A phone that used to feel instant and now lags on everything is almost always down to one of a handful of causes: nearly full storage, an ageing battery that can no longer supply full power, too many apps running in the background, or a genuine hardware fault. The fix is different for each, and running the wrong one wastes time without solving anything. Here is how to work out which one you have and fix it.
Quick answer: why phones slow down
- Storage nearly full? This is the single most common cause. Free up space and performance usually recovers immediately.
- Battery old or health below 80 percent? Your phone may be deliberately throttling performance to avoid random shutdowns.
- Just updated the software? Slowdowns for a day or two after a major update are normal while the system reindexes.
- Phone is several years old and slow everywhere, even after a factory reset? That is usually a hardware limitation rather than something fixable with software.
- Slow only in specific apps? That points to the app itself, or your Wi-Fi and mobile data, rather than the phone.
Slow internet vs a genuinely slow phone
Before assuming your phone itself is the problem, rule out your connection. A weak Wi-Fi signal or poor mobile data coverage can make browsing, streaming and app loading feel exactly like a slow phone, even when the device itself is running perfectly. This is one of the most common causes of a phone that only feels slow in certain apps or locations.
- iPhone: go to Settings, then Wi-Fi, and confirm you are connected to the right network with a strong signal. If problems persist, go to Settings, then General, then Transfer or Reset iPhone, then Reset, then Reset Network Settings. This clears saved Wi-Fi passwords and network configurations, so you will need to reconnect afterwards.
- Android: go to Settings, then Network and Internet, then Wi-Fi, and check the connected network. Tap the network name, select Forget, then reconnect with the password to refresh the connection.
- If neither fixes it, try loading a website or app over mobile data instead of Wi-Fi, or vice versa, to work out whether the fault is your home network, your mobile signal, or the phone itself.
If everything is fast on a strong connection but slow the moment you switch networks, the issue is your internet rather than your phone, and no repair will fix it.
Software fixes to try first
- Restart your phone. This clears background processes and memory leaks that build up over days of use and is genuinely the fastest fix available.
- Check your storage. On iPhone go to Settings, then General, then iPhone Storage. On Android go to Settings, then Storage. Once a phone passes around 90 percent full, the operating system struggles to manage temporary files and everything slows down.
- Update your software. Manufacturers regularly release performance and battery fixes, and running an old, unsupported version can make normal tasks feel sluggish.
- Close and offload unused apps. Apps left open in the background continue to use memory and battery. On iPhone, offloading unused apps in Settings removes the app but keeps its data.
- Clear app caches and browser data. Social media apps and browsers in particular can build up several gigabytes of cached data that quietly slows the whole phone down.
- Remove live wallpapers and heavy widgets. These run constantly in the background and cost more performance and battery than they are usually worth.
- Turn off location services for apps that do not need them. Constant GPS tracking in the background is one of the heavier drains on both processing power and battery, particularly for apps you rarely open.
- Make restarting a weekly habit rather than a last resort. A phone left running for weeks at a time accumulates far more background clutter than one restarted regularly, and the difference in day-to-day speed is noticeable.
Storage almost full: the most common cause
Modern phones use spare storage space as working memory for everyday tasks like switching between apps, loading photos and running the camera. When storage gets close to full, the phone has nowhere left to work and everything from opening apps to typing a message starts to lag. The biggest space users are almost always large videos, duplicate photos synced from messaging apps, and cached data from apps you barely use. Deleting a handful of long videos or clearing WhatsApp’s media cache often fixes a slow phone in minutes, with no repair needed at all.
Malware and junk apps
On Android, apps installed from outside the Play Store, or Play Store apps that ask for far more permissions than they need, can run constantly in the background, drain the processor, and generate network traffic you never asked for. This shows up as a phone that is slow everywhere, gets warm even when idle, and burns through battery faster than it used to.
- Go to Settings, then Apps, and sort by battery or data usage to spot anything unfamiliar or using far more than it should.
- Uninstall anything you do not recognise or no longer use, particularly apps installed outside the Play Store.
- Run a scan with a reputable security app if you suspect something more serious, especially after clicking a link in a text or downloading an app from outside the official store.
iPhones are far less susceptible to this particular cause thanks to Apple’s app sandboxing and App Store review process, though the same principle of removing unused or suspicious apps still applies if you have installed anything through a third-party profile or configuration.
Hardware causes: when it is not software
If you have freed up storage, restarted, and updated the software and the phone is still slow everywhere, the cause is more likely to be hardware.
An ageing or degraded battery. As a battery wears down, it becomes less able to deliver quick bursts of power. Both iPhone and Android manufacturers build in performance throttling that automatically slows the processor down to prevent the phone randomly switching off when the battery cannot keep up. This is one of the most common causes of a phone that used to feel fast suddenly feeling sluggish, and it is also one of the easiest to fix.
Failing memory (RAM). RAM is your phone’s short-term working memory, used every time you switch between apps or the camera loads quickly. It is not something that wears out the way a battery does, but on a phone that has suffered drop or water damage, a loose or failing memory chip can cause exactly the same symptoms as general slowness, along with random app crashes or restarts. Unlike a laptop, phone memory is soldered directly to the logic board and cannot be swapped out, so a genuine RAM fault points to a board-level diagnostic rather than a part you could replace yourself.
A failing charging port or intermittent charge. A phone that is not charging reliably overnight can wake up on low battery and immediately throttle itself for the rest of the day, which feels identical to a general slowdown even though the real fault is the charging port or cable.
Past water or liquid exposure. Even a phone that survived a splash and kept working can develop light corrosion on internal connections over the following weeks, causing components to intermittently underperform. If your phone has been wet at any point and started slowing down since, this is worth ruling out. See our water damaged phone guide or book a water damage repair.
iPhone specific causes of slowdown
Check your battery health under Settings, then Battery, then Battery Health and Charging. Apple flags anything below 80 percent as significantly degraded, and this is usually accompanied by a note about peak performance capability if throttling is active. Also check that Low Power Mode is not stuck on, since it deliberately reduces background activity and visual effects to save battery. If your iPhone is still slow with a healthy battery and normal storage, our iPhone repairs team can run a full diagnostic.
Android specific causes of slowdown
Android slowdowns often come from manufacturer software layers such as Samsung’s One UI or pre-installed apps you never use running in the background. Go into Settings, then Apps, and check which apps are using the most battery and data in the background, then disable or uninstall anything you do not need. Fragmented storage on older Android phones can also contribute, particularly on devices with 32GB or 64GB of storage that are now running several years of accumulated app updates. Significant Locations and background location history, found under Settings, then Privacy, can also be worth checking on both platforms, since apps with constant location access in the background are a common hidden drain that rarely gets noticed until battery and speed both suffer.
When it is time to repair, and when it is time to replace
A battery or charging port repair on a phone that is a couple of years old is almost always worth doing, and usually solves a slowdown completely. On a phone that is five years old or more, running an operating system version close to the end of its support life, it is worth weighing up the cost of a repair against a newer, faster device. If a repair is not the right call, iExpert Market offers reliable refurbished phones at a fraction of the cost of buying new.
A simple order to troubleshoot in
With this many possible causes, it helps to work through them in the order they are most likely to actually be the problem, rather than trying everything at once.
- Restart the phone. Takes 30 seconds and fixes more than people expect.
- Check storage and free up space if it is above roughly 90 percent full.
- Confirm it is not just your Wi-Fi or mobile signal by testing on both.
- Update the operating system if you are behind on updates.
- Check battery health and consider a replacement if it has dropped significantly.
- Review background apps and permissions, and remove anything unfamiliar.
- If it is still slow everywhere with none of the above explaining it, book a diagnostic to check for a charging, RAM or logic board fault.
Frequently asked questions
Does closing background apps actually make a phone faster?
Rarely, and sometimes it makes things slower, since reopening a closed app from scratch uses more resources than resuming it from the background. Restarting the phone entirely is far more effective than manually closing every app.
Will a factory reset speed my phone up?
Often, yes, if the slowdown is caused by years of accumulated apps, cached data and background processes. It will not help if the real cause is an ageing battery or a hardware fault, so back up your data first and try the simpler fixes above before resetting.
Why does my phone slow down right after a software update?
This is usually temporary. Updates reindex Spotlight or Google search data, rebuild caches and reinstall background services, which can make the phone feel sluggish for a day or two before settling back to normal.
Does battery health really affect how fast a phone feels?
Yes. Both iOS and Android intentionally reduce processor speed on phones with a badly worn battery to prevent unexpected shutdowns, which can make a phone feel noticeably slower even though the processor itself has not changed.
Is it worth repairing an old, slow phone?
Usually, if the fix is a battery or charging port. It is worth thinking twice on very old devices that are no longer receiving software updates, where a refurbished replacement may serve you better long term.
Does Apple deliberately slow down old iPhones?
Not deliberately to force upgrades, despite the “Batterygate” controversy in 2017 when Apple admitted to throttling performance on iPhones with degraded batteries. The company’s explanation, which it still maintains, is that this was a software protection to prevent phones with worn batteries from randomly shutting off under heavy load, not a scheme to push people toward new devices. Apple now shows battery health and any active performance throttling directly in Settings, so you can check and address it yourself with a battery replacement rather than a new phone.
Still slow after trying everything?
If you have freed up storage, restarted, updated your software and your phone is still noticeably slower than it used to be, book a diagnostic and we will tell you honestly whether a battery, charging port or another repair will fix it, or whether your money is better spent elsewhere.
You might also find our guide on why is my phone not charging useful, or get in touch on our contact us page for advice on your specific model.
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