If you’re still holding onto an iPhone 5s running iOS 9, you’ve probably been staring at that update notification for a long time — maybe years. The hesitation is understandable: old iPhones and new iOS versions have a rocky history, and nobody wants to turn a perfectly working phone into a sluggish brick. But in this specific case, the answer is clear.
Yes — you should update your iPhone 5s from iOS 9 to iOS 12. It’s the rare update that’s genuinely worth it on old hardware. But there’s one critical catch you need to understand first, so read the warning below before you tap that button.
The one catch: it’s a one-way trip
Let’s get the scary part out of the way. Updating from iOS 9 to iOS 12 is irreversible — Apple stopped signing iOS 9 long ago, so there is no way to downgrade back once you’ve updated. If something about iOS 9 is precious to you (a specific old app version, a jailbreak, the old design), it will be gone for good. Back up your iPhone to a computer or iCloud before you do anything, so your photos, messages, and data are safe no matter what.
Also worth knowing: iOS 12 is the final iOS version the iPhone 5s will ever get. There is no iOS 13 for this phone. So this isn’t the start of an endless update treadmill — it’s one jump, and then you’re done, on the best software your 5s will ever run.
Reason 1: Performance stays on par with iOS 9
This is the big surprise. iOS 12 was specifically engineered to run well on older devices — Apple made speed on aging hardware a headline feature of the release. Independent speed tests on older iPhones running iOS 12 showed apps launching faster and the system feeling more responsive than expected. On the 5s, everyday performance is roughly on par with iOS 9, not the slowdown disaster that past updates caused. You can even watch side-by-side iOS 9 vs iOS 12 speed comparisons to see it with your own eyes.
Reason 2: Years of security fixes
iOS 9 stopped receiving security updates a very long time ago. Every vulnerability discovered since then — and there have been many — remains unpatched on your phone. iOS 12 closes all of those holes. If you use your 5s for anything involving accounts, banking, email, or personal data, this alone justifies the update. Apple’s iOS 12 security and support information details what’s covered.
Reason 3: Apps actually work again
On iOS 9, you’re stuck with ancient versions of apps — if they install at all. Developers have long since dropped iOS 9 support, so you’re missing features, bug fixes, and in many cases the apps simply refuse to download. iOS 12 opens the door to far more current app versions from the App Store. If you’re running out of space juggling old apps, here’s a guide to which built-in iPhone apps you can delete to free up room.
Reason 4: Genuinely useful new features
Jumping from iOS 9 to iOS 12 skips three major versions, so the feature haul is substantial: a proper screenshot editor with markup, a smarter Siri with shortcuts, interactive notifications you can act on without opening apps, widgets on the lock screen, a redesigned Control Center, grouped notifications that stop the avalanche, and Screen Time for taming usage. Messages, Photos, Music, the App Store, and Notes all got meaningful upgrades too.
And if you ever decide updates aren’t for you in the future, you can learn how to completely block iOS updates on iPhone — though on the 5s, there are no more updates coming anyway.
If it still doesn’t work
If the update fails or the phone feels off afterward, don’t panic. First, make sure you have enough free space — iOS updates need several gigabytes to install; delete unused apps and old videos if you’re short. If the phone gets stuck during the update, connect it to a computer and restore through Finder or iTunes. And if performance disappoints after updating, try a clean restore and set up as new rather than from a backup — it often clears out years of accumulated cruft.
Frequently asked questions
Can I go back to iOS 9 if I don’t like iOS 12?
No. Apple no longer signs iOS 9, which means iTunes/Finder will refuse to install it. The update is permanent. This is why the backup-before-you-update advice matters — it’s your only safety net.
Will iOS 12 make my iPhone 5s slower than iOS 9?
In real-world use, no. iOS 12 was optimized for older devices in a way previous releases weren’t, and speed tests show the 5s holding its own against iOS 9. Individual results vary depending on battery health and storage, but a dramatic slowdown is not the expected outcome here.
The bottom line
Updating an iPhone 5s from iOS 9 to iOS 12 is one of the safest “should I update?” bets in iPhone history: comparable performance, years of security patches, working apps, and a pile of genuinely useful features — with iOS 12 as the final, stable destination for this phone. Just remember the golden rule: back up first, because there’s no going back.
