Body fat percentage by sight is a self-estimate: the app shows a row of silhouettes labelled with ranges and asks you to tap the one that looks most like you. What it records is a band, not a number, and it is used as context on your profile rather than as an input to your targets. This article explains why the question is asked, what the nine bands are, and — because it matters for how much weight to put on the answer — exactly what the estimate is and is not used for.
Why apps ask
Total mass tells a nutrition formula less than it would like to know. Two people of the same height and weight can carry very different amounts of fat and lean tissue, and some metabolism equations and protein rules are written per kilogram of lean mass rather than per kilogram of body weight. To use those, an app needs some idea of composition — and the cheapest way to get one is to ask.
Asking by picture rather than by number has a practical reason: most people do not know their body fat percentage, and the methods that would tell them (calipers, scans, impedance scales) are unavailable, expensive or unreliable at home. A silhouette question takes five seconds and produces an answer in the right neighbourhood, which for a wide band is all that is needed. MacroDiet's onboarding screen says exactly that: "Tap the image closest to you. A rough estimate is all we need."
The nine ranges
The screen offers nine bands, each with a silhouette for your selected sex:
| Band (stored value) | Label shown | Width |
|---|---|---|
3-4 | 3–4% | 2 points |
5-7 | 5–7% | 3 points |
8-12 | 8–12% | 5 points |
13-17 | 13–17% | 5 points |
18-23 | 18–23% | 6 points |
24-29 | 24–29% | 6 points |
30-34 | 30–34% | 5 points |
35-39 | 35–39% | 5 points |
40+ | 40%+ | open |
Three things about the list. The bands get wider in the middle, where most people fall and where a picture is least able to tell neighbours apart. The web calculator, which does not ask the question, fills in 18-23 for men and 24-29 for women as a neutral default. And the lowest bands exist to make the scale complete, not as a target: the screen has no "best" band and the app attaches no judgement to any of them.
The precision is what you would expect from looking at a drawing: the pick depends on lighting, posture, how recently you trained and how you see yourself on the day. Two people with the same measured composition can plausibly tap adjacent pictures. A band is the honest unit for that kind of estimate; a number to one decimal place would be false precision.
In plain terms: it is a rough, self-reported band, and it is stored as exactly that.
What the estimate is used for — and not
This is the part worth being precise about, because it decides how much the answer matters.
Used for: the band is saved on your profile and shown on the MacroDiet dashboard as context next to your other foundation answers. If you later log a scale body-fat reading (both MacroDiet and Zyra Workouts have an optional body-fat field next to weight), you can watch it over time in the same way as weight.
Not used for: the current calorie and macro formula. The arithmetic that sets your targets runs on other inputs:
| Target | What it is computed from | Body-fat band involved? |
|---|---|---|
| Calories (maintain) | Mifflin-St Jeor from sex, age, height, weight; × activity multiplier from sessions per week and daily movement | No |
| Calories (lose / gain) | Maintain ± weekly rate (a percentage of body weight) × 7,700 kcal/kg ÷ 7, with the floors and the 35% cap | No |
| Protein | Body weight × grams per kilogram from your protein preference, +0.2 g/kg in a deficit; capped at 50% of calories | No |
| Fat and carbohydrate | The remaining calories split by your diet style, with the fat floors | No |
The same is true of readings from a smart scale: MacroDiet's own in-app note says scale body-fat percentage does not influence its algorithms, but you can track it. So if you picked a band you now think was wrong, nothing about your targets needs to change; the protein calculator and the calorie calculator will give you the same numbers either way.
Two consequences follow. First, do not agonise over the pick; the nearest picture is enough. Second, if you want to see composition change, a tape measure — same site, same tension, compared over 30 or 90 days (how to take body measurements) — is far more repeatable than re-guessing a silhouette, and pairs with the trend weight to show what the scale alone cannot (why the scale doesn't match the mirror).
The short version
The body-fat question is a picture pick stored as one of nine bands from 3–4% to 40%+. It is a rough self-estimate, kept on your profile and shown as context; the current calorie and macro formula does not read it, and neither does a smart scale's body-fat number change any target. Pick the nearest silhouette and move on. For nutrition and training progress, the trend weight and a tape measure carry the information; the band is a description, not a verdict. Educational overview only — not medical advice.