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Mobile Development · head to head

Firebase vs Kotlin Multiplatform

Firebase logo

Firebase

Mobile Development

Google's platform for building web and mobile applications with cloud backend

From
Free
Rated
-
Full reviewWebsite
Kotlin Multiplatform logo

Kotlin Multiplatform

Mobile Development

JetBrains-funded technology for sharing Kotlin business logic across iOS, Android, web, desktop and server

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Firebase spark plan limited to 1 GiB storage, 50,000 daily reads, 20,000 daily writes; Kotlin Multiplatform it shares logic, not UI, by default, so a team expecting a Flutter-style single UI codebase has to also adopt Compose Multiplatform, which is newer and less proven on iOS than on Android.
  • They diverge on capability: Firebase covers Real-time Database, Kotlin Multiplatform covers Shared Kotlin logic.
  • Prices and features above were last checked on 1 September 2026.

Where they differ

Only the attributes on which Firebase and Kotlin Multiplatform actually diverge.

Attributes where Firebase and Kotlin Multiplatform differ
AttributeFirebaseKotlin Multiplatform
Pricing modelfreemiumOpen source, no licence fee
PlatformsiOS, Android, Web, Flutter, C++, UnityiOS, Android, Windows, macOS, Linux, Web
Founded1998Unknown

Identical on both: starting price (Free), free tier (Yes), user rating (Not yet rated), category (Mobile Development).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Firebase

  • Real-time Database
  • REST API
  • Authentication
  • Google Cloud
  • Cloud functions
  • Cloud Storage
  • Web support
  • Mobile support

Only in Kotlin Multiplatform

  • Shared Kotlin logic
  • Native UI retained
  • Compose Multiplatform (optional)
  • IDE tooling
  • Gradle-based builds
  • Incremental adoption

What people use each for

The jobs each tool is most often brought in to do.

Firebase

  • Mobile app backend developmentnot Kotlin Multiplatform
  • Real-time data synchronisationnot Kotlin Multiplatform
  • Web application backendnot Kotlin Multiplatform
  • Cross-platform app developmentnot Kotlin Multiplatform

Kotlin Multiplatform

  • A company with existing separate native iOS and Android codebases wanting to stop duplicating business logic and networking codenot Firebase
  • A team that wants shared logic but is not willing to compromise on fully native UI per platformnot Firebase
  • An organisation already using Kotlin on the backend that wants to reuse the same models and validation on mobile clientsnot Firebase
  • A team evaluating Compose Multiplatform for UI sharing but wanting the option to fall back to native UI per screennot Firebase

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Firebase

  • Spark plan limited to 1 GiB storage, 50,000 daily reads, 20,000 daily writes
  • Spark plan restricts to 100 concurrent database connections
  • Spark plan limits Firebase Studio to 3 workspaces maximum
  • Document size capped at 1 MiB per document
  • Transaction time limited to 270 seconds with 60-second idle expiration
  • Maximum 100 databases per project (increase requires support request)

Kotlin Multiplatform

  • It shares logic, not UI, by default, so a team expecting a Flutter-style single UI codebase has to also adopt Compose Multiplatform, which is newer and less proven on iOS than on Android.
  • iOS interop relies on Kotlin/Native compiling to a framework consumed from Swift, and debugging across that boundary is more friction than debugging pure Swift or pure Kotlin.
  • Because logic-sharing is the whole premise, teams still need genuine iOS and Android UI expertise on staff; it does not reduce the native skills bar the way a full cross-platform UI framework aims to.
  • Build times and tooling maturity for multiplatform Gradle projects lag behind single-platform Kotlin or Swift projects, and multiplatform-specific build errors are less well documented.
  • JetBrains funds it as part of the broader Kotlin investment, so its roadmap priority competes internally with IntelliJ, Android Studio and other JetBrains commitments rather than having dedicated headcount the way Flutter has at Google.

Pricing, plan by plan

Firebase

Free
  • SparkFree
    • No-cost usage with daily-refreshing quotas
    • Cloud Firestore: up to 1 GB storage, 20K writes/day, 50K reads/day
    • Cloud Functions: up to 2M invocations/month, 400K GB-seconds/month
  • Blaze$null/variable
    • Pay-as-you-go usage beyond free tier
    • Cloud Firestore: $5/GB after 1 GB, writes beyond 20K/day at overage rates
    • Cloud Functions: $0.40 per million invocations beyond 2M/month, $0.12/GB for outbound networking beyond 5 GB/month

Kotlin Multiplatform

Free
  • Kotlin MultiplatformFree
    • Apache 2.0 licensed, unlimited apps
    • IDE tooling in the free Android Studio and free-tier IntelliJ IDEA Community
    • No paid Kotlin Multiplatform edition exists

Which should you pick?

Choose Firebase if

  • You need real-time database.
  • You want to start without paying.
  • You work on iOS, Android, Web, Flutter, C++, Unity.
  • You also want rest api.
Firebase review

Choose Kotlin Multiplatform if

  • You need shared kotlin logic.
  • You want to start without paying.
  • You work on iOS, Android, Windows, macOS, Linux, Web.
  • You also want native ui retained.
Kotlin Multiplatform review

Questions people ask

Is Firebase or Kotlin Multiplatform better?
Neither clearly leads. Firebase starts at Free and Kotlin Multiplatform at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Firebase or Kotlin Multiplatform?
Firebase starts at Free and Kotlin Multiplatform at Free.
Does Firebase or Kotlin Multiplatform run on more platforms?
Firebase runs on iOS, Android, Web, Flutter, C++, Unity. Kotlin Multiplatform runs on iOS, Android, Windows, macOS, Linux, Web.
Can I use Firebase for free?
Both have a free tier, so you can try either at no cost before committing.
What is Firebase best used for?
Firebase is most often used for mobile app backend development, real-time data synchronisation, web application backend, cross-platform app development. Of those, mobile app backend development and real-time data synchronisation are not what Kotlin Multiplatform is typically brought in for.
What can Firebase do that Kotlin Multiplatform cannot?
Firebase covers Real-time Database, REST API, Authentication, Google Cloud. Kotlin Multiplatform covers Shared Kotlin logic, Native UI retained, Compose Multiplatform (optional), IDE tooling.

Answered from the vendors’ own pages

Firebase: What are Firebase's free tier limits?

Firebase Spark plan includes no-cost daily-refreshing quotas: Cloud Firestore up to 1 GB storage with 20K writes and 50K reads per day; Cloud Functions up to 2M invocations monthly; Cloud Storage 5 GB-months with 100 GB downloads monthly; Hosting 10 GB storage and 360 MB daily data transfer; Realtime Database up to 1 GB storage. No payment method required.

Source
Kotlin Multiplatform: Does Kotlin Multiplatform replace my native UI code?

Not by default. It shares business logic and data layers; UI stays native per platform unless you separately adopt Compose Multiplatform.

Firebase: How much does Firebase Blaze plan cost?

Firebase Blaze is pay-as-you-go beyond free tier limits. Pricing includes Cloud Firestore storage at $5/GB after 1 GB; Cloud Functions $0.40 per million invocations beyond 2M monthly; Cloud Storage $0.026/GB beyond 5 GB; Hosting $0.15/GB beyond 360 MB daily. New eligible customers receive $300 free credit.

Source
Kotlin Multiplatform: Is there a paid version?

No. It is Apache 2.0 licensed and free, funded by JetBrains as part of the Kotlin project.

Firebase: Which Firebase services are always free regardless of tier?

A/B Testing, Analytics, App Check, Cloud Messaging, and Crashlytics are offered at no cost on both Spark and Blaze plans, with no usage limits stated.

Source
Kotlin Multiplatform: Do I need Compose Multiplatform to use it?

No, they are separate. You can share only logic and keep fully native UI on each platform indefinitely.

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