How AtomFitness Calculates Your Nutrition Goals

AtomFitness sets your calorie and macro targets from a formula on day one, then replaces that guess with what your own data says. This guide is the arithmetic behind both, in plain language.

📖 Related: See the Goal Tracking Guide for setting a goal, weighing in and running a check-in.

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Energy Balance

Everything here rests on one number: 7,700 kcal per kilogram of body-weight change (3,500 kcal per pound). Eat below what you burn and the difference comes off; eat above it and it goes on.

Your TDEE — total daily energy expenditure — is what you burn in a day: your basal metabolic rate, plus movement and training, plus digesting food. A formula can estimate it. Only your own weight trend measured against your own intake can measure it, and that is what the weekly check-in does.

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Your First Targets

When you create a plan, AtomFitness works in four steps:

1. BMR from the Mifflin–St Jeor equation, using your sex, age, height and current weight.
2. TDEE = BMR × your activity multiplier (sedentary 1.20 · lightly active 1.375 · moderately active 1.55 · very active 1.725 · extra active 1.90).
3. Target calories = TDEE − your pace's deficit (losing), + your pace's surplus (gaining), or TDEE itself (maintaining).
4. The floor, if step 3 lands under it: 1,500 kcal/day for men, 1,200 for women. If the floor clips your target, the app tells you, and your timeline is stretched to match the deficit you are actually running.

Your pace's deficit or surplus is the single source of every rate in the app — the timeline, the check-in's idea of "on pace", and the target itself all come from the same table.

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Paces, in Two Units

One table, stated two ways. The calories per day are the stored number; the weekly rate is that number converted at 7,700 kcal/kg.

Maintain is 0.

The gain column is deliberately smaller than the loss column: lean tissue is laid down far less efficiently than fat is burned, so a bulk is run at the paces the app has always advertised — 0.28 / 0.17 / 0.08 kg per week — and those surpluses are exactly those paces converted. Because the plan and the check-in read the same table, a check-in that finds you moving at your advertised pace changes nothing at all.

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Macros

Once the calorie target is set, it is split the same way at plan creation and at every check-in:

Protein is 1.8 g/kg when the plan is created and 1.8 g/kg at every check-in afterwards, so re-splitting an unchanged calorie target can never hand you different grams than the plan was built with.

If you set your own targets in the targets sheet, the three ready-made programs use: Balanced 1.8 g/kg protein and 25% fat, High protein 2.4 g/kg, Low carb 2.0 g/kg with 45% fat.

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The Weekly Check-In

A check-in reads the seven completed days before today and your recent weigh-ins, and runs the same rules in the same order every time.

What it needs before it will run

Five of seven logged days is enough because the missing days are filled in from your logged average (with a small 4% correction at exactly five days, which is where under-logging tends to bite). Fewer than five and it falls back to weight only — or, if it cannot do that either, it does nothing and tells you what is missing.

You have a 2-day grace period on your check-in day, and a check-in run fewer than 5 days after the last one is refused rather than applied twice.

What it does

1. Smooths your weight. It averages your weigh-ins into weekly buckets and fits a line through the last four weeks, so the number it works from is a trend, not Tuesday.
2. Measures your TDEE. Your average intake minus your weekly change converted at 7,700 kcal/kg. Losing weight puts your measured TDEE above what you ate.
3. Clamps what it learned. The new TDEE can sit at most ±250 kcal/day from the estimate it held before, so one strange week cannot rewrite your metabolism.
4. Applies the BMR floor. A measured TDEE below your own BMR is not believable; it is raised to your BMR.
5. Computes the ideal target — measured TDEE minus (or plus) your pace's number from the table above.
6. Dampens the move by confidence (below), then applies the guards.
7. Clamps the change to ±250 kcal/day for this check-in, then applies the calorie floor.

So a single check-in can move your calories by at most 250 kcal a day, and can never take them under 1,500 (men) or 1,200 (women).

The guards

Three rules can stop a change the arithmetic would otherwise make:

• Water weight. If the week's intake predicted one direction and the scale went the other, and you have fewer than three weeks of buckets, the week is treated as contradicted: confidence drops a level and the app refuses to move in the direction that week is pushing.
• Already past your pace. If you are losing faster than your plan intends, it will not cut further; if you are gaining faster than the plan intends, it will not add more.
• Maintenance. When you are maintaining, it never feeds a drift — gaining, it will not add calories; losing, it will not remove them — and any change is capped at ±150 kcal/day.

You may also see a note rather than a change: a plateau (under 0.23 kg/week across three or more weekly buckets), an outlier (more than 2.27 kg between two consecutive weigh-ins), or an extreme week (more than 1.36 kg/week, which costs a confidence level).

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Confidence

Every check-in scores how much it should trust this week's data, out of 100:

A single weigh-in in either of the two weeks costs 10 points — one scale reading is not a trend.

An extreme weekly change, or a contradicted week, drops you one level. So an ideal change of +300 kcal applies as +300 at high confidence, +180 at medium and +90 at low — before the ±250 clamp and the floor.

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Safety Limits

The floors are applied at plan creation as well as at check-in, so a plan can never be created below a floor the check-in would then refuse to go under.

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When It Uses Weight Only

If you have weigh-ins but not enough logged food, the app falls back to your weight trend alone. It needs weigh-ins in at least 3 of the last 4 weeks, spanning at least 7 days, and it closes the gap between your observed rate and your plan's rate rather than measuring a TDEE it has no intake for.

Confidence on this path is capped at medium, so the change it makes is always a fraction of the ideal one. With neither five logged days nor three weeks of weigh-ins, the check-in makes no change and tells you which one is missing.

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Dynamic Mode

Dynamic Mode (daily adaptive calories) adds the energy Apple Health says you actually burned today on top of your target, for today only.

• It reads active energy from Apple Health, from midnight to now, on iPhone. It needs a health connection; a day reading over 8,000 kcal is treated as bad data and ignored.
• The bonus is capped at half your base calorie target, and on a losing plan also at your plan's daily deficit — so a big training day can give back the deficit, but never more than it.
• The bonus is split across protein, carbs and fat in the same proportions your targets already use, and Today, Meals and Goals all show the same adjusted number.
• Your stored target does not change. Dynamic Mode is a display-time addition; turning it on or off recalculates nothing.
• At your check-in, the app subtracts the week's mean daily active energy before setting the new target, because the TDEE it just measured already contains the training you ate for. It needs at least 4 usable days out of 7 to have a mean at all.

The Energy card on Today is a different number: it shows what you burned (your measured expenditure plus today's active energy) rather than what you may eat. Expenditure is never capped; only the target is.

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Why Tracking Accuracy Matters

Critical rule: only log a day you can be reasonably accurate about. It is better to skip a day than to log a wrong one.

The check-in measures your TDEE from what you logged. So:

• Under-logging makes your measured TDEE too low, which sets your calories too low.
• Over-logging makes it too high, which stalls your progress.
• Logging only your good days does the same thing as under-logging.

Missing data the app can handle — fewer than five logged days simply moves it to the weight-only path, which is less precise but unbiased. Systematically wrong data it cannot detect at all. When in doubt, leave it out.

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Frequently Asked Questions

Why didn't my calories change after a check-in?

The most common answer is that you are on pace: your plan's surplus or deficit and the check-in's idea of "ideal" come from the same table, so moving at the advertised rate produces a change of zero. Otherwise: confidence was low and the change was damped, a guard stopped it, or you are sitting on the calorie floor.

Why did my calories go up during a cut?

Because the app measured your TDEE higher than it had assumed, and your pace's deficit is taken from the measured number. That is the system learning your metabolism, not abandoning the goal.

Why can't I check in yet?

A check-in needs at least 5 days since the last one. You also have a 2-day grace period on your check-in day, so a day late is fine.

My weight jumped 2 kg this week — should I worry?

Short-term swings come from water, sodium, carbohydrate, the menstrual cycle, digestion and training inflammation. The check-in fits a line through four weeks of weekly averages precisely so one week cannot drag your targets around, and a week whose scale contradicts your log is flagged as water weight and damped further.

Does the app need Apple Health?

No. Targets, check-ins and Today all work from what you log. Apple Health is only required for Dynamic Mode, which adds today's measured activity on top of your target.

Can I set my own targets instead?

Yes — the targets sheet lets you take the plan's numbers or set your own, with Balanced, High protein, Low carb and Custom programs. Custom calorie targets are accepted between 500 and 15,000 kcal/day.

How long before the numbers are trustworthy?

The first check-in that has five logged days and weigh-ins in both weeks already measures something real. Confidence climbs as you add logged days and weigh-ins, and the four-week regression means three to four weeks of consistent data is when the trend line, rather than the formula, is doing the work.

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The Bottom Line

• Day one is a formula: Mifflin–St Jeor, your activity multiplier, and your pace's number.
• Every check-in after that measures your TDEE from what you ate and what the scale did, and moves your target toward it — by at most 250 kcal a day, damped by how good the week's data was, and never below the floor.
• Protein is 1.8 g/kg throughout, fat is 25% of calories, carbohydrates take the rest.
• The more days you log and the more often you weigh in, the more of the change the app is willing to make.