SD card is read-only? What to check

Your SD card opens, and you can see your files, but you cannot save, delete or change anything. A lock switch or card reader may be the cause, but a damaged file system or a card that is failing can also turn read-only.

Start by protecting the files already on the card. Then check whether the problem follows the card or stays with one device. The USB & SD Speed Test can help compare read and write performance after the card is writable again.

Check the card safely

1. Protect your files first. Copy any readable files to your computer or another safe location. The USB & SD Speed Test measures read and write speed, so do not run its write test until you have a backup and the card accepts writes.
2. Check the lock switch. If you use a full-size SD card or a microSD-to-SD adapter, look for the small sliding switch on its side. Move it toward the unlocked position, usually toward the card's contacts. Do not force it. MicroSD cards themselves generally do not have this switch.
3. Try a small test file. In File Explorer or Finder, create a new empty file on the card, then delete that file. If you get a read-only or write-protection message, note the exact wording. Do not try this if the only copy of important files is on the card.
4. Compare another reader or device. Use a different card reader or adapter, and try the card in another computer if possible. If it works elsewhere, the first reader, adapter or device settings are more likely to be the cause.
5. Measure speed after writes work. Once the card is backed up and can save a test file, open the USB & SD Speed Test, select the card if prompted, and run the test. Use the result to check whether read or write performance is unusually low or inconsistent.

What the result means

The card works after moving the lock switch

The switch was probably in the locked position, or the reader was detecting it that way. Some card readers are sensitive to a loose or damaged switch on the adapter. If moving the switch does not help, try another adapter rather than pushing the switch harder.

The card is writable in another reader

The card itself may be fine. The original reader, USB port or adapter may be faulty, or the first device may be mounting it as read-only. Keep using the working reader for now and check the device that failed.

Only one app cannot save to the card

The card may be writable, while that app lacks permission to use the card or the folder you chose. Try saving a new file to another folder on the card using the device's file manager. If that works, check the app's storage or file access permissions instead of changing the card.

Every device reports the card as read-only

If the switch and reader are not the cause, the file system may have errors, or the card may be protecting its data because it is failing. Copy what you can before attempting repairs. Do not format it just to clear the warning: formatting erases the card and may not fix a failing card.

The card saves files, but speed is poor or inconsistent

A card can accept writes and still be slow, worn or unreliable. Compare results using the same reader and port. A speed test is not a complete health check, and it cannot prove that every file will remain safe.

How to fix it

1. Unlock the card or replace the adapter. Slide the lock tab on a full-size SD card or adapter toward the unlocked position. If the tab is loose, missing or does not stay put, try a different adapter.
2. Reconnect the reader. Remove and reinsert the card, then try another USB port or reader. Avoid repeatedly disconnecting it while files are being copied.
3. Check whether the issue is app-specific. On Android, try creating or moving a file with the phone's file manager. If only one app is blocked, check Settings › Apps › [app] › Permissions; the exact permission names vary by Android version. On a computer, test with a simple new file in the card's main folder.
4. Check file access settings. In Windows 11, open File Explorer › This PC, right-click the card, and choose Properties › Security, if that tab is available. On macOS, select the card in Finder and choose File › Get Info › Sharing & Permissions. Permission controls may not appear for every card format, and they will not fix a locked card or damaged file system.
5. Check the file system after backing up. On Windows 11, use File Explorer › This PC › right-click the card › Properties › Tools › Check. On macOS, open Applications › Utilities › Disk Utility, select the card, and choose First Aid. A repair can change data, so do this only after copying important files elsewhere.
6. Replace the card if it stays read-only. If it remains write-protected in more than one reader and on more than one device, stop relying on it. Copy the remaining files if possible, then replace the card rather than using it for new photos or documents.

When it's the card, not a setting

Some SD cards switch to permanent read-only mode when their internal controller detects a problem. This can protect existing data, but it usually means the card is near failure. A card that repeatedly disconnects, produces copy errors, or becomes read-only in multiple devices is not dependable storage. Save the files elsewhere and replace the card. Do not keep testing it with important data at risk.

Why a card can become read-only

Read-only is a state, not a diagnosis. A physical lock tab can tell a reader to block writes. An operating system can mount a card as read-only after detecting file system errors. An app may also lack access even when the card itself is writable. Testing with a second reader and a second device helps separate those cases.

Use the USB & SD Speed Test only after you have copied important files and confirmed that the card accepts writes. Its speed results can help compare performance, but they cannot establish that a failing card is safe for long-term storage.