Apple Migration Assistant: what it moves and what it misses

Apple Migration Assistant has one job and does it well, which is why the disappointment afterwards is so consistent. The files arrive. The apps arrive. Then a week of small repairs begins: a mail account asking to be set up again, bookmarks sitting in a browser nobody uses, every web app signed out, a Wi-Fi network that has to be typed in by hand.

None of that is a fault in the tool. It is the difference between what a migration tool is designed to carry and what a working setup actually consists of. Knowing that boundary before starting turns a week of surprises into a short list written down in advance. What follows states what Migration Assistant moves, where each category lands, the one decision that cannot be undone afterwards, and what has to be rebuilt by hand regardless.

What Migration Assistant actually is

Migration Assistant ships with macOS and lives in the Utilities folder, though on a Mac being set up for the first time it appears as part of the setup assistant instead. It reads from four sources: another Mac, a Time Machine backup, another startup disk, or a Windows PC.

Apple states plainly that it transfers documents, apps, user accounts and settings, that it does not delete anything from the old machine, and that it does not replace macOS on the new one. Both points matter. The old Mac remains usable and unchanged, so there is no rush to wipe it, and the new Mac keeps its own macOS version, so there is no risk of an older system being dragged forward.

The macOS versions on the two Macs do not need to match. Apple's guidance is to update both before starting, but a newer Mac reading from an older one is the normal case rather than an exception.

For a PC, the transfer needs a separate download called Windows Migration Assistant, and the correct version depends on the macOS release on the receiving Mac. Version 3.2.0.0 covers macOS 27, Tahoe 26, Sequoia 15 and Sonoma 14, and requires Windows 10 or later. Versions 2.4.5.0 and 2.3.1.0 exist for Ventura 13, Monterey 12 and Big Sur 11, and support Windows 7 or later. Downloading the wrong one is the most common way to lose an afternoon before the transfer even begins.

Preparing both machines, and running it

The preparation list is short, and skipping any of it is the usual cause of a transfer that stalls at ninety percent.

Update macOS on both Macs, or Windows and macOS for a PC transfer. Turn on Wi-Fi and Bluetooth, and put the two machines near each other. Close every application. Then turn off antivirus, firewall and VPN software, because all three interfere with the direct connection the two machines negotiate. For macOS 13 or earlier on a PC transfer, Apple specifies an Ethernet cable or the same network. For a Mac running OS X El Capitan or earlier, both Macs need to be on the same Wi-Fi network.

On the receiving Mac, open Migration Assistant and choose either from a Mac, Time Machine or startup disk, or from a Windows PC. On the old Mac, open Migration Assistant and choose to transfer to another Mac. On a PC, open the downloaded Windows Migration Assistant and type in the code shown on the Mac. Security codes are shown on both sides and are meant to be compared before continuing.

The receiving Mac then calculates storage, which on a large disk takes several minutes and looks stuck. After that comes the list of data categories to include, then the passwords, then the transfer itself. Apple's own guidance is that a large transfer can take hours, so this is a task to start in the evening rather than half an hour before it is needed.

What arrives from a PC, and where it lands

A Mac to Mac transfer keeps the shape of the original, so the surprises are few. A PC transfer rearranges everything, and the destinations are worth reading before rather than after.

On the PC	Where it lands on the Mac
Email and email settings from Outlook and Windows Mail	Mail
Contacts from People, Outlook, and the Contacts folder	Contacts
Appointments from Calendar and Outlook	Calendar
Tasks from Outlook, on macOS 13 or later	Reminders
Homepage and bookmarks from Chrome, Edge, Firefox, Internet Explorer and Safari	Safari
Music library, podcasts, audiobooks, movies and TV shows	Music, Podcasts, Books and TV
Documents and other files from the home directory	Home folder
Photos	Home folder, to be added to Photos by hand
Custom desktop pictures, language and location settings	System Settings
Non system files from C: and other drives	Shared folder

Two rows in that table cause most of the confusion. Bookmarks from every browser on the PC land in Safari, which for someone who has used Chrome for a decade means the bookmarks are technically present and practically invisible. They can be exported from Safari and imported into another browser afterwards, but nobody expects to have to. And photos land in the home folder rather than inside the Photos library, so the Photos app looks empty until they are imported manually.

The user account decision is the irreversible one

Everything else in a migration can be repeated. The account structure cannot, without starting the new Mac over.

Migration Assistant asks what to do when an account name on the source already exists on the destination. The options are to replace the existing account or to rename the incoming one. Replacing removes what is already there. Renaming leaves two accounts on the Mac, each with its own home folder, which is the situation people describe later as the new Mac having their files in two places.

The cleanest outcome on a brand new Mac is to run Migration Assistant from the setup assistant before creating any account of your own, so there is nothing to collide with. If the Mac has already been set up, the conflict is unavoidable and the choice has to be deliberate.

Passwords need attention at the same moment. Apple's instructions are to set passwords for administrator accounts and to note the temporary passwords generated for standard accounts, because those temporary passwords are what the first login uses. Nothing shows them again later. Writing them down at that screen takes ten seconds and prevents an account that cannot be opened.

What it misses

The gaps are specific and documented, which makes them easy to plan around once listed.

Passwords are the largest one. Keychains transfer when a Mac is migrated through the setup assistant, but Apple states that passwords stored in Local Items or in the iCloud Keychain cannot be copied across, and that the way to carry those is to sign in to the same Apple Account on the new Mac and set up iCloud Keychain there. For a PC transfer, network settings and passwords are not transferred at all, so every saved Wi-Fi network has to be entered again.

Email accounts arrive, but the configuration inside a third party mail client generally does not, and Apple notes that email requires reconfiguration in the email app after transfer. Applications arrive as files, which is not the same as arriving ready to use: anything tied to a licence key, a hardware identifier or a per machine activation asks to be authorised again, and the licence details live in the vendor's account rather than on the disk.

Two smaller gaps are worth noting because they look like failures rather than design. Non system files from the C: drive and any other drives on a PC land in a Shared folder rather than in the home folder, and reaching them needs administrator access, so they can appear to have been skipped. And on a PC transfer, tasks from Outlook only move to Reminders when the receiving Mac runs macOS 13 or later, which means an older Mac silently leaves them behind.

The largest category is the one nobody thinks to list, because it does not live on the old machine at all. Every browser session, every signed in web app, every second account on the same service: none of it is a file, so none of it moves. That is not an oversight in Migration Assistant. There is nothing on the disk for it to copy.

When it fails partway

A transfer that stops or errors out is usually a disk problem on the source rather than a fault in the transfer itself.

For a PC, Apple's documented step is the check disk utility. Right click Start, choose Run, type cmd and press Enter, then run chkdsk. If problems are reported, run chkdsk drive: /F with C as the drive, restart, and repeat until it reports nothing. Apple's guidance is explicit about what to do if that does not clear it: use an external storage device or file sharing to copy the important files across instead of persisting with the transfer.

That fallback is worth taking earlier than most people do. A manual copy of the documents folder is slower and less tidy, but it finishes, and it never leaves a half migrated account behind. Disk Utility's First Aid serves the same diagnostic purpose on a Mac to Mac transfer that refuses to complete.

Three other causes account for most stalls. Security software that was disabled and then re enabled by an update part way through will cut the connection, so it is worth confirming it is still off rather than assuming. A Mac that goes to sleep stops the transfer, which is why the power settings are worth checking before an overnight run. And a transfer attempted over a congested Wi-Fi network can slow to the point of looking frozen, which a cable between the two machines removes as a variable.

There is also a decision to make when a transfer has to be abandoned halfway. Reverting the new Mac to a clean state and starting again is tedious but predictable. Continuing on top of a partial migration leaves duplicated folders and permissions that are difficult to reason about later. On a machine that will be used for years, the clean restart is usually the cheaper of the two.

The layer no migration tool carries

Once the files are in place, the remaining work is almost entirely sign ins. A work Gmail, a personal Gmail, Slack, Notion, a design tool, a project tracker, a support inbox. Each one is a page in a browser rather than an app on the disk, each needs a password and a second factor, and for anyone holding two accounts on the same service the process has to be repeated with profiles or private windows.

This is the part that makes a new Mac feel unfinished for a fortnight, and it repeats in full at every hardware change. Reducing it means holding that layer somewhere portable. A browser organised around apps rather than tabs gives each web app its own window and its own cookie container, so several accounts on one service stay signed in side by side, and the arrangement itself becomes a thing that can be described and rebuilt rather than rediscovered. Each workspace holds its own session, the feature list covers what is kept per app, and the supported apps page is the place to check that the specific services in question are handled.

What to do first

Before starting the transfer, write down two lists: the applications that will ask for a licence key, and the web services that will ask for a password. Those two lists are the week of small repairs, made visible in advance and finished in an afternoon instead. If the second list is the longer of the two, the layer worth changing is the browser, and SpaceDeck is built for exactly that layer.