macOS Migration Assistant Error — Transfer Failed Fix

What Does This Error Mean?

macOS Migration Assistant errors occur when the transfer of data between Macs or from a Time Machine backup is interrupted or fails. Common symptoms include the transfer stopping partway through, showing a progress bar that freezes, or a message saying 'Transfer failed.' This is usually caused by a weak Wi-Fi connection, a corrupted backup, incompatible macOS versions, or a problem on the source drive.

Affected Models

MacBook Air
MacBook Pro
iMac
Mac Mini
Mac Pro
Mac Studio

Common Causes

The Wi-Fi connection between the two Macs dropped during the transfer
The Time Machine backup being used as the source is corrupted or incomplete
The source Mac has a failing drive that cannot read files reliably
The macOS versions on the two Macs are too far apart for direct migration
A large number of files or very large file sizes caused the transfer to time out

How to Fix It

Switch to a wired Thunderbolt or USB connection. Connect both Macs with a Thunderbolt or USB-C cable. In Migration Assistant, choose to transfer from 'From a Mac, Time Machine backup, or startup disk' and select the wired connection.

A wired connection is dramatically faster and more reliable than Wi-Fi for large migrations. Most transfer failures on Wi-Fi succeed immediately over a cable.
Update macOS on both Macs before migrating. On both machines, go to System Settings > General > Software Update and install all available updates.

Migration Assistant works most reliably when both Macs are running the same or close macOS versions. Large version gaps can cause compatibility errors.
Verify the Time Machine backup (if migrating from a backup). Connect the Time Machine drive, open Disk Utility, select the backup drive, and click First Aid to check for errors.

A corrupted Time Machine backup will fail partway through migration. Fix disk errors first, or use a different backup if available.
Restart both Macs and try again. Quit Migration Assistant on both machines, restart both Macs, and open Migration Assistant fresh.

A clean start clears any stuck network sessions or cached state that may have caused the previous failure.
Try migrating in smaller pieces. Instead of migrating everything at once, choose specific categories — Applications first, then Documents, then other data — to see which category causes the failure.

If one specific folder or app is corrupted, selectively excluding it allows the rest of the migration to succeed.

When to Call a Professional

If the source drive is failing and Migration Assistant cannot read files from it, a data recovery specialist may be able to retrieve your data. Act quickly — a failing drive can stop working entirely with no warning.

Frequently Asked Questions

How long should Migration Assistant take?

Migration time depends entirely on how much data you are transferring and how you are connected. Over a wired Thunderbolt cable, expect roughly 1–3 hours for 100–200 GB of data. Over Wi-Fi, the same transfer could take 6–12 hours or more. For very large transfers (500 GB+), use a wired cable and plan for an overnight transfer.

Can I still use my old Mac after migrating?

Yes. Migration Assistant copies your data — it does not delete it from the source Mac. Your old Mac remains exactly as it was. Once you confirm the new Mac has everything you need, you can erase the old Mac separately.

Migration finished but some apps are missing. What happened?

Some apps cannot be migrated directly because they use licensing systems that tie them to a specific Mac. Examples include some Adobe apps and certain subscription software. You will need to re-download and re-activate those apps on the new Mac using your existing license or subscription account.