The storage audit nobody does after an upgrade.

What does Migration Assistant transfer to a new Mac?

Apple says Migration Assistant transfers documents, apps, user accounts, and settings from one Mac to another. Its selection screen lets you choose categories and, in some categories, specific items such as an account's Downloads, Movies, Desktop, documents, and pictures.

Before you start the transfer, Migration Assistant calculates how much storage is used by the information it found, including applications, user accounts, files, folders, and settings. Treat this as an estimate of selected source data, not a promise that the same amount will appear as used on the new Mac: apps, accounts, system versions, and storage accounting can differ.

Apple's documentation does not specify which caches, hidden files, or duplicate files are copied or skipped in every case. This guide does not assume that Migration Assistant cleans those items or transfers all of them. Inspect the result on your Mac.

Read more: Apple Support: transfer to a new Mac with Migration Assistant · Apple Support: transfer information to Mac from another computer or device

Does Migration Assistant erase the old Mac?

No. Apple says Migration Assistant does not delete information from the old Mac or replace macOS on the new Mac. That means the source Mac can remain available while you verify the destination, but it is not a substitute for a separate backup.

• Keep the old Mac unchanged while you check important files, projects, photos, passwords, and apps on the new Mac.
• Read the migration summary. Apple says it appears when issues are found, such as documents that could not transfer or incompatible software.
• If you used iCloud Photos, iCloud Drive, or another sync service, later changes can sync between devices. The old Mac may not be an independent copy of synced data.
• Make a separate backup of data you need before erasing, selling, or giving away the old Mac. Follow Apple's current erase-and-transfer instructions only after verification.

Large transfers can take hours and may seem to pause occasionally, according to Apple. When the transfer finishes, allow the new Mac to restart and sign in to the migrated account before checking the result.

Read more: Apple Support: transfer to a new Mac with Migration Assistant · Apple Support: what to do before you sell, give away, trade in, or recycle your Mac · Apple Support: iCloud not freeing Mac space? Photos storage explained

Can a second account or retained user data take extra space?

It can. If an account with the same name already exists on the new Mac, Migration Assistant may let you replace it or rename the incoming account. Apple also says you may be able to keep a copy of replaced account data in Deleted Users.

• If you choose to keep replaced account data, review it later before removing anything. Confirm that the migrated account has the files you expect and that the retained copy is no longer needed.
• If you rename the incoming account, Apple says both accounts remain on the Mac so you can log in to them separately. Review the account list and storage before deleting either account.
• Apple's Mac storage guide also recommends checking the Users folder for data that remains after a user account has been deleted. Do not remove a folder just because its name is unfamiliar; first identify which account or files depend on it.

Migration Assistant transfers email, but Apple notes that you might need to set up your email account again in the mail app to access it. Treat any setup or sign-in issue as something to resolve before erasing the source Mac.

Read more: Apple Support: transfer to a new Mac with Migration Assistant · Apple Support: change Storage settings on Mac

How do you check storage on the new Mac?

Start with Apple's built-in Storage view, then inspect large folders that belong to your user account. The category totals help locate likely areas; they are not a complete explanation of every byte on an APFS disk.

1. Open Apple menu > System Settings > General > Storage. Review the categories and use an Info button where Apple offers one to inspect items.
2. Check Photos if you migrated a large System Photo Library. Apple's Storage guide says the Photos category contains the System Photo Library.
3. Open Documents and File Browser to inspect large files and the storage used by folders. Storage categories vary with the apps and files on the Mac.
4. Compare the displayed free and available storage carefully. Apple defines free space as physically open space; available space can also include purgeable data that macOS may reclaim.
5. Measure folders you recognize before deciding what to keep. Do not delete from System Data, macOS, or inside managed app libraries based only on a category total.

If the new Mac uses iCloud Photos or iCloud Drive, check whether items are downloaded or optimized before interpreting a local size. Our iCloud storage guide explains those settings and the difference between local removal and deleting a synced item.

Read more: Apple Support: change Storage settings on Mac · Apple Support: find and delete files on Mac · Apple Support: get detailed information about a disk · Apple Support: iCloud not freeing Mac space? Photos storage explained

Which read-only commands can help find large folders?

These commands list folder sizes or matching file paths. They do not remove files, determine whether a file is safe to delete, or verify that Migration Assistant copied it correctly. Run them from Terminal without adding sudo.

Compare the sizes of common folders in your home directory:

List the largest items directly inside your home folder, including hidden folders such as Library when permissions allow:

Find installer and archive files larger than 100 MB in Downloads, Desktop, and Documents:

A folder that does not exist, privacy permissions, cloud-only files, or unreadable locations can affect the output. A quiet result does not prove the Mac contains no large files. These commands are read-only; use Finder or the app that owns a file to review it before removing it.

Read more: Apple Support: change Storage settings on Mac · Apple Support: find and delete files on Mac · macOS 26.7 man page: du · macOS 26.7 man page: find · macOS 26.7 man page: sort

What should you review before removing migrated files?

Treat a large size as a reason to inspect a file, not proof that it is disposable. Verify the app or project works, identify whether a file is original or generated, and make a recoverable copy before you remove anything important.

• Installers: after confirming the installed app opens and you can retrieve the installer again, an old .dmg or .pkg may be a cleanup candidate. Keep offline installers or license files you still need.
• Exports: names such as final, final-2, or export are clues only. Compare file contents before treating files as identical. Our iPhone video guide explains hash comparison and its limits.
• Projects: open active projects and check linked media before archiving. For Final Cut Pro libraries and source footage, use the separate video project storage guide.
• Applications: Apple says incompatible apps or apps with newer versions already installed may not transfer or may not be usable. Check the developer's current version and license before removing or reinstalling an app.
• Deleted Users: if you chose to retain replaced account data, check what the retained copy contains and whether the migrated account is complete before removing it.

Use the Trash first and keep it until you have worked on the new Mac for a while. See how to decide whether a Mac file is safe to delete for a slower review process. Avoid broad cleanup commands and never erase the old Mac just to reclaim new-Mac storage.

Read more: Apple Support: transfer to a new Mac with Migration Assistant · Apple Support: find and delete files on Mac · Diskfern: decide whether a Mac file is safe to delete · Diskfern: video files and Final Cut Pro storage

Where Diskfern fits after a Mac migration

A local storage map can help you find large folders and files after migration. It cannot tell whether Migration Assistant transferred everything, whether an app is compatible, or whether a file is safe to remove.

Use Diskfern to locate local storage for review, then open files and apps to verify them. For a manual approach, see find large files on Mac.

Read more: Diskfern: find large files on Mac