How do I know the date of my last succeful iCloud backup ?

Hi there, magdi207!
Thanks for reaching out to the Apple Support Communities! That is a great question you have about finding out when the last backup to iCloud was and I’m happy to help! Check out this article to Locate backups of your iPhone, iPad, and iPod touch. Specifically:

Locate and manage iOS backups stored in iCloud

If you use iCloud Backup, you won't find a list of your backups on iCloud.com. Here's how to find your iCloud backups on your iOS device, Mac, or PC.

On your iPhone, iPad, or iPod touch:

• Using iOS 11, go to Settings > [your name] > iCloud > Manage Storage > Backup.
• Using iOS 10.3, go to Settings > [your name] > iCloud. Tap the graph that shows your iCloud usage, then tap Manage Storage.
• Using iOS 10.2 or earlier, go to Settings > iCloud > Storage > Manage Storage.

Tap a backup to see more details about it, choose which information to back up, or delete the backup.

You can choose which content to back up only from the Settings menu of the device that stores that content. For example, while you can view your iPad backup from your iPhone, you can choose which iPad content to back up only from the Settings menu of your iPad.

On your Mac:

1. Choose Apple () menu > System Preferences.
2. Click iCloud.
3. Click Manage.
4. Select Backups.

On your PC:

1. Open iCloud for Windows
2. Click Storage.
3. Select Backup.

Learn more about how to delete or manage iCloud backups from your Mac or PC.

Take care!