how do i transfer data from my old imac to a new imac

Create a Time Machine backup or bootable clone of it, and then migrate your data from the backup drive while setting up the new iMac. If desired, you can instead migrate the data directly or drag-copy part or all of your home folder to over.

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I believe you will find a tutorial at Pondini's Time Machine FAQ. Also, see Move your content to a new Mac - Apple Support, but this requires an ability to use Target Disk Mode on both computers.

Clone using Restore Option of Disk Utility

1. Open Disk Utility in the Utilities folder.

2. Select the destination volume from the left side list.

3. Click on the Restore tab in the Disk Utility main window.

4. Select the destination volume from the left side list and drag

it to the Destination entry field.

5. Select the source volume from the left side list and drag it to

the Source entry field.

6. Double-check you got it right, then click on the Restore button.

Destination means an external backup drive. Source means the internal startup drive.

For Lion or later:

Clone Yosemite, Mavericks, Lion/Mountain Lion using Restore Option of Disk Utility

Restart the computer and after the chime press and hold down the Command and R keys until the Utility Menu appears.

1. Select Disk Utility from the Utility Menu then click on the Continue

button.

2. Select the destination volume from the left side list.

3. Click on the Restore tab in the Disk Utility main window.

4. Select the destination volume from the left side list and drag it

to the Destination entry field.

5. Select the source volume from the left side list and drag it to

the Source entry field.

6. Double-check you got it right, then click on the Restore button.

Destination means an external backup drive. Source means the internal startup drive.

[Exclusive permission to use the above has been granted to theratter by Kappy.]

You can find detailed guide at the following support page Move your content to a new Mac - Apple Support