Does a Mac have a built-in duplicate file finder?

Not for all files. Photos has a Duplicates album, Music has File > Library > Show Duplicate Items, and for other files you can compare checksums with shasum in Terminal.

Why didn’t deleting duplicate files free up space on my Mac?

The copies were probably APFS clones, which share the same data blocks, so removing one frees almost nothing until every copy is gone. Files still in the Trash or held by Time Machine local snapshots also keep their space.

What is an APFS clone?

A clone is a copy of a file that points at the same data on disk instead of duplicating it, so it takes almost no extra space. If you edit one, only the changed parts are stored separately.

Does duplicating a file in Finder use more storage?

Not at first. On an APFS disk, File > Duplicate makes a clone that shares storage with the original. It only uses more space as you change one of the copies.

How can I tell if two files are clones?

macOS shows no clone marker, and Finder lists the full size for each copy. A copy made with Finder or cp -c on the same disk is almost always a clone, and deleting it barely changes your free space.

Is it safe to delete duplicate files on a Mac?

It is safe for your own documents, downloads and media once you have checked the contents match. Leave duplicates inside apps, ~/Library and photo or music libraries alone, and move files to the Trash rather than deleting them outright.

How to find duplicate files on a Mac (and why some aren’t taking space)

Use the Duplicates album in Photos for photos, Show Duplicate Items in Music for songs, and a short Terminal command that compares file contents for everything else. Before you delete anything, check how each copy was made. On APFS, a copy made with Finder's Duplicate or cp -c is a clone that shares its storage with the original, so deleting it frees little or nothing until every copy is gone.

What counts as a duplicate

A real duplicate is a file with exactly the same contents as another one. The name doesn't matter. IMG_2041.jpg and IMG_2041 copy.jpg may be identical, and two files both called report.pdf may be different. The only reliable test is comparing the contents, either byte by byte or with a checksum.

Common sources of real duplicates are the same download saved twice, photos imported from a phone more than once, old backups copied back onto the Mac, and project folders copied from an external drive.

APFS clones: duplicates that take no extra space

Every Mac running macOS High Sierra or later uses APFS on its internal disk. APFS can make a clone: a new file that points at the same data blocks as the original instead of copying them. Apple describes a clone as a copy that occupies no additional space. If you later edit one of the files, only the changed parts are written as new blocks. Everything else stays shared.

You often make clones without knowing it. These all create them when the copy stays on the same APFS volume:

File > Duplicate in Finder (Command-D).
Copy and paste, or Option-drag, within the same disk in Finder.
cp -c in Terminal, which asks for a clone.
Many apps that copy files with Apple's own file APIs.

Files downloaded twice, copied from another drive, received over AirDrop or restored from a backup are separate copies. Those really do use space twice.

Why this matters when you delete

Say you have a 4 GB video and a Finder duplicate of it. Get Info shows 4 GB for each, so it looks like 8 GB. On disk it is about 4 GB in total. Delete the duplicate and you get back almost nothing. The blocks stay in use by the original. They are only freed when every copy that shares them is gone.

That is why a duplicate finder that ignores clones can promise space you never receive. It counts each extra copy at full size, you delete them, and free space barely moves.

How to tell if a copy is a clone

macOS doesn't mark clones anywhere you can see. Finder, Get Info, ls and du all show the full size for each copy. You can still work it out:

Think about how the copy was made. A file you duplicated in Finder on the same disk is almost certainly a clone. A second download is not.
Watch free space. Note the available space, move one copy to the Trash, empty the Trash, then check again. If it barely changed, the copy was a clone, or something else is holding the blocks (see the next point).
Remember snapshots. Time Machine local snapshots can keep deleted files on disk for a while, which makes any file look like it freed nothing. See how to delete Time Machine local snapshots.

You can see clones in action safely. This makes a clone of a file, then shows free space. Run df -h / before and after and the available space hardly changes. Replace the file name with a large file of your own, and delete the copy afterwards.

cp -c ~/Movies/big.mov ~/Movies/big-clone.mov && df -h /

Find duplicates with built-in tools

Photos

In the Photos app on macOS Ventura or later, look for Duplicates under Utilities in the sidebar. Photos groups exact copies and near copies, such as the same picture at different resolutions. Click Merge to keep the best version with its combined details. Merged extras go to Recently Deleted, where you can recover them for a limited time. If you use iCloud Photos, merging also applies on your other devices.

Music

In the Music app, choose File > Library > Show Duplicate Items. Hold the Option key and the menu changes to Show Exact Duplicate Items, which is stricter. Check each pair before deleting, because the same song on two albums is listed too.

Finder

Finder has no duplicate search, but you can narrow things down. In a folder such as Downloads, choose View > as List, then View > Show View Options and turn on Calculate all sizes. Sort by Size. Files with the same size and similar names sit next to each other, and you can compare them with Quick Look (Space).

Terminal: compare contents

This command checksums every file over 10 MB in your Downloads folder and prints the ones whose contents match, grouped together. It only reads files and deletes nothing. It can take a while, because it reads every file it checks in full.

find ~/Downloads -type f -size +10M -print0 | xargs -0 shasum -a 256 | sort |
  awk '{ if ($1 == prev) { if (!shown) print last; print; shown = 1 } else shown = 0; prev = $1; last = $0 }'

Each line starts with a checksum, followed by the path. Lines with the same checksum are identical files. Change ~/Downloads and +10M to search other folders or smaller files.

Avoid running it on iCloud Drive or other cloud folders. Reading a file that is stored only in the cloud makes macOS download it first, which can fill your disk while you are trying to clear it.

Delete duplicates safely

Decide which copy to keep. Keep the one in the folder where you expect to find it, usually not the one in Downloads.
Check whether it is a clone. If it was made with Finder's Duplicate on the same disk, deleting it won't free much. Only delete it to tidy up.
Move it to the Trash, not rm, so you can restore it with Put Back if something was linking to it.
Empty the Trash once you are sure. The space only returns then.

What not to delete

Files inside app bundles, ~/Library or system folders. Apps often ship identical files on purpose. Removing one can break the app.
Files inside a Photos or Music library package. Use the apps' own duplicate tools instead of Finder, or the library can lose track of them.
Project and dependency folders. Identical files across developer projects are normal. Removing whole node_modules folders is a better way to reclaim that space.
Your only backup. A copy on purpose in a backup folder is not clutter.

If you are hunting for space in general, duplicates are rarely the biggest win. Start with finding large files or the safe order for a full Mac.

A duplicate finder that knows about clones

freedisk.space finds duplicates as part of a normal scan. It compares local files in stages by size and then content, so files with the same name but different contents are never grouped. Cloud-only placeholders are skipped rather than downloaded. When copies are APFS clones of each other, it labels them as shared storage and explains that removing one frees nothing until every copy goes, so they don't inflate the space you could reclaim. When you choose copies to remove, they go to a Cleanup list. You confirm, they move to the Trash, and Put Back works if you change your mind. Scans run on your Mac and nothing is uploaded.

Questions people ask

Does a Mac have a built-in duplicate file finder?: Not for all files. Photos has a Duplicates album, Music has File > Library > Show Duplicate Items, and for other files you can compare checksums with shasum in Terminal.
Why didn’t deleting duplicate files free up space on my Mac?: The copies were probably APFS clones, which share the same data blocks, so removing one frees almost nothing until every copy is gone. Files still in the Trash or held by Time Machine local snapshots also keep their space.
What is an APFS clone?: A clone is a copy of a file that points at the same data on disk instead of duplicating it, so it takes almost no extra space. If you edit one, only the changed parts are stored separately.
Does duplicating a file in Finder use more storage?: Not at first. On an APFS disk, File > Duplicate makes a clone that shares storage with the original. It only uses more space as you change one of the copies.
How can I tell if two files are clones?: macOS shows no clone marker, and Finder lists the full size for each copy. A copy made with Finder or cp -c on the same disk is almost always a clone, and deleting it barely changes your free space.
Is it safe to delete duplicate files on a Mac?: It is safe for your own documents, downloads and media once you have checked the contents match. Leave duplicates inside apps, ~/Library and photo or music libraries alone, and move files to the Trash rather than deleting them outright.