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How to Migrate to a New Mac Without Carrying the Junk Over

Set up your new Mac with everything that matters and none of the cruft. Use Migration Assistant strategically to leave old caches and clutter behind.

9 min read

You bought a new Mac. The temptation is to plug it into your old one, run Migration Assistant, walk away, and come back to a perfect clone. That works — and it’s also how you end up with a brand new MacBook that has the same 80 GB of old caches, leftover apps from 2021, and weird Library folder bloat you’ve been meaning to deal with for years.

There’s a smarter way. It takes a little more thought up front and saves you from paying for storage you don’t need.

Decide what you actually want to bring over

Before you connect any cables, list what you need on the new Mac. The categories Migration Assistant offers:

  1. Applications — third-party apps from /Applications
  2. Documents and Data — your home folder
  3. Computer & Network Settings — Wi-Fi, Bluetooth, system preferences
  4. Users — your account and any others on the old Mac

Bring all four if you want a clone. Skip categories selectively if you want a fresh start in some areas.

The honest answer for most people: bring Documents and Data, bring Users, skip Applications, skip System Settings. Reinstall apps cleanly from current versions. Reset settings on the new Mac to current defaults. This adds 30-60 minutes of work and leaves behind years of accumulated config drift.

Clean the old Mac first

This is the step everyone skips and shouldn’t. The cleaner your source, the faster the migration, and the cleaner the destination.

On the old Mac, before connecting anything:

  1. Empty the Trash. Migration Assistant doesn’t always copy Trash, but local snapshots might.
  2. Clear obvious bloat. ~/Downloads folders from 2022, old .dmg installers, projects you’ll never open again.
  3. Uninstall apps you don’t use. Drag to Trash + clear preferences and support files (or use a tool that does it cleanly).
  4. Run a Time Machine backup. Insurance — if something goes wrong in migration, you have a fallback.
  5. Sign out of services. iCloud, Adobe Creative Cloud, Microsoft 365, anything with seat-based licensing. Many of these need a sign-out before they’ll activate on the new Mac.

A typical 5-year-old MacBook has 30-80 GB of accumulated junk that has zero value. Clearing it before migration cuts the transfer time and leaves you with a new Mac that’s actually new.

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Choose your migration method

Migration Assistant supports three sources:

  1. Mac to Mac (direct) — Thunderbolt cable, Wi-Fi, or Ethernet
  2. Time Machine backup — point at your backup drive
  3. Startup disk — point at a CCC clone or external boot drive

Speed comparison for 500 GB of data:

  • Thunderbolt 3/4 cable: 2-3 hours
  • Wired Ethernet (gigabit): 4-5 hours
  • USB-C SSD with Time Machine backup: 3-4 hours
  • Wi-Fi 6: 8-12 hours (or longer; expect drops)
  • Wi-Fi older standards: don’t bother

The fastest, most reliable method is Thunderbolt cable directly between Macs. Buy a Thunderbolt 4 cable ($30) for one-time use and return it if needed. The hour you save vs. Wi-Fi is worth it.

If you don’t have the option to plug Macs together, use Time Machine. Make a fresh, complete backup the day before, then plug the drive into the new Mac during Setup Assistant.

Run Migration Assistant the right way

When you first boot the new Mac, Setup Assistant offers Migration Assistant. You can also run Migration Assistant later from Applications → Utilities → Migration Assistant.

If you skipped it during setup, the manual flow:

  1. On the new Mac, open Applications → Utilities → Migration Assistant.
  2. Choose From a Mac, Time Machine backup, or Startup disk.
  3. On the old Mac (if Mac-to-Mac), open Migration Assistant and choose To another Mac.
  4. Wait for the new Mac to find the old Mac and confirm a security code.
  5. Pick what to transfer. Uncheck what you don’t want.
  6. Confirm and wait.

The migration runs in the foreground. Don’t close the lid, don’t put either Mac to sleep. If the lid closes mid-migration on a MacBook, the transfer pauses and sometimes fails. Plug both into power.

Time estimates from Migration Assistant are notoriously wrong. A “30 minutes remaining” estimate often means 3 hours. Plan for it to take longer than you think and don’t interrupt it.

What Migration Assistant misses

Even a “complete” migration leaves some things behind:

  • App-specific licenses — many apps need to be reactivated even after migration
  • Browser sessions — you’ll be signed out of websites
  • Some app preferences — apps with cloud-stored settings will re-sync; others lose state
  • Two-factor codes — Authy, 1Password, Google Authenticator. Set these up before migrating to avoid getting locked out.
  • SSH keys’ agent state — keys are copied but you may need to re-add them to the agent
  • Homebrew, npm, gems — the binaries copy, but path and permissions sometimes need fixing

Plan for an hour of “I’m signed out of everything” after migration. Have your password manager ready.

Tip: Don't sign out of iMessage on the old Mac before migrating. The migration carries iMessage state. If you sign out, the new Mac has to re-register, which sometimes fails on the first try.

The “fresh start with selective import” approach

If you want a truly clean new Mac, don’t run Migration Assistant at all. Instead:

  1. Set up the new Mac as a new user during Setup Assistant.
  2. Sign into iCloud — Calendar, Contacts, Reminders, Photos all sync automatically.
  3. Sign into other cloud services for documents.
  4. Reinstall apps from their current installers (or Mac App Store, or Homebrew).
  5. Manually copy specific folders from the old Mac:
    • ~/Documents/your-actual-projects/
    • ~/Pictures/Photos Library.photoslibrary (if not in iCloud)
    • ~/Music/Music/Media (if not in Apple Music cloud)
    • Specific config files: ~/.ssh/, ~/.gitconfig, ~/.zshrc

This takes a Saturday. The result is a Mac with literally none of your old cruft.

It’s overkill for most people but worth considering when you’ve been on the same Mac for 5+ years and the old setup is genuinely a mess.

Migration with /Users/Shared

Some people store working files in /Users/Shared so multiple users on a Mac can access them. Migration Assistant copies this folder, but it sometimes preserves wrong permissions on the destination. After migration, check:

ls -la /Users/Shared

If files there are owned by your old user UID rather than the matching new user, fix with:

sudo chown -R $(whoami):staff /Users/Shared/your-folder

Apps you should reinstall, not migrate

Some apps survive migration poorly. Reinstall fresh:

  • Anti-virus / security tools — they often have device-specific licenses or kernel extensions that need fresh install
  • VPN clients — system extensions may not transfer cleanly
  • Pro audio plugins — many have machine-specific authorization
  • Adobe Creative Cloud — sign out on old Mac, install fresh on new Mac
  • Logic Pro / Final Cut Pro — Apple’s apps sometimes need to re-download content libraries (10+ GB each)
  • Microsoft 365 — sign out before migration; it’ll handle reactivation cleanly

For everything else (Slack, Notion, browsers, editors, dev tools), migration usually works.

After the migration: clean up the inheritance

Once migration finishes and you’ve signed back into everything, run a cleanup pass on the new Mac:

  1. Check disk usage: System Settings → General → Storage. If “Other” or “System Data” is over 30 GB, there’s leftover junk.
  2. Review Login Items: System Settings → General → Login Items. Old startup items get carried over and slow boots.
  3. Check Privacy & Security: System Settings → Privacy & Security. Old permissions for apps you no longer use clutter the lists.
  4. Look at ~/Library/Containers: contains data for sandboxed apps. Some of this is tied to apps you migrated but may not have reinstalled.
  5. Check ~/Library/Application Support: same as above for non-sandboxed apps.

A new Mac after Migration Assistant is technically usable, but it’s not “clean” — it’s the old Mac wearing a new chassis. Take 30 minutes after migration to clear what you don’t need.

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Why a clean migration matters more than ever

New Macs ship with smaller default storage tiers than they used to (256 GB base on lots of M-series MacBooks). If you migrate a 400 GB old Mac to a new 256 GB Mac, you’re stuck with iCloud “Optimize Mac Storage” or external drives from day one.

Cleaning the old Mac before migration often saves enough space to fit comfortably on the new tier. A 400 GB Mac that’s actually 200 GB of work plus 200 GB of accumulated cruft becomes a 200 GB Mac that fits on the new 256 GB drive with breathing room.

Sweep helps specifically with the categories that aren’t yours — they’re the byproducts of using your Mac:

  • Caches that regenerate (so they’re never restored anyway)
  • Old installer disk images
  • App leftovers from drag-to-Trash removals
  • Localizations for languages you don’t use
  • Old iOS device backups
  • Local APFS snapshots eating space

It’s not a backup — Time Machine handles that. It’s the broom that sweeps out what doesn’t belong in the next house.

A migration weekend plan

For someone moving from a 5-year-old MacBook Pro to a new MacBook:

Friday night:

  • Run a fresh Time Machine backup on the old Mac
  • Clean up the old Mac (remove 30-60 GB of obvious junk)
  • Sign out of major services (Adobe, Microsoft, anything seat-licensed)

Saturday morning:

  • Unbox new Mac
  • Run Setup Assistant
  • Choose Migration Assistant, point at old Mac via Thunderbolt cable
  • Wait 2-3 hours

Saturday afternoon:

  • Sign into iCloud, Apple ID
  • Reinstall any apps that didn’t migrate cleanly
  • Set up Touch ID, password manager, dev environment
  • Test that critical apps work

Sunday:

  • Use the new Mac normally; note anything broken
  • Clean up “Login Items” and Privacy permissions
  • Run another Time Machine backup of the new Mac to a different drive
  • Wipe old Mac if selling, or set aside for emergency fallback

That’s a realistic two-day window. Migration is rarely a 30-minute task. Plan accordingly and you won’t be cursing your new Mac on Sunday night because nothing works.

The new Mac you actually want is one that does today’s work without yesterday’s baggage. Migration Assistant gets you partway there. The rest is on you.

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