- KMP shares business logic; each platform keeps its own native UI layer
- Flutter shares everything through one engine: UI, logic, and rendering
- KMP is the safer bet for existing native apps adding incremental code sharing
- Flutter is faster for greenfield projects where one team owns the whole stack
- Netflix, McDonald's, and Cash App use KMP; Google Pay and BMW ship Flutter
KMP and Flutter both cut multi-platform costs, but they draw the line in different places. Flutter replaces the native UI layer with its own rendering engine. KMP shares business logic and leaves the UI native on each platform.
Where you draw that line shapes adoption, team structure, and how the app feels. KMP reached stable in late 2023. Compose Multiplatform for iOS moved to beta in 2024.
Key Differences
Architecture and What Gets Shared
KMP shares compiled Kotlin code for business logic: networking, database access, serialization, state management. The UI stays native: SwiftUI on iOS, Jetpack Compose on Android. The app looks and behaves native because the UI layer is native.
Flutter shares everything. UI, logic, and navigation are all Dart, rendered by Flutter's engine. One codebase, one team, but the UI is Flutter's version of platform conventions.
Compose Multiplatform blurs this line. As of v1.8.0 (May 2025), Compose Multiplatform for iOS is stable. Swift Export is the default in Kotlin 2.2.20, so shared code generates clean Swift interfaces. But shared UI is opt-in. Most KMP teams in production still write platform-specific UI.
Adoption Path and Migration
KMP's biggest advantage is incremental adoption. Share a single module (a networking layer or data model) without rewriting your app. Netflix, Cash App, Philips, and McDonald's (6.5M+ monthly purchases, 80%+ code sharing) all adopted KMP this way.
Flutter is all-or-nothing for most teams. You can embed Flutter in an existing native app, but the common path is a full rewrite. KMP wins for established apps. Flutter wins for greenfield projects.
Performance Characteristics
KMP compiles to native code on each platform: JVM bytecode on Android, native binary via Kotlin/Native on iOS. Shared logic runs at native speed with zero runtime overhead. The UI is native, so rendering performance matches a pure Swift or Kotlin app.
Flutter's Impeller engine delivers smooth 60fps for most UIs. It adds overhead native doesn't have: the Dart VM, the rendering pipeline, the layout system. For typical business apps, the difference is invisible. For complex, interactive UIs, KMP with native UI has an edge because nothing sits between your code and the platform renderer.
Developer Experience
Flutter is faster for daily work. Sub-second hot reload, real-time widget inspection, one language for everything. Building a screen is fast.
KMP requires two UI codebases (SwiftUI and Compose) and switching between IDEs. Development is slower, but the resulting app is indistinguishable from native.
Kotlin is more capable than Dart: coroutines, sealed classes, inline functions, a mature standard library. If your team knows Kotlin or Java, KMP feels natural. Dart is simpler but less expressive.
Ecosystem and Library Support
Flutter's pub.dev has over 40,000 packages. Google maintains official plugins for camera, maps, and payments. The ecosystem is mature.
KMP's library ecosystem is smaller but growing: Ktor for networking, SQLDelight for databases, Koin for DI, kotlinx.serialization. All production-ready. Because KMP shares logic (not UI), you also access each platform's native library ecosystem for UI work.
When Kotlin Multiplatform Makes Sense
Use KMP when native UI fidelity matters and you want to adopt cross-platform code one module at a time.
- You have existing native apps and want to share logic without rewriting
- Your team has strong Kotlin and Swift developers who want native UI
- Platform look-and-feel is critical (banking, health, enterprise)
- You want to start small with a shared networking or data layer
- Your Android team already uses Kotlin and can lead shared module work
When Flutter Makes Sense
Use Flutter when you want maximum code sharing and your product has its own visual identity.
- You are building a greenfield app and want one codebase from day one
- Your app has a custom, branded UI that doesn't need to match platform conventions
- Development speed is the top priority and you want one team writing everything
- You want to target web and desktop in addition to mobile
- Your team is comfortable learning Dart or already has Flutter experience
The Bottom Line
These two aren't competing. KMP is for teams that want native UI and gradual adoption. Flutter is for teams that want one codebase and are willing to own their rendering stack. The question: do you see the UI as something the platform provides or something you build?
Large companies with existing native apps lean toward KMP. Startups building from scratch lean toward Flutter. Both work in production. Pick based on your team and your app.