Your scale and Apple Health
Your scale talks to its own app, and that app writes to Apple Health. HealthAPI reads Apple Health, so the scale's app has to be allowed to write there first. What each brand says:
| Scale app | How to turn it on | Worth knowing |
|---|---|---|
| Withings | Turn on Apple Health in the Withings app. | Shares weight, body fat percentage, BMI and lean body mass. Accounts created on or after October 13, 2026 need Withings+ for it. |
| Renpho Health | In the Health app: your profile, Apps, Renpho Health, then turn on the categories. | Renpho doesn't list which measurements it writes, so check Weight in the Health app after a weigh-in. |
| EufyLife | In EufyLife, open Me and connect Apple Health. | Only the main user's measurements sync. Eufy suggests a separate account for each person. |
| Hume Health | In Hume Health: your profile, Connected Apps, Connect, then allow access. | Not every Hume metric has an Apple Health equivalent, and Hume's own scores stay in its app. |
To check: in the Health app, tap Browse and open Weight (or Body Fat Percentage), then scroll down to Data Sources & Access. Your scale's app should be listed.
What the AI reads
| Metric | API name | What the AI gets |
|---|---|---|
| Weight | bodyMass | Kilograms. Each weigh-in, and a daily average, low and high |
| Body fat | bodyFatPercentage | Percent, per reading and per day |
| Lean body mass | leanBodyMass | Kilograms, per reading and per day |
| BMI | bodyMassIndex | As your scale's app wrote it |
| Height | height | Meters |
Apple Health has no place for muscle mass, body water, bone mass or visceral fat, so those never leave your scale's app. One lookup returns up to 365 days of daily weight, or the single weigh-ins from up to 31 days. The same connection reads your steps, active energy and workouts from the rest of the 50 synced metrics, read only.
Set it up in 4 steps
Send your scale to Apple Health
Turn on Apple Health in your scale's app, as in the table above, and weigh in once.Install HealthAPI
Get it from the App Store and allow Weight, Body Fat Percentage and Lean Body Mass when it asks for Apple Health access.Ask about your weight
Start with “What's my weekly average weight trend?”, then try the prompts below.
Prompts that work
“Is my weight actually going down? Use pounds.”
Yes, slowly. Your 7-day average is 179.4 lb, down about 0.8 lb a week over the last 6 weeks. Single weigh-ins swing by up to 2.6 lb day to day, which hides it.
Where you are now
- “What are my latest weight, body fat and lean body mass, and when was each one measured? Use pounds.”
Weekly averages, not daily noise
- “Show my weekly average weight for the last 12 weeks, with the change from the week before.”
- “How much does my weight swing within a week? Give each week's lowest and highest weigh-in.”
Rate of change
- “Using 7-day averages, how fast has my weight changed per week over the last 8 weeks?”
- “Compare that rate for the last 4 weeks with the 4 weeks before.”
Body composition
- “Over the last 3 months, as my weight changed, what happened to my body fat percentage and lean body mass?”
Weight and activity
- “For each of the last 12 weeks, show my average weight, average daily steps, active energy and workout minutes.”
- “Do weeks with more workout minutes line up with a bigger drop in my weekly average weight?”
Checks before you trust an answer
- “Which days in the last 30 have no weigh-in?”
- “List each weigh-in from the last 2 weeks with its time of day.”
Getting better answers
- Ask for weekly averages. A 7-day average smooths out the day-to-day ups and downs, so it shows the trend a single number can't. Weighing in at the same time of day helps too.
- Missing days are missing, not zero. The AI averages the days you weighed in. Ask which days have no weigh-in when a week looks off.
- Watch for other people on your scale. A guest's weigh-in saved to your account lands in your Apple Health and pulls your average. Ask for each weigh-in with its time to spot one.
- One app per measurement. If your scale's app and another app both write weight, each weigh-in can show up twice. In the Health app, open your profile, then Apps, and turn off writing weight in the one you don't need.
- Read body fat as a trend. A home scale estimates body fat and lean mass, so the direction over weeks says more than any one reading.
- Patterns, not advice. HealthAPI and the AI apps aren't medical devices. For a change you didn't expect, or a goal you're unsure about, talk to a doctor.
Prefer a spreadsheet?
The Google Sheets guide adds a row of yesterday's numbers each morning with a short script, and weight can come from the API's trends endpoint. For Excel, see Apple Health in Excel. To bring your trend to an appointment, the doctor summary guide puts it on one page with your heart rate, blood pressure and sleep.
Questions
Does my Withings scale sync to Apple Health?
Withings lists weight, body fat percentage, BMI and lean body mass among the data it shares with Apple Health. Withings also says accounts created on or after October 13, 2026 need a Withings+ subscription to send data to Apple Health; accounts made before then aren't affected.
Does Hume Health sync to Apple Health?
Yes, from the Hume Health app: your profile, Connected Apps, then Connect, and allow access. Hume says not every Hume metric has an Apple Health equivalent, and its own scores stay in the Hume app. After a weigh-in, check Weight in the Health app to see what arrived.
Can I see my weight in pounds?
Yes, ask for pounds. HealthAPI reads weight in kilograms, as Apple Health stores it, and the AI converts it (1 kg is about 2.2 lb). Say it once at the start of the chat.
Why doesn't the AI see my muscle mass or body water?
Apple Health has places for weight, body fat percentage, lean body mass and BMI, but none for muscle mass, body water, bone mass or visceral fat, so those stay in your scale's own app.
How far back can the AI look?
As far back as your synced history goes: a year by default, or more with a longer Import History in HealthAPI's Sync Settings. One lookup covers up to 365 days of daily weight, so a year's trend takes one request.
Can the AI tell me what I should weigh?
No. It can show your trend and how it lines up with your activity, but HealthAPI and the AI apps aren't medical devices. For a goal weight or a change you didn't expect, talk to a doctor.
