First, wait 24 to 48 hours
This is the single most important piece of advice, and the one almost nobody follows. An update does not finish when the progress bar does. Afterwards, your phone quietly does a large amount of housekeeping:
- Reindexing files so search and photos can find everything again
- Rebuilding caches that apps rely on for speed
- Re-optimising apps for the new system version
- Re-learning your usage patterns for battery and performance management All of that competes for the processor and storage while you are trying to use the phone, so everything feels slower and the battery drains faster. On most phones this settles within a day or two. Judging an update in its first hours is like judging a house move while the boxes are still everywhere.
The apps have not caught up yet
Your operating system updates on one day. Your apps update on their own schedules. In the gap, some apps run on code written for the old system, which can mean crashes, freezes, or an app that keeps the processor awake in the background, draining battery and slowing everything else. This is the most common cause of a slowdown that lasts beyond the first two days. The fix is unglamorous: update all your apps, and if one app in particular misbehaves, delete and reinstall it so it gets a clean start on the new system.
New software is heavier than old software
Every major update adds features: new animations, new always-on services, stronger security checks, more background intelligence. Those features are designed and tested mainly on the newest phones, with faster processors and more memory. Your two- or three-year-old phone gets the same features but not the same headroom. That is not sabotage; it is the ordinary cost of progress. A phone that shipped with 4GB of RAM running software designed for 8GB or 12GB devices will feel the squeeze, especially when several apps are open at once.
Full storage makes everything worse
When your storage is nearly full — roughly above 85 to 90 percent — your phone struggles to write temporary files, manage caches, and shuffle data around. Flash storage also slows down when its controller has few empty blocks to write to. An update itself eats gigabytes, which can push a nearly-full phone over the edge. The rule of thumb: keep at least 10 to 15 percent of your storage free. If you are above 90 percent full, freeing space is often the single biggest speed fix available, update or not.
The battery angle
Batteries age. After a couple of years, a lithium-ion battery holds less charge, and phones may quietly limit peak processor speed to prevent unexpected shutdowns when an aged battery cannot deliver a sudden burst of power. An update can make this visible. If your phone is several years old, feels slow, and dies quickly, a battery replacement can genuinely make it feel new again. Our guide to how lithium-ion batteries work explains why batteries fade and what "battery health" percentage really means.
What about planned obsolescence?
In 2017, Apple admitted it was slowing some older iPhones with worn batteries to prevent shutdowns, without clearly telling users at first. It apologised, paid settlements, and added battery-health transparency. That episode earned the industry lasting distrust. But there is a difference between "software gets heavier and old hardware struggles" and "manufacturers deliberately brick old phones." What looks like sabotage is usually the combination above: settling-in work, lagging apps, fuller storage, and heavier software on ageing hardware.
What to do, in order
- Wait 48 hours with the phone charged and ideally idle overnight, so background optimisation finishes.
- Update all apps, then reinstall any single app that still misbehaves.
- Free storage to at least 10–15 percent free — photos, videos and unused apps first.
- Restart once after the settling period, not repeatedly during it.
- Check battery health (Settings → Battery on both iPhone and Android); below 80 percent, consider a replacement.
- Reduce motion and background refresh for heavy apps if your phone is older. If none of that helps after a week, the update may have a genuine bug. Check whether others with your exact model report the same problem; manufacturers usually ship a fix within weeks for widespread issues. And if you want to understand the processor side of the story, our explainer on how CPUs actually work covers why clock speed, cores and memory decide how fast a phone can feel.
Takeaway checklist
- Wait 24–48 hours first — reindexing and cache rebuilding cause most early slowness.
- Update your apps — unoptimised apps are the top cause of lasting post-update lag.
- Keep 10–15% storage free — a nearly full phone slows down everything.
- Check battery health — an aged battery can trigger quiet performance limits.
- Heavier software on older hardware is normal — it is progress, not sabotage.
- Still slow after a week? Look for a model-wide bug report and wait for the fix — or consider a battery replacement before a new phone.
