Apple Health Weight Tracking: Smart Scales, Sync and Trends

Apple Health weight tracking works like a shared notebook on your iPhone. You, your apps and your smart scale can all write weigh-ins into it, and any app you allow can read them back. Almost every sync problem comes down to who is allowed to write and who is allowed to read.

Health keeps the raw numbers and shows them by week, month and year. It doesn't smooth out the daily bounce, which is why many people pair it with something that works out what trend weight is. If you just want to see your trend from numbers you already have, you can paste them into a free weight trend calculator.

How does weight get into Apple Health?

There are three routes: you type it in, an app saves it, or a smart scale's companion app saves it for you.

By hand. Open Health, tap Browse, then Body Measurements, then Weight, and tap Add Data. Apple's guide to managing Health data has you enter the date, time and value, then tap Done. If you use an ordinary scale and no other app, this is all you need.

From an app. Plenty of weight and fitness apps can save weigh-ins to Health. They have to ask first.

From a smart scale. This is where most confusion comes from. The scale sends your reading over Bluetooth or Wi-Fi to the manufacturer's app, and that app writes it to Health. If the app isn't allowed to write weight, or hasn't run since you stepped on the scale, nothing arrives.

How do you sync a smart scale to Apple Health?

Install the scale maker's app, pair the scale, and say yes when the app asks to write weight to Health. The big brands all work this way:

Skipped the permission prompt? In Health, tap your profile picture, then Apps under Privacy, pick the scale's app and turn on Weight. Apple notes you may also need to switch on Health sharing inside the scale's own app.

Two small habits save a lot of head-scratching. Open the scale's app now and then, since some only push readings to Health while they're running. And if someone else uses the same scale, make sure their weigh-ins aren't landing in your profile.

How do you check which apps can read or write your weight?

Open Health, tap your profile picture, and under Privacy tap Apps. Each app has its own page with separate switches for what it can read and what it can write.

Apple's HealthKit documentation describes authorization per data type, with reading and writing requested separately. So you can let a tracker read your weight without letting it write anything, or let a scale app write weight without reading anything else. You can change these at any time in Health or Settings.

To see which sources have actually written weight, go to Browse, Body Measurements, Weight, scroll down and tap Data Sources & Access.

Why does an app show no weight data from Health?

Usually it's missing read permission, and the app can't tell you so. Apple's documentation says an app "doesn't know whether someone granted or denied permission to read data". A denied app just sees nothing, which looks the same as an empty Health app.

The other common cause is newer. When you grant access, iOS can ask how much history to share: a recent window or your full history. If a tracker shows this month's weigh-ins but not last year's, you probably picked the shorter window. Change it in the app's page under Profile, Privacy, Apps.

Why is there no weight trend in Apple Health?

Health's Trends section isn't a running trend line for every metric. Apple's guide to viewing Health data says Health "can alert you to significant changes" in data like resting heart rate, steps and sleep, and shows trends under Summary only "if Health has detected trends". Apple doesn't publish how much weight data that needs, or whether weight is always included. So if you're seeing no weight trend, or it looks unavailable, there isn't a setting to flip.

What you can do:

• Open Browse, Body Measurements, Weight and switch between the week, month and year tabs to see the shape of your data.
• Weigh in regularly. Sparse data gives any trend method less to work with.
• Use a tracker that reads weight from Health and calculates a moving average. That's the gap most weight apps fill, and the comparison of Apple Health and a dedicated weight tracker goes through what each does.

If the day-to-day jumps are what's bugging you, here's why your weight jumps day to day.

Why do you see duplicate weigh-ins, and which one counts?

Duplicates happen when two sources record the same weigh-in. Health ranks sources, and the default order is:

1. Data you enter manually
2. Data from your iPhone, iPad and Apple Watch
3. Data from apps and Bluetooth devices

A newly added source goes above your existing apps and devices. In Apple's words, "if multiple sources contribute the same data type, the data source at the top will take priority over others."

To reorder, go to Weight, Data Sources & Access, tap Edit, then drag a source up or down. Tapping the checkmark next to a third-party source turns it off for weight.

To remove one bad reading, go to Weight, tap Show All Data, swipe left on it and tap Delete. If your Health data syncs over iCloud, Apple says deleting it on one device removes it from all your synced devices.

One catch: priority only affects Health's own display. A third-party app that reads weight may see every reading from every source and decides for itself what to do with two on the same day.

How do weight tracker apps use Apple Health?

A tracker asks to read weight (and sometimes to write it), then pulls readings into its own log. Beyond that, apps differ. Some only read when you open them, some write your manual entries back to Health, and some also ask for body fat or steps. The app's page under Profile, Privacy, Apps shows exactly what it requested.

Periscope, for example, asks only for weight. Turn on Apple Health sync and new weigh-ins, including your smart scale's, come in each time you open the app, without touching anything else in Health.

Sources

1. Apple Support. Manage Health data on your iPhone, iPad, or Apple Watch.
2. Apple Support. View your data in Health on iPhone.
3. Apple Developer Documentation. Authorizing access to health data.
4. App Store. Withings.
5. App Store. RENPHO Health.
6. App Store. EufyLife.