Kotlin Multiplatform Explained: A New Way to Share Code Across iOS and Android

Key Takeaways

• Kotlin Multiplatform (KMP) lets you write code once. Use it on iOS and Android.
• It shares the logic, like data and rules. The screens can stay fully native.
• The biggest win is speed. One team builds core features once.
• The biggest catch is setup. iOS teams must learn a little Kotlin.
• KMP suits teams that want native feel without building everything twice.

Kotlin Multiplatform use jumped from 7% to 18% in one year. That is more than double. The data comes from the 2024 and 2025 JetBrains surveys. Teams are clearly paying attention.

Building for two platforms hurts. You write the same login flow twice. You fix the same bug twice. You explain the same rule to two teams. It eats time and money. Worse, the two apps slowly drift apart. Kotlin Multiplatform development takes a different path.

You will learn how it works. You will see what it shares and where it falls short. We also look at big apps that use it. Let’s start with the basics.

What Is Kotlin Multiplatform?

Kotlin Multiplatform, or KMP, lets you write code once. You then run it on Android, iOS, desktop, web, and servers. Think of it as a shared toolbox. Both apps reach into the same box.

You keep what should feel native. Screens can stay in Swift and Kotlin. Only the shared logic moves into one place.

JetBrains first introduced the idea in 2017 with Kotlin 1.2. It reached stable status in November 2023. That is a clear sign of maturity.

Kotlin Multiplatform Mobile vs KMP

You may see the name Kotlin Multiplatform Mobile, or KMM. That was the older label for mobile use. Today JetBrains uses one name, KMP. It covers mobile, desktop, web, and backend.

Older posts about KMM still apply.

Who Built It and Why

JetBrains built KMP. They also make Kotlin and IntelliJ IDEA. Their goal was simple. Stop teams from writing the same logic twice.

Google joined in too. At Google I/O 2024, Google announced official support. It covers sharing business logic between Android and iOS.

KMP sits in a busy space. Many teams weigh cross-platform development against fully native builds. KMP tries to give you both. See where it fits among other mobile app development technologies and tools.

How Does Kotlin Multiplatform Work?

KMP splits your project into parts. Some parts are shared. Others belong to one platform. Here is the simple version.

Common Code

Common code is the shared part. You write it once in Kotlin. It holds the rules of your app.

Good examples include:

• Data models
• Network calls
• Validation rules
• Caching logic

Kotlin then compiles this code for each platform. Android gets normal Kotlin output. iOS gets a native framework.

Platform-Specific Code

Some things differ by device. Cameras, push alerts, and biometrics are good examples. You write these parts natively.

The Android side uses Kotlin. The iOS side uses Swift. Each side stays clean and familiar.

The Expect and Actual Setup

This is the glue. In shared code, you say what you need. You use the word expect. Each platform then supplies the real answer with actual.

• Shared code
  expect fun deviceName(): String
• Android
  actual fun deviceName(): String = “Android”
• iOS
  actual fun deviceName(): String = “iPhone”

The shared code does not care how it works. It just asks. Each platform replies.

Shared code vs native code

Kotlin is only one choice. Compare it with other programming languages for mobile app development.

How Much Code Can You Share?

Less than you might hope, or more. It depends on your app. Most teams start small and grow.

Business Logic

This is the sweet spot. Reports say 80% to 90% of business logic is often shared. That covers networking, data models, caching, and rules.

Forbes is a good example. Its Kotlin case study reports over 80% shared. That covers iOS and Android.

Networking and Data

Networking is a natural fit. Both apps call the same servers. Both parse the same data. Why write it twice?

Shared data code also means fewer surprises. A bug fix lands on both apps at once.

UI with Compose Multiplatform

You can also share screens. Compose Multiplatform makes that possible. It is stable for iOS, Android, and desktop. Web support is in Beta.

Compose Multiplatform for iOS went stable in May 2025. That was version 1.8.0. Many teams still share logic first. They add shared screens later.

Sharing more code changes your plan. See where shared modules fit in the mobile app development process.

What teams usually share first

Benefits of Kotlin Multiplatform

KMP helps in a few clear ways. Here is the short list.

• Faster releases. One feature is built once, then shipped twice.
• Fewer bugs. One set of rules means fewer mismatches.
• One logic source. Both apps behave the same way.
• Native performance. Your screens stay native, so apps feel right.
• Lower cost. Less duplicate work means a smaller bill.

Speed matters most. One industry estimate says cross-platform builds launch 40% to 60% faster. That compares to two native apps. Treat it as a rough guide. Your results will vary.

Two native apps vs a KMP build

Budget is often the deciding factor. See what drives mobile app development cost. A good partner plans shared modules early. A Cubix team does exactly that. We map which parts to share. The rest stays native. You spend less without losing quality.

Limitations of Kotlin Multiplatform

KMP is not perfect. Know the trade-offs before you commit.

Learning Curve for iOS Teams

iOS developers know Swift. Kotlin feels new. Xcode and Android Studio also work differently. That takes time to learn.

Smaller Library Pool

The KMP ecosystem is young. In the 2024 KMP survey, 23.8% of respondents had used it under six months. The community is still growing. Some libraries are missing. You may write a few tools yourself.

Build and Tooling Issues

Builds can feel slow. Debugging across Kotlin and Swift takes practice. IDE support keeps improving. IntelliJ IDEA and Android Studio now offer a KMP plugin. Still, expect a few bumps early on.

When KMP Is Not the Right Pick

KMP may not fit every project. Skip it if:

• Your app is tiny and simple.
• Your team has no Kotlin skills and no time to learn.
• You want a fully shared UI on day one, with zero native code.

Teams with strong Android skills gain the most. Compare the two languages in our post on Kotlin vs Swift.

None of these gaps are dealbreakers. At Cubix, we plan for each one before coding starts. We pick proven libraries. We set up clean builds. We train the team where needed.

Kotlin Multiplatform vs Flutter

Both tools save effort. They just do it differently.

Language and Setup

KMP uses Kotlin. Flutter uses Dart. Android teams already know Kotlin. Dart is new to most developers.

KMP also drops into an existing app. You can share one module at a time. Flutter usually needs a fuller commitment.

UI Approach

Flutter draws its own screens. Every pixel comes from Flutter. That gives you a matching look on both platforms.

KMP keeps native screens by default. Your iOS app looks like iOS. Your Android app looks like Android. You can share UI with Compose Multiplatform if you want.

Performance

Both perform well for most apps. KMP compiles to native code. Flutter compiles to native code as well. Differences show up in heavy or unusual cases.

KMP vs Flutter vs React Native

Now the numbers. In the 2024 Stack Overflow survey, 9.4% of developers used Flutter. React Native came in at 8.4%. The gap is small.

KMP is tracked differently, so it is not in that chart. Building Android first? Read our Android app development guide.

Is Kotlin Multiplatform Production Ready?

Yes. That answer has changed fast. Not long ago, teams worried it was too new. Now big brands ship it every day.

Stability and Google Support

KMP core went stable in November 2023. Google announced official support in 2024. Compose Multiplatform for iOS went stable in May 2025.

Adoption tells the same story. Remember the jump from 7% to 18%?

Companies Using KMP

Many well-known teams use it. Some share a little. Some share nearly everything.

Real companies using KMP

The scale is real. Reports say McDonald’s app handles 6.5 million purchases each month. A Kotlin case study cites over 30 million monthly Cash App users.

Cubix builds KMP apps with production in mind. We start with a solid shared core. We test it on both platforms. Then we scale it safely.

How Long Does It Take to Learn?

It depends on where you start. Android developers move fastest.

For Android Developers

You already know Kotlin. That is most of the work. Expect a few weeks to learn the setup. The expect and actual pattern comes fast.

Kotlin is well loved. In the 2024 JetBrains survey, 75% of Kotlin users were satisfied. That helps teams stay motivated. Weighing Kotlin against Java? Read Kotlin vs Java.

For iOS Developers

Swift developers face a bigger jump. Kotlin syntax looks familiar, but the tools are new. Plan for a slower start. Pairing with an Android teammate speeds things up.

Most new adopters are existing Android teams. They stretch their Kotlin skills into iOS.

A Simple Learning Path

1. Learn Kotlin basics.
2. Build a small shared module.
3. Connect it to a simple Android app.
4. Connect the same module to an iOS app.
5. Add networking and data storage.
6. Try Compose Multiplatform for shared screens.

You can skip much of this curve with the right partner. Cubix uses mixed teams. Our Android and iOS developers work side by side. Your project never waits on training.

The Future of Kotlin Multiplatform

The direction is clear. KMP is growing, and the tools are getting better.

Compose Multiplatform for web is still in Beta. In the 2024 KMP survey, 46.7% had considered KMP and planned to explore it. That points to more growth.

Here are the trends to watch:

• More shared UI. Compose Multiplatform keeps maturing.
• Web support. Beta today, stable later.
• Better tools. The IDE plugin keeps improving.
• More libraries. The ecosystem grows every month.
• Gradual adoption. Teams add KMP one module at a time.

Why Choose Cubix for Kotlin Multiplatform?

Picking a partner matters as much as picking a tool. Cubix builds mobile apps that ship on time and scale well. We use KMP where it makes sense.

Here is what you get with Cubix:

• Experienced mixed teams. Android and iOS developers work together.
• Smart planning. We decide what to share and what to keep native.
• A clear process. You see progress at every stage.
• Quality checks. We test shared code on both platforms.
• Honest advice. If KMP is not right, we will tell you.

We also offer full android app development services for dedicated support.

Build Your App With Cubix

Kotlin Multiplatform gives you a smarter way to build. You share the logic. You keep the native feel. You save time and money.

When you work with Cubix, you get:

• A free review of your app idea
• A clear plan for what to share
• A realistic timeline and budget
• A team that builds for both platforms

Ready to start? Book a free consultation with Cubix today. Tell us your idea. We will show you the best way to build it.

FAQs

1. What is Kotlin Multiplatform and how does it work?

It is a JetBrains tool for sharing code. You write shared logic in Kotlin. Each platform then uses that code.

2. Can you really share code between iOS and Android with Kotlin?

Yes. Kotlin compiles to a native iOS framework. Your Swift app can call it directly.

3. How much code can you actually share with KMP?

Teams often share 80% to 90% of business logic. Sharing screens is optional. The amount depends on your app.

4. How does Kotlin Multiplatform compare to Flutter?

KMP shares logic and keeps native screens. Flutter draws its own screens. KMP suits Android-heavy teams. Flutter suits teams wanting one look everywhere.

5. What are the benefits of using Kotlin Multiplatform?

You ship faster and write less duplicate code. Bugs drop. Apps keep a native feel.

6. What are the limitations of Kotlin Multiplatform?

iOS teams must learn Kotlin. The library pool is smaller. Tooling can feel rough at times.

7. How long does it take to learn Kotlin Multiplatform?

Android developers need a few weeks. iOS developers may need longer. Practice on a small shared module first.

8. What companies are using Kotlin Multiplatform?

Netflix, McDonald’s, Cash App, and Forbes use it. Philips, VMware, and Google Docs appear in Kotlin case studies too.

9. What’s the future of Kotlin Multiplatform development?

It looks bright. Adoption is rising, and Compose Multiplatform keeps growing. Web support is next.