Even beautifully designed apps can feel sluggish. Animations stutter, scrolling lags, or screens take too long to load. If you’ve invested in building an app with Swift and users are complaining it feels slow or unresponsive — this article is for you.
We’ll break down the most common reasons Swift apps feel slow and what your team can do to fix them — using language that’s friendly to both product managers and technically curious founders. You don’t need to read assembly code to follow along, but we’ll also peek under the hood to give you the real reasons behind performance bottlenecks.
Recognized consistently on Clutch as a top software development company, Volpis has years of experience delivering Swift solutions to businesses across a wide range of industries. If you’re looking to hire Swift developers who know how to deliver smooth, high-performance apps, Volpis can help.
1. Inefficient UI Rendering
The user interface (UI) is everything the user sees and interacts with. In SwiftUI or UIKit, poorly structured views or deep hierarchies can cause unnecessary re-renders.
What to watch for:
- Sluggish screen transitions
- Jittery scrolling
Fixes:
- Use LazyVStack and view diffing in SwiftUI
- Optimize cell reuse in UITableView or UICollectionView
- Minimize layout recalculations by using fixed sizes or caching where possible
2. Main Thread Bottlenecks
All UI rendering in iOS happens on the main thread. If your business logic, image decoding, or network parsing happens there too — it blocks the UI.
Signs:
- The app freezes during API calls or content loading
- Buttons don’t respond instantly
Fixes:
- Offload heavy tasks to background threads using DispatchQueue or Task { }
- Leverage Swift’s async/await for cleaner asynchronous logic
- Profile with Instruments > Time Profiler to locate main-thread work
3. Retain Cycles & Memory Leaks
If memory isn’t managed well (e.g., closures strongly capturing self), the app can become sluggish over time or even crash.
Symptoms:
- Performance degrades the longer the app is open
- Repeating the same navigation flow causes slowdowns
Fixes:
- Use [weak self] in closures
- Inspect memory graphs in Xcode
- Explicitly deinit and clean up observers, delegates, and bindings
4. Inefficient Image Handling
Images are performance-heavy. If they’re uncompressed, too large, or not cached — the UI suffers.
Signs:
- Delays in image loading
- Choppy scrolling in media-heavy lists
Fixes:
- Resize images server-side or during fetch
- Use libraries like SDWebImage or Kingfisher for caching and decoding
- Use Image(uiImage:) with care in SwiftUI — prefer async image loaders
5. Scroll Performance in Long Lists
Modern UIs often involve feeds, lists, or carousels. Poorly implemented, they introduce dropped frames.
Causes:
- Overpopulated views rendered all at once
- Dynamic height calculations done synchronously
Fixes:
- SwiftUI: Use LazyVStack instead of VStack
- UIKit: Use reusable cells and estimate cell heights
- Defer non-visible content loading until scroll settles
6. Excessive Animations or Effects
Animations can enhance UX — but layering too many can overwhelm the GPU, especially on older iPhones.
Signs:
- FPS drops during transitions or navigation
- Animation stutters during scroll
Fixes:
- Minimize the number of simultaneous animations
- Avoid animating opacity, blur, or shadows unnecessarily
- Test animations on low-end devices
7. Not Leveraging Instruments & Profiling
You can’t improve what you don’t measure. Apple’s developer tools provide deep insights into where your app struggles.
Tools to try:
- Time Profiler: Pinpoints long-running functions
- Leaks & Allocations: Tracks memory usage and leak sources
- Core Animation: Measures render time and dropped frames
Pro tip:
Run profiles under realistic conditions — real device, bad network, background apps open — to catch real-world slowdowns.
8. Improve Perceived Performance with UI Feedback
Sometimes, even fast apps feel slow because the user is left staring at a blank screen.
Suggestions:
- Show ProgressView in SwiftUI or spinners in UIKit during long tasks
- Use skeleton views or shimmer placeholders while data loads
- Implement optimistic UI updates when possible (e.g., show cached data instantly)
Conclusion
Performance isn’t just about how fast your code runs — it’s about how fast your app feels. With modern tools like Swift Concurrency, profiling instruments, and efficient UI architecture, you can create apps that feel buttery smooth.
Whether you’re managing a team or building the product yourself, a mid-level understanding of performance principles will help you build better mobile experiences.
If you’re looking to build a custom app for your business, you can reach out to the Volpis team via [email protected] with any questions.
