Slow Copying:

1. •The first backup after an OSX upgrade will be very slow.  It will be even slower if Spotlight is still indexing.   Click the Spotlight icon at the right of your menubar;  if it shows indexing in progress, backups will be very slow.  It's often best to cancel the backup, and try again later when Spotlight is done.
   

2. •Especially on Mountain Lion, the first backup after an OSX upgrade may appear to "stall" for several minutes or more, but then complete normally, so allow it plenty of time.
   

3. •If this is your first backup after upgrading from a previous version of OSX;  or on a new Mac after selecting the Inherit or Re-Use Backup option per item #B5 or doing that manually, per item #B6;  or after doing a full restore, the backup may be a full backup of the new Mac.  Or, Time Machine may say it's going to do a full backup (and delete a lot of old backups if necessary), and then appear to be backing-up very, very slowly.  After a long time, when it doesn't seem anywhere near done, it may complete normally, having actually done only an incremental backup. 
   

4. •The first backup after installing a fresh version of OSX over a previous one (but not a "clean" install), may also say it's going to do a large backup (and delete a lot of old ones if necessary), and then appear to be backing-up very, very slowly.  After a long time, when it doesn't seem anywhere near done, it may complete normally, having actually done only a small backup.
   

5. •The first backup after one that failed or was cancelled may appear to be running very slowly, while Time Machine "recovers" the partial ".inProgress" file from the previous one.  Give it a long time before deciding there's a problem.
   

6. •The first backup after removing certain exclusions, especially System Folders and/or Applications, can appear to be extremely slow, as they involve tens of thousands of mostly very small files.  It may also seem to report that it’s reached the amount to be backed-up, but then the amount will increase (often very slowly).
   

7. •If you're running Lion, and haven't installed the 10.7.5 Supplemental Update, try that first.  (If you're not sure, it's build 11G63.  See What version of OSX do I  have? for your build number.)
   

If none of those explain the problem, get the Time Machine Buddy messages (see item #A1).

If it shows "deep event scan" or ". . . node requires deep traversal" message(s) it may not be "hung" at all. See item #A6 for an explanation of that.

If it shows "Waiting for index to be ready" and/or "Bulk setting Spotlight attributes failed" messages, there may be a problem with your Time Machine drive, or difficulty communicating with it. Unfortunately, any of a number of things may cause this.

1. •If you're running Snow Leopard, and the messages show many thousands of files being backed-up but very little space used, check your ~/Library/Preferences and ~/Library/Preferences/ByHost folders for thousands of files with a size of zero bytes and various 4-character suffixes after the .plist in the name (especially named com.apple.iTunes.plist.xxxx).   Delete them.
   

And sometimes your backups may be slow even without those messages.

If nothing here helps, try the things in the green box:

1. •  All backup destinations:
   

1. 1.If you have any anti-virus apps, exclude your Time Machine drive from it.  Better, turn it off at least temporarily.  Better yet, uninstall any such apps, except the free ClamXav or Sophos Anti-Virus for Mac Home Edition.  (Don't just delete them -- use the uninstaller supplied by the maker). 
   

2. 2.If there's anything drive besides backups on your Time Machine drive (not a good idea: see Time Machine FAQ #3), exclude it, at least temporarily, from Spotlight (System Preferences > Spotlight > Privacy).   (Effective with Lion, you'll get a message that you can't exclude your backups, but that anything else on the drive/partition will be excluded.)
   

3. 3.Repair your backups (and any external drives being backed-up), and Verify your internal HD, per item #A5.
   

4. 4.Repair Disk Permissions on your OSX drive, per #5 in Using Disk Utility.
   

5. 5.Relaunch the Finder (press Alt/Option+Cmd+Escape, select Finder, and click Relaunch.
   

1. •If backing-up via a network:
   

6. 6.Check and/or change your Computer, etc. names if needed, per item #C9.
   

7. 7.Try connecting via Ethernet (then turn Airport off to be sure it's really switched).  
   

8. To be sure Ethernet is used when both Airport and Ethernet are ON, go to System Preferences > Network, click the "gear" icon at the bottom of the list, select Set Service Order, then drag Ethernet above Airport.  To be sure it's using Ethernet, turn WIFI off.
   

9. Try a different Ethernet cable, ports, and combinations of the two.  Try moving your backup destination farther from your modem.
   

8. 8.If connected via WIFI (and Ethernet backups work well):
   

1. a.Move your Mac closer to the TC, Airport, or router.  Note that Airport Extremes and Time Capsules broadcast mostly up and out, so be sure it's not higher than your Mac.
   

2. b.Download the free  iStumbler  app to examine the strength of your connection.
   

3. c.Look for interference with another wireless device, cordless phone, microwave oven, etc.  Turn them off temporarily;  if you find an offender, move it farther away.  See  AirPort and Bluetooth: Potential sources of wireless interference  for more.
   

4. d.Try different WIFI channels.
   

1. •If backing-up to an external hard drive:
   

9. 9.At least temporarily, de-select Put the hard disk(s) to sleep ... in System Preferences > Energy Saver.  (Not all external drives respond to that setting, though.)
   

10. 10.Be sure the drive is connected directly to your Mac (no hubs or daisy-chaining, at least temporarily;  and not the USB port on the keyboard, as some are USB 1.0).
    

11. 11.Be sure all connections are snug and secure.  Try different port(s), cable(s), and combinations of them (a plug that works fine in one port may not make good contact in another). 
    

12. 12.If you have a multi-interface drive (such as USB and FireWire), try the other interface.
    

13. 13.See if your drive has an automatic sleep or "spin down" feature you can disable.
    

14. 14.Check the maker's web site for any driver or firmware updates.
    

1. •If nothing seems to help:
   

15. 15.There are some applications that can, in some circumstances, cause large and/or slow backups.  See Troubleshooting item #D8 for details.
    

16. 16.A (very) few folks have reported that starting in Safe Mode, then rebooting normally, helps (the next backup may be quite slow, but then speeds return to normal).
    

17. 17.Something in your installation of OSX may be damaged.  You might try installing the "combo" update, per Installing the ''combo'' update and/or Reinstalling OSX.  If that doesn't help, you might try installing a fresh copy of OSX, per the same article.
    

If nothing helps, your drive may be failing (they all do, sooner or later).

Repeated Indexing messages

If you're running Lion, and haven't installed the 10.7.5 Supplemental Update, try that first.  (If you're not sure, it's build 11G63.  See What version of OSX do I  have? for your build number.)

Especially if you're on Lion 10.7.x or later, if you see many "indexing" messages via the widget above, on subsequent backups, the index may be corrupted.  Usually, Repairing your backups per section #A5 will fix it, but not always.  If not, you may need to delete it.

First, download the Tinker Tool app, per section #A3.  Follow the instructions there to show invisible files (as noted there, reverse the procedure when done).

IF YOUR BACKUPS ARE LOCAL (on an internal or directly-connected external HD:

Open the Time Machine drive/partition via the Finder.  At the top level you'll find a folder named .Spotlight-V100.  Delete it (you'll have to enter your Admin password), and empty the trash (which may take quite a while).  Do not touch anything else.

Run a backup.  The first one will take quite a while, as the index must be recreated and the backups indexed, but thereafter backups should run normally.

IF YOUR BACKUPS ARE ON A NETWORK such as a Time Capsule:

This may take a while, so connect via Ethernet if at all possible.  It will be 2-3 times faster than via WIFI.

Via the Finder, locate the sparse bundle, and double-click it to mount the disk image inside it.  It will appear on your desktop or Finder sidebar, (that may take a moment) and is usually named "Time Machine Backups"  but might be "Backup of  <computer name>".  Double-click it to open it.  Inside it you'll find a folder named .Spotlight-V100.  Delete it (you'll have to enter your Admin password) and empty the trash (which may take quite a while).  Do not touch anything else.

Eject the disk image and run a backup.  The first one will take quite a while, as the index must be recreated and the backups indexed, so remain connected via Ethernet if at all possible.  Thereafter backups should run normally.

Finishing Backup or Cleaning Up

This is usually done at the end of each backup, but if the Preparing phase determines there isn't enough room for the new backup, it will be done first.

1. •On every backup, Time Machine deletes any "expired" backups:
   

2. •Any backup over 24 hours old, keeping only the first backup of each day.
   

3. •Any of those "daily" backups over 30 days old, keeping only the first of the week.
   

4. (Unless it's out of room, Time Machine will only delete 5 expired backups at a time.)
   

5. •If there isn't enough room for the new backup, Time Machine will delete any expired backups first;  if that doesn't make enough space, it will then delete the oldest backup(s). 
   

These deletions can be fairly quick, or may take quite a while, depending on how many items are involved.   And, the slower the connection to them, the longer it will take -- so if you're backing-up wirelessly, it will take much longer than to an external drive connected by FireWire.

Each deletion is documented in the system.log.  You can see or monitor these via the Console application or via the widget in section #A1.  

If you see a message saying "Found partially deleted backup;  trying again to delete," the named backup may be damaged -- Time Machine probably tried to delete it earlier, but couldn't.  If you see the same one on repeated backups, try deleting it via the Finder.  If that doesn't work, try repairing your backups, per item #A5.

Unless it's out of space, you can cancel a backup in this phase without causing a problem -- Time Machine will "catch up" the necessary deletions on subsequent backups.  Cancelling one that's out of room won't cause a serious problem, but it does mean no backup can be made.

(On Snow Leopard or Leopard, when Time Machine is out of room for backups made over a network, this can be extremely slow.  Time Machine must "compact" the sparse bundle after each deletion.  It's even worse if a "deep traversal" is required, as that is also performed after each one.)

Verifying Backup

For backups made over a network, Time Machine periodically (usually once a month) checks the integrity of the backups.   You can also do this manually, by holding the Alt/Option key while clicking the Time Machine icon in your menubar and selecting the Verify Backups option.

This was introduced with Snow Leopard (10.6.4), and on it and Lion (10.7.x), is done before the actual backup begins;  effective with Mountain Lion (10.8.x), it's done afterwards.  The more backups there are, and the slower the connection, the longer this will take. 

If the progress stops for a very long time, there may be a problem with the backups.  Try connecting via Ethernet cable if at all possible.  If not, or if that doesn't help, try repairing them, per item #A5.

Note that you can cancel the verification, by cancelling the backup (either click the Time Machine icon in your menubar and select Stop Backing Up, or click the small "X" icon at the end of the progress bar on the Time Machine preferences panel).  If you do this on Snow Leopard or Lion while the verification is running, it will stop the verification but continue to do the backup normally.   If you do it on Mountain Lion, the backup is already complete.