KMP vs CMP: Kotlin Multiplatform vs Compose Multiplatform – A Complete Guide

Introduction

As mobile and cross-platform development continues to evolve, Kotlin Multiplatform (KMP) and Compose Multiplatform (CMP) have emerged as two powerful technologies backed by JetBrains. While they are often mentioned together, they serve different purposes and solve different problems. This blog post explains what KMP and CMP are, how they differ, where they overlap, and when to use each.

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What is Kotlin Multiplatform (KMP)?

Kotlin Multiplatform (KMP) is a technology that allows developers to share business logic across multiple platforms while still writing platform-specific UI.

Supported Platforms

• Android (JVM)
• iOS (Native)
• Web (JavaScript)
• Desktop (JVM)
• Backend (JVM)

What You Share in KMP

• Business logic
• Data models
• Networking layer
• Validation logic
• Domain layer

What You Don’t Share

• UI code (by default)
• Platform-specific APIs

How KMP Works

KMP lets you write common code in a shared module (commonMain) and platform-specific implementations in:

• androidMain
• iosMain
• jsMain
• desktopMain

The shared code is compiled to native binaries or bytecode depending on the platform.

Key Benefits of KMP

• Maximum code reuse without sacrificing native UI
• Native performance
• Full access to platform APIs
• Easier gradual adoption in existing apps

KMP Example (Shared Logic)

class UserRepository {
    fun getUserName(): String {
        return "Saidur Rahman"
    }
}

Used from Android (Kotlin) and iOS (Swift) seamlessly.

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What is Compose Multiplatform (CMP)?

Compose Multiplatform (CMP) is a UI framework that allows developers to share UI code across multiple platforms using Jetpack Compose.

CMP focuses on how the app looks, not how business logic is structured.

Supported Platforms

• Android
• Desktop (Windows, macOS, Linux)
• Web (Experimental)
• iOS (Beta)

What You Share in CMP

• UI components
• Screens
• Navigation logic
• UI state management

How CMP Works

CMP uses the Compose declarative UI paradigm, where UI is written once and rendered across platforms.

CMP Example (Shared UI)

@Composable
fun Greeting(name: String) {
    Text("Hello, $name")
}

The same UI code can run on Android, Desktop, and iOS.

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Key Differences: KMP vs CMP

Feature	Kotlin Multiplatform (KMP)	Compose Multiplatform (CMP)
Primary Purpose	Share business logic	Share UI code
Focus	Data, domain, networking	UI and presentation
UI Sharing	❌ Not included	✅ Yes
Platform Access	Full native access	Limited in some cases
Maturity	Stable	Android stable, others evolving
Ideal For	Native apps with shared logic	Apps with shared UI

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KMP + CMP: Better Together

KMP and CMP are not competitors—they are complementary.

Ideal Architecture

• KMP → Shared business logic
• CMP → Shared UI layer

This approach enables:

• Maximum code sharing
• Faster development
• Consistent UI across platforms

Example Architecture

┌──────────────────────┐
│   Compose UI (CMP)   │
└──────────────────────┘
            ↓
┌──────────────────────┐
│ Shared Logic (KMP)   │
└──────────────────────┘
            ↓
┌──────────┬──────────┐
│ Android  │   iOS    │
└──────────┴──────────┘

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When to Use KMP

Choose Kotlin Multiplatform if:

• You already have native Android and iOS apps
• You want to share business logic only
• You need full control over native UI
• You want gradual migration

Common Use Cases

• Banking apps
• Enterprise apps
• Apps with complex business rules

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When to Use CMP

Choose Compose Multiplatform if:

• You want to build UI once and reuse it
• Your app UI is mostly similar across platforms
• You are starting a new project

Common Use Cases

• Internal tools
• MVPs and startups
• Desktop-first applications

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Performance Considerations

• KMP delivers native performance because it compiles directly to platform-specific binaries
• CMP performance is excellent on Android and Desktop, with iOS and Web still improving

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Learning Curve

• KMP is easier for existing Android developers
• CMP requires understanding Compose and declarative UI principles

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Final Verdict

Scenario	Recommended Choice
Share business logic only	KMP
Share UI only	CMP
Full cross-platform app	KMP + CMP

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Conclusion

Kotlin Multiplatform and Compose Multiplatform are shaping the future of cross-platform development. KMP excels at logic sharing, while CMP shines in UI sharing. Together, they provide a powerful, modern alternative to traditional cross-platform frameworks.

If you are an Android developer aiming to become a full-stack mobile engineer, learning KMP first and then CMP is a smart, future-proof strategy.