How do I stop my partner's data from backing up to my iCloud account?

Needing-answers wrote: …Hi my partner has a different iCloud account from mine. Said he never created it, but his data and my data are backing up to the same iCloud.

How do I stop this?

Change your password, and keep it private.

Several "if"s here... If your partner does indeed have their own account and you are using Family Sharing with you as the Organizer then you might have joint iCloud storage. Even then their content would not be mixed with yours but would be kept isolated in its own area. Think of a room with a movable wall with each of your content in its own area to which each of you have sole access.

Alternatively, if you are sharing an account (not a good idea) then you could end up with your content mixed together in a single storage area with the other having full access to that area.

Read this support article about Apple Account Frequently Asked Questions --> https://account.apple.com/faq

"How many Apple Accounts do I need?

Just one. Use the same Apple Account everywhere you sign in to ensure that all your Apple services and devices work together seamlessly and you can access your personal information from all your devices.."

Make sure that each family member has a unique Apple ID --> Make sure that each family member has their own Apple Account - Apple Support

- "If you want to share purchases or subscriptions with family, use Family Sharing. Each person should use their own Apple Account.”

You need to determine if you are indeed sharing a single account (do you share the same email address and password?), and if you are then one of you will need to set up their own account. While setting up the account may be easy, transferring the content may be complicated. Post again if you think you need to do that and we can help you with that.