Can I delete a DMG file after installing the app?

Yes. Once the app has been copied into your Applications folder and opens correctly, the DMG is no longer needed. The installed app is a complete, independent copy and does not read anything from the disk image.

Will deleting the DMG break the app?

No, as long as you copied the app to your Applications folder rather than launching it directly from the mounted disk image. If the app only ever ran from the image, delete nothing until you have copied it out.

Why does macOS say the disk is in use when I try to eject it?

Something is still reading from the mounted volume — usually the app running from the image itself, an open Finder window, or a Terminal session with that volume as its working directory. Quit the app, close the window, and eject again.

Should I keep DMG files as backups?

Generally no. Most developers keep old versions available for download, and a kept DMG goes stale as soon as the app updates itself. The exception is paid or discontinued software where the download may disappear, or a specific older version you rely on.

What to Do With a DMG File After Installing

Just delete it! Once the app is in your Applications folder and launches, the disk image has no further purpose. Keeping it doesn't make the app more stable, doesn't help it update, and doesn't protect you from anything. It just takes up space.

Why it's safe to delete

A DMG is a shipping container. Installing an app means copying it out of that container onto your real disk — the app in /Applications is a complete, self-contained copy that never looks back at the image it came from. Throwing away the container has no more effect on the app than recycling the cardboard box a monitor arrived in.

One thing to check: make sure you actually copied the app out. If you've been launching it straight from the mounted disk image in the Finder sidebar, you never installed anything. Drag it to Applications first — see how to install a Mac app from a DMG — then delete the image.

Eject first, then trash

Delete the file, not the mounted volume. In Finder you'll often see both: the .dmg file in Downloads, and a mounted volume under Locations in the sidebar.

Eject the mounted volume — click the eject arrow beside it in the sidebar, or select it and press Command-E.
Then drag the .dmg file itself to the Trash, or select it and press Command-Delete.

If macOS refuses to eject and says the disk is in use, something is still reading from it: the app running from the image, a Finder window open inside it, a Terminal session sitting in that directory, or occasionally Spotlight still indexing. Quit the app, close the windows, wait a moment, and try again.

The cases where you might keep one

Uncommon:

Discontinued or paid software. If the developer has gone quiet or the download sits behind a licence you'd have to re-purchase, an archived installer is genuinely useful. Move it out of Downloads into a folder you actually back up.
A specific old version you depend on. When a newer release breaks a workflow or drops a feature, the DMG for the version that works is worth keeping.
You're installing on several Macs offline. Keep it until you're done, then delete it.

For everything else, the developer's download page is a better archive than your Downloads folder. 99% of the time, keeping the .dmg just takes up space on your machine. And some of them can be pretty big!

Clearing out the ones you already have

Most Macs have years of these piled up. To find them, open Finder, press Command-F, set the search to This Mac, then set the filter to Name → ends with → .dmg. Add the Size column and sort by it — the worst offenders are usually a few large ones.

Alternatively, System Settings → General → Storage has a Documents section with a File Browser that surfaces large files by folder, and Downloads is nearly always near the top.

Empty the Trash afterwards to fully reclaim the space.

Or don't think about it at all

If you don't want to worry about this, EasyDMG has a setting to move the DMG to the Trash after a successful install. The disk image unmounts on its own, the installer goes to the Trash, and your Downloads folder stops collecting gigabytes of files you were only ever going to delete later.

It's opt-in, and it only fires when the install actually succeeded. If anything looked unusual and EasyDMG handed the image back to you to install manually, nothing gets thrown away.

Install, clean up, done. EasyDMG is free, open source, signed and notarized, and runs on macOS 13 or later.

Download EasyDMG