How your calorie target is calculated (and why it keeps moving)

Every fat-loss app shows you a calorie number. Almost none of them tell you where it came from, which makes it very hard to trust on the day it feels too low.

Yours is built in three steps from the stats you entered, and each one is worth understanding — because when you know how the number is made, you stop negotiating with it.

Step one: your resting burn

The starting point is how much energy your body spends doing nothing at all — keeping you warm, breathing, thinking. It's the largest single share of your daily total, and it's estimated from four inputs: weight, height, age and sex.

That estimate is exactly what it says. Two people with identical stats can differ by a few hundred calories, which is why the program treats the first week as a calibration period and adjusts from what the scale actually does, rather than trusting the equation forever.

Step two: your activity multiplier

Resting burn gets multiplied to account for everything you do on top of it — training, steps, work, fidgeting. This is where most calculators go wrong, because people reliably overestimate how active they are.

The program deliberately errs low. An overestimated multiplier produces a generous target and a flat scale, which is the single most demoralising way for week two to go. A conservative one produces a target you'll actually see results from.

Step three: the deficit

Then a deficit is applied — a percentage cut rather than a flat number, so it scales with body size. A percentage-based cut means a 240 lb starter and a 150 lb starter both get a deficit that's aggressive relative to them, instead of one that's trivial for one and punishing for the other.

The floor matters as much as the size. Health agencies are consistent that very low intakes belong under medical supervision, so the program holds a sensible minimum regardless of what the arithmetic suggests.

• Deficit is a share of maintenance, not a fixed 500 calories for everybody
• Protein is protected first — the cut comes out of carbohydrate and fat
• There's a floor. The equation can't push you below it
• The target is a daily average, not a rule about any single meal

Why it moves

A smaller body costs less to run. Lose ten pounds and your resting burn falls, the energy cost of every step falls with it, and yesterday's deficit becomes today's maintenance. Left alone, that's exactly how a program stalls in week three while you're still doing everything right.

So the target re-computes from your latest weigh-ins. You'll see the number drift down as the month goes on. That isn't the app punishing you for progress — it's the only way the deficit stays the same size relative to the person actually eating it.

“A target that never changes stops being a deficit around the time you start deserving one.”

When to override it

• Don't eat below it on a whim — a bigger hole doesn't produce a faster result, it produces a shorter program
• Don't eat back your training. The multiplier already accounts for it
• If you've been under the target for four days and the weekly average hasn't moved, audit measurement before changing anything
• If you're dizzy, cold, or your training collapses, that's a signal to check intake and speak to a clinician — not to push harder