If an old Time Machine backup is filling an external drive, first check whether Time Machine is still using it and whether you need anything in that backup. For an active backup disk, let Time Machine manage its history, exclude only files you can replace or back up elsewhere, or move to a larger disk. If the drive belongs to an old Mac or you want to erase it, preserve anything you may need before making changes: deleting or erasing backups can remove your only copy of past files.

Check what the drive is used for

Connect the drive and open Apple menu > System Settings > General > Time Machine. Check whether it appears as a current backup disk. If it does, macOS normally deletes older backups as the disk fills so it can make newer ones. A drive showing little free space is not, by itself, a reason to manually remove backup files. Apple explains how Time Machine manages a full backup disk.

If the backup is from a previous Mac, or the disk is no longer selected in Time Machine settings, decide whether you still need to retrieve files from it. Open Time Machine and browse the available backups if you are looking for a particular document or older version. Restore anything you want to keep to your Mac or another storage location, and open it to confirm it is usable before deleting the backup. Time Machine supports restoring files from a backup; the backup disk is valuable precisely because it can preserve earlier versions. Apple’s Time Machine guide describes local snapshots and recovery.

Free space on a backup disk you still use

Exclude large items you can replace

If the drive is still active, use Time Machine settings to stop backing up bulky items that do not need historical versions, such as a cache or a large working folder already backed up elsewhere. On current macOS versions, go to System Settings > General > Time Machine > Options, click Add, choose the item, then click Done or Save if shown. Apple documents exclusions as a way to save space on the backup disk. See Apple’s steps for excluding items.

Choose carefully: an excluded item will not be included in future backups, and Apple notes that excluded items can still appear in local snapshots on the Mac. Excluding a folder does not retroactively clean up the old backup history already on the external disk. Keep an independent copy of important files before removing them from backup coverage.

Give Time Machine more room

If you want to retain broad backup coverage and the disk repeatedly runs out of capacity, use a larger drive. Apple recommends a backup device with at least twice the storage capacity of the Mac as a general target. To add a replacement, connect it, open System Settings > General > Time Machine, select Add Backup Disk, and follow the setup prompts. The Mac may ask to erase the selected device, so verify that you have the right disk and that it contains nothing you need before agreeing. Apple’s setup guide covers capacity and adding a backup disk.

If you want to reuse or erase the old drive

After recovering anything you need, you can erase the drive in Disk Utility and set it up again, or use it for another purpose. Erasing removes the backup history and other data on the selected disk or volume; check the name and capacity in Disk Utility before confirming. If Time Machine offers to erase a disk while setting it up, treat that as a destructive action too. Apple documents reformatting as permanently deleting backups and other data on the disk. Apple’s backup guide explains the erase prompt.

Avoid deleting files by hand inside a Time Machine backup folder in Finder. Apple’s supported guidance is to let Time Machine remove older backups automatically, exclude chosen items from future backups, or select a different disk; it does not provide a normal Finder workflow for manually pruning old backup dates. If you need a particular old version, retrieve it before changing the disk.

Decide which option fits

Keep the existing disk unchanged if you still need its older versions and it continues to back up. Exclude specific replaceable data if you can accept that it will no longer be covered by future backups. Choose a larger disk if you want to preserve a broad history. Erase the old disk only after confirming you have recovered or independently saved anything important. When the new disk is ready, run a backup and check Time Machine’s status to confirm it completes. The safest space-saving choice is the smallest change that preserves the files and history you still rely on.

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