4 Reasons Why You Might Want to Reinstall macOS

Ben Stegner Updated 02-10-2019

A longtime Windows truism proposes that you need to reinstall the operating system often for best performance. But while there are times when it’s appropriate to do so, it’s not as vital a step as some propose.


As a Mac user, you might be curious if it’s the same case for macOS. Do you need to reinstall macOS regularly, and why should you ever reinstall the OS? Let’s dig into this question and the reasons behind it.

Do You Ever Need to Reinstall macOS?

Factory Reset Mac featured

Before we get into the motives for doing so, we should be clear that yes, there are some good reasons to reinstall macOS. However, this doesn’t mean that reinstalling it regularly is necessary.

macOS is a stable operating system that takes pretty good care of itself. Most users can use the copy of macOS that came with their system for years and never experience any problems. This is especially true since Apple introduced System Integrity Protection in OS X El Capitan, which limits user access to protected system files.

When you have a problem on your Mac, reinstalling the OS should be near the bottom on your list of troubleshooting steps. Let’s look at some situations where reinstalling macOS is a good idea, plus alternative ways to deal with these problems first.


1. When Your Mac Has a Serious Problem

An angry businessman frustrated with problems on his laptop
Image Credit: IzelPhotography/Depositphotos

The main reason most people would reinstall macOS is because their system is completely messed up. Maybe error messages pop up constantly, software won’t run correctly, and other usability issues prevent you from working normally. In extreme cases, your Mac might not even boot.

While rare, this is more likely to occur with power users who regularly play with new software and make tweaks to system settings. However, it can happen to anyone.

If your Mac has a major issue like this, we recommend first trying some other troubleshooting tools. Have a look at our list of the best free tools to fix common macOS problems The 8 Best Free Mac Tools to Detect and Fix Common macOS Problems Every Mac user should keep these 8 tools around to fix any problems that may arise, like malware, hardware issues, and more. Read More for lots of help.


For example, you can use the built-in Disk Utility tool to check for errors with your storage disk. Apple also provides diagnostic tests to help you check for hardware failures. And third-party customization tools like OnyX offer easy maintenance utilities for when something goes wrong.

If these don’t fix your problem, proceeding with a macOS reinstall is a good idea.

2. When Your Mac Is Really Slow

Snail on laptop keyboard

Even if your Mac doesn’t have a critical problem, it might still run at a snail’s pace. When this happens, we first recommend reviewing common mistakes that slow your Mac down 7 Common Mistakes That Slow Your Mac Down Is your Mac running slow? By changing some of your computing habits, you could improve its performance. These 7 big mistakes can slow down your Mac. Read More . You might need to remove some startup programs, run updates on your system, or clean out your storage drive to fix this issue.


But if none of these fixes have an effect, reinstalling macOS can likely help speed up your system. This is especially the case if your Mac is approaching a decade of life. If you do have a really old system, you may need to follow our tips for making an old Mac feel like new beyond an OS reinstall.

3. When You’re Selling Your Mac

Because Macs hold their value for so long, you can often resell your machine years after you bought it and make some of the cost back. Whether you plan to sell your Mac online or just give it to a friend, you don’t want the new owner to have access to all your files.

The easiest way to wipe out your own configuration and prepare the Mac for the next person is to reinstall the OS. When you do this, you can erase your storage drive so they can’t access any of your old data.

We’ve looked at how to sell your Mac safely and for the best price How to Safely Sell Your MacBook or iMac for the Best Price Don't risk your privacy and personal data by selling your Mac without erasing it first! Read More , so take a look at that for more information.


4. When You Want to Downgrade macOS

Most of the time, upgrading to the latest version of macOS is a painless experience. Doing so grants access to new features, plus better performance a lot of the time.

But maybe you regret updating the OS on your Mac. Perhaps the latest version made a change that affects your workflow, or maybe it just doesn’t run well on your older machine. In those cases, downgrading macOS is a viable option.

Unfortunately, Apple doesn’t offer an official solution for downgrading macOS. You’ll have to follow our guide to downgrading macOS 3 Ways to Downgrade to an Older Version of macOS Want to downgrade your Mac to a previous version of macOS? Here are several ways to revert versions if you're not happy. Read More to use workaround methods for this. There’s no in-place downgrade option, making this another instance where you have to run a fresh install.

How to Reinstall macOS When Needed

Now that we’ve looked at the few cases where reinstalling macOS makes sense, how do you actually perform the reinstall process?

We’ve covered the complete process for reinstalling macOS How to Reinstall macOS for a Fast and Squeaky Clean Mac Need to restore your Mac to factory settings? Here's how to install a fresh copy of macOS and erase everything. Read More , so be sure to read that for full details. Here we offer a brief summary of the procedure.

Before You Start the Process

maOSs Time Machine Backup

First, make sure you have all your files backed up. You can do this using the built-in Time Machine or another backup solution. While you can reinstall macOS and keep your personal data, backing up is still a smart idea. You may also want to generate a list of installed apps on your Mac 4 Ways to Generate a List of Installed Apps on Your Mac Here are several ways to list every installed application on your Mac and save them to a text list for reference. Read More so you don’t forget what you had installed.

Next, you should sign out of Apple services like iCloud, iTunes, and iMessage. Some of these only let you use your account on a certain number of devices, so you don’t want a computer that’s no longer around to use a spot.

Reinstalling Through macOS Recovery

Reinstall macOS from utilities

When you’re ready to reinstall, shut down your Mac, then reboot while holding Cmd + R. After a few moments, you’ll see the macOS Utilities screen. If you simply want to reinstall macOS without losing any data (to fix issues or get a clean start), select Reinstall macOS from the list.

However, if you want to erase everything on your computer first (such as when selling your machine), you’ll need to enter Disk Utility before reinstalling. Select your disk on the left side of the utility, then use the Erase tab to wipe it clean.

Finally, you can walk through the steps in the Reinstall macOS option. After some time, the reinstall process will complete. You can quit here if you’re selling your system, or continue through the welcome steps to set up your Mac again.

When You Might Need to Replace Your Mac

It’s clear that while you don’t need to reinstall macOS regularly, it can come in handy in certain circumstances. If you fall under any of the above situations, try an OS reinstall if the other troubleshooting steps didn’t fix your problem.

Thankfully, Apple makes it easy to reinstall macOS, so the bulk of the time is just waiting for the process to complete. If reinstalling doesn’t fix your issue, it may be time to replace your Mac 6 Signs It's Time to Replace Your Mac How long do Macs last? What are the signs that let you know when to get a new Mac? Here's when you should replace your Mac. Read More .

Related topics: Computer Maintenance, Install Software, Mac Tips, Troubleshooting.

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  1. Tejan Saien
    September 26, 2019 at 2:05 am

    I have been facing battery drain issues lately and have tried reinstalling it.

  2. Micharel
    May 25, 2016 at 12:34 am

    Starting on an Apple ][e in 1983, I have been using Macs since the mac classic. As a power user, I have had to reinstall Mac OS MANY times... no matter the version. And also my girlfriends Macbook whenever she complains about its performance (~once per year). And yes I have tried ONYX and other cleaning solutions, to no avail.

    A fresh OS install does usually speed up your machine. I reinstall every time my machine starts acting laggy, or crashes. I have an SSD, so there really should not be any lag, but my Macbook's still get issues every few months... I am about to reinstall this evening since my Macbook has really been acting noticeably slow over the past few weeks.

    I also support a Mac farm at work, for developer use. The Mac's (2 servers, and 4 mini's) each need to be rebooted approximately once every month or two, as they really act weird: display errors, graphical glitch issues, and generally high latency. I reinstall each f those machines OS's approximately every 6 months, as the developers notice the difference in accessibility which compounds over time.

    • Chris
      April 25, 2017 at 8:05 pm

      Amen! Nice to see a post based in reality. I support a fleet of over 100 macs and about 50 Windows machines at a university and I regularly have to reinstall BOTH Mac OS and Windows on my fleet. Macs are great but they are not the flawless machines they are made out to be. Macs need anti-virus, Mac OS software crashes, Macs needs to have their OS reinstalled for many reasons as discussed above. The Mac universe in general would benefit so much if there was way more reality and less completely false "It just works." talk in forums and article posts such as these.

  3. isabella
    April 1, 2016 at 3:17 pm

    my mac air is only a couple months old and freezes once a day every day when using safari (not sure if this is just a co-incidence or not as i use the internet a lot), would completely restoring it help?


  4. WickedStorm
    February 16, 2016 at 2:40 pm

    Would it be good to re-install when you change your hard drive ? From HHD to SSD ?

    • Justin Pot
      February 16, 2016 at 3:08 pm

      That's going to be the simplest approach, otherwise you could try cloning your drive or restoring from Time Machine.

      • Anonymous
        February 17, 2016 at 3:14 am

        Thank you. I did swap the HHD drive for SSD a month ago. I did clone the drive before the operation. But since that swap,the macbook is lagging, getting hot and doing some funny stuff. I did reset the SMC but still it was not operating as good as before the swap. So yesterday, I did re-install the OSX. Hopefully it will solve these issues.

  5. Dianne
    January 25, 2016 at 12:29 pm

    I was having issues at machine booted immediately into SAFE mode all by itself. Diagnostics determined no errors. MAC support had me reinstall OS X, but I did not have to back up or re-install a single thing. All my programs and files remained, even my virtual drive. Literally everything that is an application or info that resides in an application remained untouched. what was affected/corrected were the "deep files". What kind of a re-install is that? (i held Command-R at startup)...I am up and running as normal, and perhaps? a tad faster?

    • Justin Pot
      January 25, 2016 at 3:24 pm

      I'm just glad that your computer is working again, that must have been a pretty weird problem.

  6. John B
    November 26, 2015 at 5:45 pm

    Really an excellent contribution, Justin. This is the kind of real-world-decision-making help I didn't find on the Apple Support site. I'm bookmarking your site and looking forward to discovering more practical utility information of this type.

    We may come to think of our Mac as "running slow"; but, maybe that is just a perception rather than a truth. Is there any software out there that can test the theory? For example, is there software that can detect when processes take too long? I recognize that "too long" can be a complex perspective; however, you get the idea.

    Appreciate Evilplankton's entry as well.

    • Justin Pot
      November 28, 2015 at 3:42 pm

      Hey John, thanks for stopping by! Really glad the article helped you.

      I can't think of any benchmarks that check whether your computer is being slowed down by software issues, it's really more of a subjective thing. It might be a good idea, though. Hmm...

  7. Anonymous
    November 11, 2015 at 1:13 am

    This weekend I backed up and wiped my hard drive.I had some games on my mac and a few passive apps (e.g. caffeine) and thousands of files, maybe 1/10 of which I used regularly. My mac pro got so buggy for some reason time machine wasn't working out (I bought a third party external hard drive 1 TB, which worked fine before) and disk cleanup was pointless. Now my mac is running faster, way less lag, and fewer error messages. 2012 Mac Pro 13"

  8. Ron
    March 30, 2015 at 6:03 pm

    I have a Mac Pro currently running Yosemite that has been upgraded _at least_ twice (from Lion to Mountain Lion then to Yosemite? I don't remember the exact path). In its current state, it frequently reaches a point where it doesn't want to boot normally. The progress bar appears to reach about 50% and then stays there indefinitely. When it does this, resetting PRAM and/or SMC doesn't help. What consistently restores the system to booting normally is booting to recovery mode and using Disk Utility to run a permissions repair on the Macintosh HD (boot) volume. After running the repair and restarting, the Mac boots normally.
    I haven't yet tried YASU or Onyx, as you suggest. Do you think it's worth trying these for a more permanent solution? Or is this to be expected with Yosemite (even for clean installs) and I should keep doing what I'm doing and wait on a patch...or try something else? The system is running well otherwise, and with all the installed applications, I dread the thought of doing a clean install, particularly if it doesn't resolve the problem.

    Thank you!

    • Justin Pot
      March 31, 2015 at 2:20 pm

      I'd give the above tools a try first, then do a reinstall if the problem persists. I'm pretty sure the reinstall will solve the problem, but that's just my guess.

  9. Misato
    March 21, 2015 at 4:58 am

    What about just cleaning your mac to speed things up? I would be very hesitant to use Yasu or Onyx or any mac cleaning software. I once used Mac Cleaner, and it got rid of Windows system files I needed. I use Paralells and Windows 8 on my mac to run Windows software, and after I used Mac Cleaner once, Windows 8 was essentially made useless. What other way is there to clean your mac? It there anything like cleaning your registry, like with windows? If so, how do you do that on OS/X? Does OS/X even have a registry? This is my first Mac, and I switched from PC because I got tired of Microssoft's crap. When they stopped supporting XP, got rid of Outlook Express, and generally stopped being backwards compatible, I said enuff is enuff and switched to Apple. I just wish there was a simple way to clean OS/X without the risk of screwing up your operating system.

    • Justin Pot
      March 21, 2015 at 3:05 pm

      There is no "registry" on your Mac, and believe me: that's a good thing. I love Windows, but the registry is a mess that I hope is replaced by MS soon.

      I've never heard of Mac Cleaner, but I can tell you that Yasu won't touch anything to do with Windows setup – it serves a very specific function and doesn't do anything else. Other programs worth looking into include CCleaner for Mac.

  10. Daren Ridgway
    December 23, 2014 at 8:52 pm

    Hi, I just bought mine and have put on some apps, like google, photos and a few others and its suddenly 20gb emptier. So i thought it back to the day i bought it so i can do a complete time machine back up from scratch. or should i just do it from where i am now... all new to me.. if i reinstall will the SSD be completely back to scratch or have these past 2 days hidden on there somewhere?

    • Justin Pot
      December 26, 2014 at 3:00 pm

      Put simply: if you reinstall, everything is gone. But you might be better off trying to figure out what's taking up all of your space. Click the Apple at top-left, then"About This Mac". Click "Storage" and you should see a breakdown of what's taking up your space.

  11. Evilplankton
    September 6, 2014 at 11:05 pm

    I'm partly responsible for an office of about 80 people all running Mac hardware. I've rarely had to re-install OS X. Simply running "repair permissions" in the Disk Utility and rebooting/updating fixes almost every problem, even when re-purposing a laptop to a new user (and deleting the old profile). By the time a laptop gets old enough that it might need a re-install, there is usually some hardware failure so we toss it and buy a new one. Having FileVault enabled is usually the reason for the re-install.

    • Justin P
      September 8, 2014 at 5:20 pm

      Yeah, if you're not regularly installing and uninstalling software you'll rarely have issues, such as in a managed IT environment. I'm thinking an increasing number of Windows admins are having the same experience.

  12. Mike
    August 30, 2014 at 11:46 am

    Been using both OS's for longer than i care to admit. Re-install Windows every 6 months? You're joking right? If that were necessary, I'd never use it - no matter how much software runs on it. Windows98 was perhaps like that, because it was a memory leaker and software vendor installs could completely hose it. These days - certainly since Vista - takes a fair amount of carelessness to screw it up to the point of having to reinstall it.

    • Justin P
      August 31, 2014 at 9:47 pm

      I don't personally think you need to reinstall this often, but it's an often-repeated statement among some Windows users – to the extent that I thought Mac users might be curious.

      I was careful to point out this was probably more true of XP than it is of modern Windows incarnations. I've had a Windows computer running just fine for the last four years without issue.

  13. Woody House
    August 30, 2014 at 3:53 am

    Mavericks and Creative Cloud eat OSX memory like mad... upgrade using more RAM and get what we did... a screaming fast and enjoyable experience once again. Used third party 4 GIG ram sticks in addition to the 4 onboard for 12 out of a possible 16 gigs... gonna add another 4 to bump it up more... but it runs beautifully now.

    Give it a go.

  14. Jason
    August 30, 2014 at 3:03 am

    1. There is nothing true about your ridiculous statement that you must reinstall Windows every 6 months to a year. If you do, then it's because YOU are a moron.

    2. As a former Mac user who dumped Apple because their bloatware OS updates ruin every device they sell systematically, I'll say there's no reason to reinstall OSX because it just doesn't matter: Apple is gonna fuck you one way or the other.

    The vast majority of users go YEARS without reinstalling Windows, and that's never been more true than it is today. Post-Vista, every version of Windows has been smaller, leaner, lighter and faster than the version before, and more prone to staying that way.

    • Justin P
      August 31, 2014 at 9:44 pm

      1. I was pretty careful to say that lots of Windows users believe they need to reinstall every six months, not that I think this is actually true. I probably could have been more clear, so sorry.

      2. I do hate how OS X seems to become slower with every release, and you're right that Windows is actually getting better in this regard. Windows 8 is fast compared to 7, and OS X cannot claim the same thing. I'm hoping things get better.

    • James Bruce
      December 14, 2014 at 8:24 am

      The vast majority of Windows users don't really use their computer beyond a little Chrome browsing. For people like myself who regularly test software and hardware, things get corrupted beyond a point of being fixable, files collect and the system soon either breaks or slows to the point of being unusable. Happened this weekend; latest Oculus drivers mixed with latest AMD drivers managed to corrupt. Safe mode doesn't help, reinstalling both doesn't help – had to reinstall after 4 months of that particular Windows 7 installation. Anecdotally, I don't buy the theory that every version of Windows got leaner and more reliable - I'd go back to Windows 2000 in flash if I could. Now that was one very reliable OS, no matter how much you tried to break it.

      I have a 2009 iMac too; I've had to reinstall once in 5 years.

  15. Kello
    August 30, 2014 at 12:09 am

    It killed my Parallels Desktop VM and I have to reinstall windows VM!

  16. Harry
    August 29, 2014 at 11:05 pm

    I had an IT business for more than 10 years. Windows, going all the way back to Win 95/98 does not have to be reinstalled every year. Incidentally, I use a Mac for my personal computer just because I like it better.
    If you have to reinstall any common OS once a year you are certainly doing something wrong, especially with Win 7 or 8.
    With Windows it is easy to make an image of the system you have customized and simply restore it if something does get screwed up.
    With mac ( as was said) it is silly to reinstall. Clone a drive and boot to that if something goes wrong.
    Reinstalling an OS is Uber time consuming. A little time in the beginning saves a lot of time when TSHTF.

    • Justin P
      August 31, 2014 at 10:04 pm

      The point I was trying to make is that many Windows users like to say it's a good idea to install regularly, and then answer whether Mac users who hear this should be concerned. Looking at the comments here it's clear I didn't get that across, I think I might have to make an edit that makes it clear most Windows users also probably don't need to worry about this.

  17. John Williams
    August 29, 2014 at 9:06 pm

    I've been assured that Macs "just work" forever .... and if you do have a problem the Apple Store will just fix it .... now MUO is telling me thats not the case?
    Actually, it's a miracle that Apple even let you install software yourself, let alone the OS. Are you sure you don't just log on to iTunes every so often and it all just fixes itself?

    • Jason
      August 30, 2014 at 3:09 am

      Oh, it is absolutely untrue that Macs "just work" forever, and even more untrue that the Apple Store will "just fix it". I went all in with Apple a few years ago and it was the worst mistake of my computing life. Every OS upgrade on both OSX and iOS devices made it slower and slower, and Apple's response was always the same: "Leave it overnight and we'll look!" only to have it be exactly as it was before. Upon pointing this out, their response was a predictable, "Well the new one just came out, you should upgrade!"

      Eventually got tired of the bullshit, threw my hat in the ring with Surface Pro, recently got upgraded to a Pro 3 (for free, no less, after I uh, accidentally killed my first one with soaked hands), and haven't looked back. Up until I killed my original pro (which was entirely my fault, simple negligence), it was flawless for a full year. Now I have Pro 3 and it's hands down the best computer I've ever owned, bar none.

  18. Arsh Kapoor
    August 29, 2014 at 4:26 pm

    I have both Windows and mac after every 5-6 months windows require reinstallation while mac is running perfectly. But when it comes to softwares windows has wide range of it !

  19. Bud Mulqueeney
    August 29, 2014 at 4:05 pm

    A few things here....1) I always run an app called "CleanMyMac." 2) any problems, I periodically use my disk utility and the VERIFY button, then if necessary, use the VERIFY DISK PERMISSIONS, and if necessary, either run REPAIR, or REPAIR DISK PERMISSIONS.
    Never had to re-install OS X Mavericks.

    My current and major complaint with Apple is the INABILITY to easily remove/downgrade OS X Mavericks once installed. I've tried many times, with out luck and not being a Terminal user to use code, it's a troublesome aspect of Apple. Prior OS X's were NOT a problem, as I could then use BootCamp from Snow Leopard as an example, to install Windows to recover former disk copies on my floppies/ CD-RW discs . Sad that corporate computer makers LOVE to require additional payments for updated features of software one already has!!!!!!!!!!!

  20. Jan F
    August 29, 2014 at 1:23 pm

    It depends mostly on the type of user you are.

    If you test-install very little applications or only from the Mac App Store you'll probably be happy with your Mac even 6 years later after performing several OS X upgrades.

    If you install all sorts of Apps from all over the web you might have a better time re-installing after 3-4 years of accumulating dead Launch Daemons and Agents, unnecessary or incompatible Kernel extension etc.

    Those kind of issues are hardly ever seen by users (who looks at the system.log frequently?) and can be ignored. For most other errors you get on a Mac they are usually resolved by deleting the preferences file and/or repair permission on the system disk. But all in all they do add up, may cause issues here and there and mostly slow down your system with unnecessary tasks.

    Personally, I mostly use the same applications and tools with most of them not requiring me to restore their settings. Also I'm not really big on data. So I end up starting over every second or so OS X version (reinstall 10.7, upgrade 10.8, reinstall 10.9) and actually put my data back manually instead of Time Machine or so.

    • Justin P
      August 29, 2014 at 1:49 pm

      All great points, Jan. I, incidentally, do test a lot of software – maybe I need to consider installing Yosemite fresh this year.

  21. Anonymous
    August 29, 2014 at 12:22 pm

    If it is'nt broken don't fix it

  22. Nathanael
    August 29, 2014 at 11:54 am

    I was running the Yosemite beta when it wouldn't boot. So, I reinstalled, and it worked.

    • Justin P
      August 29, 2014 at 1:12 pm

      I guess I should have added "installing a beta OS" to the list, eh?

    • Nathanael
      August 29, 2014 at 1:42 pm

      I know you mentioned downgrading from a beta, but not fixing a beta.

  23. applegenius
    August 28, 2014 at 9:59 pm

    Most people install Windows on it.

  24. Jimmy
    August 28, 2014 at 9:09 pm

    I had a 2011 MBP that went from SL-->L-->ML-->Mavericks and started doing some very strange things on boot. Wasn't until I dual booted SL for old recording software I noticed it didn't do it. Clean install of Mavericks was the only way forward. Good as new and allowed me a chance to clean up programs I had installed by only reinstalling on an as-needed basis.

  25. JustReboot
    August 28, 2014 at 5:45 pm

    I just reinstalled 2x (once after 10.10 install, and the other because things were really borked). I haven't tried Yasu before, so I'll remember to try that in the future. Typically, just to keep things clean, I'll do a fresh install-rebuild about every 6-9 months. (That goes for my Windows machines too.)

  26. Android KopyKat
    August 28, 2014 at 5:28 pm

    i just carbon copy clone my fresh install of os x so i dont have to ever reinstall it again.

    • Archie
      March 9, 2015 at 3:55 pm

      How does that work?

    • Justin Pot
      March 9, 2015 at 4:22 pm

      Carbon Copy Cloner makes a full copy of your hard drive, which you can restore using Disk Utility instead of reinstalling.