How We Reduced iOS App Launch Time by 60%

Source: Dev.to

Introduction

App launch time is your first impression. If your app takes more than 2–3 seconds to open, users notice; at 5 seconds they leave. We faced this on a production iOS app where cold launch time hovered around 4.8–5.2 seconds on mid‑range devices. After a focused optimization sprint we reduced launch time by ≈ 60 % (down to ~2 seconds).

Step 1 — Measure Before You Optimize

Never guess—measure. We used:

• Xcode Instruments → Time Profiler
• App Launch Metric (Xcode Organizer)
• DYLD_PRINT_STATISTICS
• Custom logging for application(_:didFinishLaunchingWithOptions:)

Baseline Numbers

Insight – Most of the time was spent before the first frame rendered, meaning startup work was blocking the main thread.

Step 2 — Find What Blocks the Main Thread

Problems we discovered:

• Heavy dependency injection at launch
• Database migration during startup
• Synchronous network calls
• Large storyboard initialization
• Too many dynamic frameworks

All happening before the first screen.

Optimizations That Gave Us 60 % Improvement

1. Defer Non‑Critical Work (Biggest Win)

Before

func application(_ application: UIApplication,
                 didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    setupAnalytics()
    migrateDatabase()
    preloadImages()
    fetchRemoteConfig()
    return true
}

After

DispatchQueue.global(qos: .background).async {
    self.setupAnalytics()
    self.migrateDatabase()
    self.preloadImages()
    self.fetchRemoteConfig()
}

// Or, even later:
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
    // non‑critical work
}

Result – Saved ≈ 1.8 seconds immediately.

2. Lazy Load Dependencies

Before

let networkManager = NetworkManager()
let cacheManager   = CacheManager()
let analytics      = Analytics()

After

lazy var networkManager = NetworkManager()

Result – Saved ≈ 400 ms (cost only incurred when the feature is used).

3. Reduce Storyboard Complexity

Initial storyboard contained 20+ view controllers, heavy Auto Layout, custom fonts, and embedded navigation.

Fixes

• Split the storyboard into smaller pieces.
• Use a lightweight launch screen.
• Move heavy views to programmatic UI.

Result – Saved ≈ 300–500 ms.

4. Optimize Dynamic Frameworks

Each dynamic framework adds launch overhead (dyld linking, symbol resolution). We had 18 frameworks.

Actions

• Merged small frameworks.
• Converted some to static libraries.
• Removed unused pods.

Result – Saved ≈ 700 ms.

5. Move Database Migration Off Startup

We were migrating SQLite on every launch.

Fix

• Run migration only if the schema version changed.
• Perform migration after the first screen appears, on a background queue.

Result – Saved ≈ 600 ms.

6. Image & Asset Optimization

Problems

• Large PNGs and unnecessary @3x assets.
• Images preloaded on launch.

Fixes

• Convert assets to WebP/HEIF.
• Load images on demand.
• Remove preloading.

Result – Saved ≈ 200–300 ms.

Final Metrics

Total improvement: ≈ 60 % faster launch.

Key Lessons Learned

Do

• Defer everything non‑critical.
• Lazy‑load dependencies.
• Measure with Instruments.
• Minimize dynamic frameworks.
• Keep the launch screen lightweight.

Don’t

• Call APIs on startup.
• Migrate the database on the main thread.
• Eagerly initialize all services.
• Load heavy storyboards.
• Block the main thread.

Quick Startup Optimization Checklist

• Use a lightweight launch screen.
• Lazy‑load services.
• Remove unnecessary frameworks.
• Defer analytics initialization.
• Perform DB work in the background.
• Avoid heavy DI containers at launch.
• Profile regularly with Instruments.

Final Thoughts

Launch time directly impacts:

• Retention
• Ratings
• Perceived quality
• Conversions

Users judge your app in seconds—literally. Treat startup performance as a feature, not an afterthought. By smartly deferring work, lazy‑loading, and removing bloat, we achieved a 60 % improvement without changing core functionality.