Private Weight Tracker Apps for iPhone: How to Judge Them

A private weight tracker keeps your weigh-ins and photos away from anyone who doesn't need them, and that matters more than it first appears. A few months of numbers can hint at a pregnancy, an illness, a new medication or a hard stretch of life. Progress photos are more personal still.

The hard part is telling which apps deliver. "Private" shows up in plenty of App Store descriptions, and it can mean anything from "nothing leaves your phone" to "we don't sell your data, but it lives on our servers". This guide shows you how to check for yourself, then applies the checks to the apps people most often compare.

Since Periscope is one of the apps below, you should know we make it. It's a free weight tracker for iPhone. We researched every app, ours included, from its App Store listing and official website or privacy policy in October 2026. We haven't used each app for weeks, so where a listing or policy is silent we've written "Not stated" rather than guess.

Why is weight data sensitive?

Weight, body measurements and body photos are health information, but in the US the law people tend to assume covers them, HIPAA, generally doesn't. The FTC notes that many companies that collect health information, including diet and fitness app makers, fall outside it. What protects you is mostly the app's design and its promises.

Those promises have been broken before. In 2021 the FTC settled with the maker of the Flo period-tracking app, alleging it passed sensitive health information, including the fact of a user's pregnancy, to analytics and marketing companies after promising to keep it private. It wasn't a weight app, but the mechanism is generic: health events sent through ordinary analytics tools.

Photos raise the stakes. A weight is a number; a photo of you in underwear is a photo of you in underwear. If an app uploads it, you're trusting that company's storage, staff access and breach handling for as long as the file exists.

What can the App Store tell you?

Every listing has an "App Privacy" section, filled in by the developer. It's a quick first look, but Apple's guidance leaves gaps: data processed only on your device doesn't have to be listed at all, and every listing notes Apple hasn't verified the details. So an app can hold your weight, photos and Apple Health data and list nothing, and a short list doesn't prove much either way.

The privacy policy answers the questions that matter more: where your data is stored, whether you need an account, and which analytics tools the app uses. The rest of this guide works through those.

Where does a weight tracker store your data?

There are three common setups, and they differ a lot in who can get at your data.

The middle row has a catch. Apple's iCloud data security overview says Health data is end-to-end encrypted, but iCloud Backup and Photos are only end-to-end encrypted with Advanced Data Protection turned on. The app developer usually can't read app data stored in your iCloud, though.

Developer cloud storage isn't a red flag by itself. It's what makes multi-device sync, web access and coaching possible. It does mean trusting another company's security, and your data outlives the app on your phone until you delete your account.

Does needing an account matter for privacy?

An account means the developer holds at least your email or Apple ID, and probably your name. That's not much data, but everything else can hang on it: usage analytics, crash reports and support tickets can all be tied to a real person.

No account usually means the app can't identify you at all, which is why the strictest apps skip sign-up entirely. If you do need one, Sign in with Apple is the gentler kind, because Apple lets you hide your real email address from the developer.

What about analytics?

Most apps send some analytics: which screens you open, how long sessions last, when the app crashes. What matters is what goes into it and whether it's tied to you.

The privacy policy is where analytics companies get named. Noyoyo's policy names Google Analytics, Firebase and Mixpanel. Happy Scale's policy describes anonymous analytics sent to its own server and says no health data is included. Neither is wrong; they're different levels of exposure.

Do Face ID locks and export matter?

A lock protects you from people holding your unlocked phone: a partner, a kid, a colleague looking something up. It does nothing about servers, but for many people it's the more realistic risk. Weight Diary, Monitor Your Weight (PIN) and Periscope all list one.

Export is about control. If you can get your data out as a file, you can leave without losing years of history. Weigh In has CSV import and export, and Weight Diary has backup, import and export.

How we compared

We checked each app against five questions, using its App Store listing and official site or privacy policy as of October 2026:

1. Storage: device, your iCloud or the developer's servers.
2. Account: required, optional or none.
3. Analytics: what the policy says is sent, and which tools it names.
4. Lock: Face ID, Touch ID or passcode inside the app.
5. Export: whether you can take your data with you.

We didn't inspect network traffic or audit anyone's code, ours included. Prices are US App Store prices as of October 2026.

Which weight tracker apps are the most private?

Weigh In: nothing leaves the phone

Weigh In's privacy policy is as short as these get: everything you enter "is stored on your device and is not transmitted anywhere." There's no account, and it's free with no in-app purchases. You still get CSV import and export, reminders, a target weight and graphs.

What you give up is everything beyond weight. No photos, and no smoothed trend, predictions or widgets mentioned. The developer's site lists iCloud sync as coming soon, so for now your history lives on one device plus whatever your phone's own backup holds.

Weight Diary: the strictest app with a trend line

Weight Diary pairs on-device storage with a real trend line, a time-to-target estimate, a Face ID lock, Withings and Fitbit scale sync, and backup and export. Its policy says weight data stays on your device or in your Apple iCloud backup. It costs $7.99 once and needs iOS 18.

Watch the name: the free Weight Diary Lite is a separate listing with its own, looser privacy setup.

CompareMyself: photos that never leave the phone

CompareMyself keeps progress photos on the device with no account. Its policy says photos are stored only on your device and never uploaded. You log photos and weight, compare side by side and browse a timeline, free. It hasn't been updated since June 2025 and has no ratings yet, so treat it as a lightweight option rather than a full tracker.

Fitness Trackr, Happy Scale and Progress: close behind

Fitness Trackr keeps everything on the device, needs no account, and its policy says it doesn't collect analytics. It was released in July 2026 and has no ratings yet.

Happy Scale stores data on your device by default with optional Dropbox, and its policy says its anonymous analytics never include health data. It's the most established tracker of the group.

Progress keeps measurements and photos on your device and in your own iCloud. Photos are a Pro feature.

How private is Periscope?

Weights, photos, notes and any weights synced from Apple Health are stored on your iPhone. Our server stores only your account details: email or Apple ID, and name. Deleting your account removes those details and wipes the data on your phone. An optional Face ID lock covers the app.

Two things to know: you sign in with Apple before you start, and we use basic app analytics that never include your weight, photos or body measurements. There's also no data export or sync between devices.

In return you get the fullest free feature set among the on-device apps here: up to two progress photos per weigh-in, a before/after slider with a Play animation, a smoothed trend line in weekly, monthly and yearly reports, Home Screen and Lock Screen widgets (iOS 17 and later), and Apple Health sync, so smart-scale weigh-ins arrive on their own. No ads, subscription or in-app purchases.

Where do other apps beat Periscope on privacy?

• Account: Weigh In, Weight Diary, CompareMyself and Fitness Trackr work without signing up, and Happy Scale and Progress don't mention an account. Periscope uses Sign in with Apple.
• Export: Weigh In and Weight Diary let you take your data with you. Periscope doesn't.
• Backup: Progress and Weight Diary use your own iCloud, and Happy Scale offers Dropbox. Periscope has no sync or backup of its own, so treat its data as living on that one phone.

Our verdict

If you want nothing about you on anyone's server, choose Weigh In for weight only, Weight Diary if you want a trend line and will pay $7.99 once, or CompareMyself for photos. They are stricter than Periscope, and we'd say so to a friend.

For most people, though, privacy is one requirement among several. If you want your weigh-ins and photos kept on your iPhone and also want a smoothed trend, a before/after slider and widgets without paying, Periscope is our pick, as long as you're comfortable with Sign in with Apple. If you need multi-device sync or food tracking, you'll trade some privacy for it; MacroFactor is a good account-based choice.

• Nothing leaves the phone, weight only: Weigh In.
• Nothing leaves the phone, plus a trend line, paying once: Weight Diary.
• Nothing leaves the phone, plus photos: CompareMyself.
• No account, photos and trend charts, paying once: Fitness Trackr.
• On-device weights and photos, a smoothed trend, widgets and Apple Health sync, free: Periscope.

Whatever you choose, Apple Health makes a reasonable hub. Apple's Health page says Health data is encrypted on your device and, with two-factor authentication, end-to-end encrypted in iCloud. Give each tracker access only to the data types it needs; our guide to smart scales and Apple Health covers permissions. For features beyond privacy, see the best weight tracking apps for iPhone.

Tracking weight or taking body photos doesn't help everyone. If it feeds anxiety, or you have a history of disordered eating, it's fine to stop. The National Eating Disorders Association and, in the UK, Beat offer support.

Sources

1. Apple: App privacy details on the App Store (developer guidance)
2. Apple Support: iCloud data security overview
3. Apple: Health privacy
4. FTC: Flo Health settlement, January 2021
5. Weigh In on the App Store and privacy policy
6. Weight Diary on the App Store, Weight Diary Lite and privacy policy
7. CompareMyself on the App Store and privacy policy
8. Fitness Trackr on the App Store and website
9. Happy Scale on the App Store and privacy policy
10. Progress (Body Measurements Tracker App) on the App Store
11. Monitor Your Weight on the App Store
12. Periscope on the App Store
13. MacroFactor on the App Store
14. Noyoyo privacy policy
15. Lose It! on the App Store and MyFitnessPal on the App Store
16. FTC: Complying with the Health Breach Notification Rule
17. Apple Support: Manage apps that use Sign in with Apple