The method
How ArcBody works out your numbers.
Where your targets come from, when they change, and how far to trust each food number.
Starting targets
Your first targets, step by step.
Worked out once from your profile when you finish setting up. You can type your own numbers at any time.
Resting energy
What your body burns at rest, from the Mifflin-St Jeor equation, with weight in kilograms, height in centimetres and age in years.
then + 5 for men, or − 161 for women
Daily activity
Resting energy times a factor for how active your days are, outside of workouts. Workouts and steps are not added on top.
On my feet sometimes × 1.375
Regularly active × 1.55
Physical job or daily exercise × 1.725
Hard training most days × 1.9
Your pace
Each kilogram you want to lose or gain counts as 7,700 kcal. Spread over a week, that is 1,100 kcal a day for every kilogram a week. The default pace is 0.4 kg a week to lose fat and 0.25 kg a week to build muscle.
Limits on the pace
A pace that is too fast is eased: losing at most 1% of your body weight a week, gaining at most 0.5%. A deficit never goes beyond 30% of what you burn, and with a BMI under 18.5 ArcBody offers no deficit at all.
Floors
The target never goes below 1,200 kcal for women or 1,500 kcal for men, or below 80% of your resting energy, whichever is higher.
Protein, fat and carbohydrate
Protein follows the level you pick at setup: Low 1.6 g, Moderate 1.8 g, High 2.2 g or Extra high 2.5 g for every kilogram you weigh today. Moderate is the default. Tick Use my goal weight and protein is counted on the weight you are aiming for instead, which keeps it sensible if you have a lot to lose. Fat is a quarter of your calories. Carbohydrate takes the calories left. Protein and carbohydrate have 4 kcal a gram, fat has 9.
Fat calories × 25% ÷ 9
Carbs calories left ÷ 4
One worked example
A woman of 35, 165 cm and 70 kg, on her feet sometimes, losing at the default pace, with Moderate protein.
- Resting energy
- 1,395 kcal
- Times 1.375 for her activity
- 1,918 kcal
- Losing 0.4 kg a week
- −440 kcal
- Daily target
- 1,478 kcal
- Protein, Moderate, 1.8 g × 70 kg
- 126 g
- Fat, a quarter of the calories
- 41 g
- Carbohydrate, the rest
- 151 g
Weekly check
What the weekly check does.
It compares what you ate with what the scale did, then proposes a change. Nothing changes until you tap Apply.
Enough data first
It reads the last 14 days and needs at least eight logged days and five weigh-ins. A day below 80% of your resting energy counts as not fully logged and is left out.
Your real burn
Your weight change comes from the middle value of the slopes between every pair of weigh-ins, so one odd morning barely moves it. Your burn is your average daily intake, corrected by that change, and it is kept between one and two and a half times your resting energy.
The proposal
Your burn plus your pace, the same way as at the start, rounded to the nearest 10 kcal.
When it lowers a target
Only when your weigh-ins show you losing more slowly than your plan, by more than 0.1 kg a week. On pace, your target stays.
Step and floor
One change moves the target 300 kcal at most and never below 1,200 kcal for women or 1,500 kcal for men. A change under 25 kcal is not shown at all.
Fast changes
If your weight moves more than 1.5 kg a week, or you lose more than 1.5% of your body weight a week, it shows no new numbers, leaves your targets as they are and suggests a doctor or dietitian.
You decide
Tap Apply new targets or Keep current. Either way, it waits seven days before it checks again.
One worked check
Two weeks later the same woman has logged about 1,500 kcal a day, and her weigh-ins show 0.2 kg lost a week instead of 0.4.
- Average intake
- 1,500 kcal
- Losing 0.2 kg a week adds back
- +220 kcal
- Her real burn
- 1,720 kcal
- Losing 0.4 kg a week
- −440 kcal
- Proposed target
- 1,280 kcal
- Change from 1,478 kcal, inside the 300 limit
- −198 kcal
Weight trend
Why the line moves slowly.
Daily weight swings with water and food. The trend line moves a tenth of the way towards each weigh-in.
The smoothing
Each new weigh-in pulls the trend 10% of the way towards it. Two weigh-ins on the same day are averaged first.
Gaps
Days without a weigh-in carry the trend forward. After more than 10 days without one, the trend starts again from your next weigh-in.
Weekly change
Today's trend minus the trend a week ago. It appears once there is a full week of trend to compare.
Food data
Where each food number comes from.
Four sources, each checked in its own way, and a way to flag anything that looks wrong.
Everyday foods
Built into the app: foods from USDA FoodData Central (its SR Legacy and Foundation releases), plus foods written by hand for what those lists miss. Names are kept short, baby food and restaurant categories are left out, and every food needs protein, carbohydrate and fat values. Values are per 100 g.
Restaurant menus
Every dish is compared with the chain's own published nutrition figures and must match to within 10 kcal, 1 g of each macro and 20 mg of sodium. The first full check, on 30 September 2026, went through every dish: any that did not match was corrected, and dishes a chain no longer sells were removed. KFC and Pizza Hut publish their figures through Nutritionix, and Dairy Queen's were read from archived copies of its own pages.
Packaged products
Looked up on Open Food Facts, a free database run by volunteers, when you search or scan a barcode. ArcBody does not check these entries, and search labels them Open Food Facts so you can tell. A product you open or scan is saved on your phone, so the next scan works offline.
Label scanning
The camera reads 11 fields from a nutrition label. A number counts only when two camera frames agree on it, the calories must roughly match the macros, and you review every number before it's saved.
Reports
Every food has Report wrong data. The report holds the food, the problem you picked and your note, plus a random install number and the app version. Reports are read by hand, and corrections ship in an app release.
Updates
A new release refreshes the built-in foods and leaves your favourites, recent foods and your own foods alone. Past diary days keep the numbers they were logged with.
Limits
Where these numbers can be wrong.
Every calorie, macro and expenditure figure is an estimate. These are the gaps we know about.
The equation is an average
Mifflin-St Jeor describes a typical person of your size and age. Your body can burn more or less, which is why the weekly check exists.
Missed logging
The weekly check trusts what you log. A forgotten snack makes your burn look lower than it really is.
Water on the scale
Water moves the scale from day to day. The trend line softens that, and the weekly check waits for two weeks of weigh-ins for the same reason.
Restaurant kitchens
A dish made in a busy kitchen will not match its published figure exactly. US chains also show US figures to people in Canada.
Volunteer data
Open Food Facts entries are typed in by volunteers and can be wrong. Check them against the label, or scan the label instead.
Not medical advice
ArcBody is a tracking tool for adults. It does not diagnose or treat anything. If you are pregnant, have a medical condition or a history of disordered eating, talk to a doctor before following any calorie target.
See it work on your own numbers.
Join the waitlist for the launch message, and tick the box if you would like to test it first.
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