come out too high.
A conventional tool gives you one dropdown: sedentary, lightly active, moderately active, and so on. The descriptions usually mention exercise — "moderate exercise 3–5 days a week" — so you pick a level that includes your gym habit. Then, because you also logged that gym session on your watch, you count it again. Your 300-calorie workout has quietly become 600.
So we split the question. Question two is your job, your commute and your evenings, with workouts explicitly excluded. Question three is training. Nothing gets counted twice.
We also only count the extra energy a workout costs. An hour of jogging might burn 600 calories in total, but you'd have burned about 80 of those lying on the sofa, and those 80 are already in the first line. Counting the gross figure inflates the total.
Four steps. Weight in kilos, height in centimetres, age in years throughout.
men: (10 × kg) + (6.25 × cm) − (5 × age) + 5women: (10 × kg) + (6.25 × cm) − (5 × age) − 161
This is the Mifflin-St Jeor equation. Of the common options it lands within 10% of a person's measured resting rate more often than the alternatives, which is why clinicians reach for it over the older Harris-Benedict.
370 + (21.6 × lean kg), where lean kg = kg × (1 − bodyfat%)
This is Katch-McArdle. It ignores age and sex entirely and works from muscle mass, which is the thing actually doing the burning. It's better than Mifflin-St Jeor at the extremes — very lean or very heavy bodies — but only if your body fat figure is real. A guess makes it worse, which is why the field is optional and stays empty by default.
resting × 0.10 mostly sittingresting × 0.25 sitting, but up and aboutresting × 0.45 on your feet most of the dayresting × 0.70 physical work
Scaling to resting rate rather than using a flat number means a larger body gets a larger figure, which is right — moving more mass costs more.
(METs − 1) × 3.5 × kg ÷ 200 × minutesdaily average = per session × sessions ÷ 7
A MET is a multiple of resting energy use, defined as 3.5 mL of oxygen per kilo per minute. Easy is 3.5 METs, moderate 6, hard 8.5 — mid-range values for those intensity bands from the 2024 Adult Compendium. Subtracting 1 is what strips out the resting portion already counted in step 1.
total = (resting + moving + workouts) ÷ 0.9digestion = total − resting − moving − workouts
Digestion costs about 10% of what you eat, not 10% of what you burn — so it's a share of the final figure, which means dividing rather than multiplying. Research puts a mixed diet at 5–15%; we use 10%. A very high-protein diet sits nearer the top of that range.
Sanity check: for a sedentary adult this whole chain produces a total about 1.22 times resting energy, and for someone with a physical job who also trains hard, about 1.9. Those match the conventional activity multipliers, which is what you'd hope — we've arrived at the same place by a route you can inspect.
The twelve-week chart doesn't draw a straight line, and that's deliberate.
The familiar rule — 3,500 calories per pound, or 7,700 per kilo — assumes your energy needs never change. They do. As you get lighter you burn less, so a fixed intake produces a shrinking deficit and progress flattens. Applied over months, the flat rule substantially overstates what actually happens; in supervised trials people lost meaningfully less than it predicted, and the error compounds the longer you run it.
So the chart recalculates your whole daily total each week at your new weight, keeping your intake fixed, and plots the result. It still isn't a promise — it can't see your adherence, your sleep, or the metabolic adaptation that comes with sustained dieting — but it bends in the right direction, and it makes the case for rechecking your numbers as you go.
Two limits are built in, and the page tells you when it hits them.
It also caps a surplus at 600 calories a day, because beyond that most of the extra arrives as fat rather than muscle.
Honestly: it's a good starting estimate and nothing more.
These equations were built from population averages. Even the better ones fall outside 10% of a person's measured resting rate a substantial share of the time — and 10% of 2,400 calories is 240 either way. Layer activity on top and the uncertainty grows. Genetics, body composition, hormones, medication, sleep, illness and dieting history all move the real number in ways a formula can't see.
That's not a reason to skip the calculation. It's a reason to treat the output as an opening bid and let two weeks of real weigh-ins correct it. The check-in steps on the calculator page are the part that actually gets you an accurate number.
We're Melton Studios. We built this for ourselves, because every calorie calculator we could find handed over a single number with no way to check it, and most of them quietly counted our workouts twice. We wanted one that showed its working. Having built it, publishing it seemed better than keeping it.
We're not doctors or dietitians, and we don't claim to be. Everything here is assembled from published research, cited on this page so you can go and read it yourself rather than take our word for anything. Where the evidence disagrees with the convention — as it does on the calories-per-pound rule, and on how much a standing desk is really worth — we've said so rather than quietly using the more flattering number.
If you spot something wrong, we'd like to know: [email protected]. Corrections are more welcome than compliments.
The jargon you'll meet everywhere else, translated.
A unit of energy, the same way a mile is a unit of distance. Food carries energy in; your body spends it keeping you running. Nothing more mystical than that.
Total What Do I Burn Expenditure — the industry's name for "your daily total". All four line items added together: everything you burn in twenty-four hours.
Basal (or Resting) Metabolic Rate: the "staying alive" line. What you'd burn lying perfectly still all day. For most people it's 60–70% of the total, which is why "boosting your metabolism" through activity alone is such hard work.
Non-Exercise Activity Thermogenesis — the "everyday moving" line. Walking to the bus, standing, cleaning, fidgeting. It varies enormously between people and is usually far bigger than their workouts, which is why question two matters more than question three.
Thermic Effect of Food — the "digesting food" line. Digestion itself costs energy, roughly a tenth of what you eat. Protein is the most expensive to process, which is one reason higher-protein diets tend to work slightly better than the calories alone suggest.
Metabolic Equivalent of Task — a multiple of your resting burn. Sitting is 1 MET; a 6-MET activity costs six times as much energy per minute. It's how exercise researchers compare a swim to a bike ride without measuring everyone individually.
A deficit is eating below your total, so your body makes up the difference from its own stores and you lose weight. A surplus is eating above it, giving your body spare material to build with — and to store.
Short for macronutrients: protein, fat and carbohydrate, the three things in food that carry calories. Protein and carbs run about 4 calories a gram, fat about 9. Alcohol has 7 and belongs to no useful category.
The two equations doing the work here. Mifflin-St Jeor estimates your resting burn from age, height, weight and sex, and is the one most researchers reach for.
Katch-McArdle uses your muscle mass instead, so it needs a real body fat measurement. Given one, this site uses it — it's more accurate at the extremes, for very lean or very heavy bodies.
Eating at your total, so weight stays put. Worth knowing even if you're not aiming for it — it's the number you come back to after a diet, and the thing you eventually have to be able to live on.
Every number this site produces comes from one of the following. Where the research disagrees with the convention, that's noted.