---
title: "Swift on Android vs Kotlin Multiplatform: which one should share your code?"
description: "Swift 6.3 brought an official Swift SDK for Android. How it compares with Kotlin Multiplatform, and how to choose which one shares your app's code."
author: "MH TOUFIK"
published: 2026-11-07T03:00:00.000Z
updated: 2026-11-05T08:06:35.000Z
url: https://toufik.dev/blog/swift-on-android-vs-kotlin-multiplatform
category: "Cross-Platform"
tags: ["Android", "Compose Multiplatform", "Kotlin Multiplatform", "Swift", "iOS"]
---

# Swift on Android vs Kotlin Multiplatform: which one should share your code?

For years, sharing code between Android and iOS meant one serious option for native developers: **Kotlin Multiplatform (KMP)**. Write your logic once in Kotlin, use it from Swift on iOS.

In March 2026 the other side made its move. **Swift 6.3 shipped the first official Swift SDK for Android.** Now an iOS team can write shared logic in Swift and use it from an Android app.

So which one should you pick? I build with KMP myself (my **প্রশ্নব্যাংক** question bank app shares its core between Android and iPhone), so I'll try to be fair about both.

## What each one actually does

**Kotlin Multiplatform** lets you write shared code in Kotlin: models, networking, database and business rules. On Android it's just Kotlin. On iOS it compiles to a native framework that Swift can call. If you want, **Compose Multiplatform** lets you share UI too, and it's stable on iOS.

**The Swift SDK for Android** lets you compile Swift for Android. You build your Swift code into native libraries and call them from your Kotlin or Java app through **swift-java**, which handles the JNI plumbing for you. In Swift.org's words, you can "integrate Swift code into existing Android applications written in Kotlin/Java".

The key point: **the Swift SDK shares logic, not UI.** Your Android screens are still built with Android tools, like Jetpack Compose. There's no official SwiftUI for Android.

## How to choose

![Swift on Android or Kotlin Multiplatform?](https://toufik.dev/media/diagram-04-swift-or-kmp-v2-e088ecf4.webp "Pick the language your team is strongest in for shared logic; keep each platform's UI native, or share UI with Compose Multiplatform.")

The simplest question is: **where is your team strongest, and where does your existing code live?**

### Pick the Swift SDK for Android if…

- You have a **mature iOS app** with a lot of logic already in Swift.
- Your team is **mostly iOS developers**, and Android is the newer platform.
- You want to bring **specific Swift modules** (a parser, a sync engine, a calculation library) to Android, not rebuild your whole architecture.

Be ready for some rough edges. The SDK is officially released, but the tooling is young. Swift.org's getting-started guide covers command-line builds and points to examples for full apps; there's no one-click Android Studio template yet.

### Pick Kotlin Multiplatform if…

- You're **starting fresh**, or your Android app is the stronger one.
- Your team **knows Kotlin**, which most Android developers do.
- You might want **shared UI** later. Compose Multiplatform gives you that option, screen by screen.
- You want a **mature ecosystem.** JetBrains reports the number of top apps using KMP has roughly doubled in a year, and there are thousands of multiplatform libraries.

KMP has its own rough edges on the iOS side. Calling Kotlin from Swift still goes through an Objective-C layer by default, and the newer **Swift export** is still early. Tools like SKIE help a lot in the meantime.

## What I'd share, either way

Whichever language you choose, the best things to share are the same:

- **Data models** and validation rules
- **Networking** and API clients
- **Business logic:** pricing, scoring, syncing and offline rules
- **Local storage** and caching

And the things I'd usually keep native:

- **UI and navigation**, unless you're happy with Compose Multiplatform's look on iOS
- **Platform features** like notifications, widgets and background work
- **Anything that should feel exactly like the platform**

In প্রশ্নব্যাংক, the shared Kotlin core holds the questions, search, exam timing and progress. The Android app uses Jetpack Compose, and the iPhone app uses SwiftUI. Each one feels native, and I write the hard logic once.

## My take

For most teams starting today, **Kotlin Multiplatform is still the safer default.** It's more mature, it has more libraries, and it gives you the option of shared UI.

But the Swift SDK for Android is genuinely good news. It gives iOS-first teams a path to Android that doesn't mean rewriting everything in a new language. Over the next year, I expect both tools to get much better, and that competition is great for all of us.

The real lesson is the same either way: **share the logic, keep the experience native.**