Short answer

HealthKit (iOS) is mature, well-documented, and the libraries just work. Google Fit (Android) is in a long deprecation transition to Health Connect. If you are starting today, you wire HealthKit on iOS and Health Connect on Android — not Google Fit.

I learned this the hard way shipping a fitness app in March 2026.

HealthKit on React Native

What works

• react-native-health covers most read APIs (steps, heart rate, workouts, sleep, weight).
• Permissions flow follows Apple''s pattern — single sheet, granular per data type.
• Background updates via observers and enableBackgroundDelivery.
• Apple''s privacy enforcement is strict but predictable.

What hurts

• iOS-only. Pretending it solves Android too is the trap.
• Apple Watch data requires extra entitlements and an actual Watch app for some data types.
• The NSHealthShareUsageDescription and NSHealthUpdateUsageDescription strings must be specific or App Review will reject.

Time to first working read

• HealthKit (steps + heart rate): about 3 hours, including App Store privacy declarations.

Google Fit / Health Connect on React Native

The transition

Google deprecated the Google Fit API. Android 14+ uses Health Connect as the unified store. New apps should target Health Connect. Old Google Fit code still works on older devices but is on borrowed time.

What works

• react-native-health-connect is the active library to target.
• Conceptually similar to HealthKit — permission grants per data type, async reads.
• Once permissions are granted, reads are reliable.

What hurts

• Documentation is thinner than HealthKit''s. Stack Overflow will not save you.
• Health Connect is opt-in for many users — if they have not installed/enabled it, your reads return empty.
• Permission UI varies by Android version. Test on at least Android 13 and 14.
• Background reads are more constrained than HealthKit''s observer pattern.

Time to first working read

• Health Connect (steps + heart rate): about 3 days, mostly spent on permission UX and emulator setup.

What you actually need to ship a cross-platform fitness app

• HealthKit on iOS via react-native-health (or an Expo equivalent).
• Health Connect on Android via react-native-health-connect.
• A thin abstraction layer in your code so the rest of the app does not care which platform it is on.
• Privacy strings done right on iOS. App Review will sit on you otherwise.
• A clear UX flow when permissions are denied — both platforms hide the re-grant deep in settings.

My default

Build the iOS path first with HealthKit. Validate the product. Then port to Android with Health Connect. The reverse order will burn a week of runway on permission edge cases.

What Shippen ships

• The Expo + HealthKit stack guide
• The HealthKit React Native integration walkthrough
• Pre-wired permission flows in the boilerplate so you do not redo Apple''s privacy plumbing for every project
• Reusable patterns for both HealthKit and Health Connect inside one shared interface

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