When you check your iCloud storage and see a large number of messages backed up, it’s important to understand that this count refers to all data associated with the Messages app. That includes text messages, iMessages, photos, videos, stickers, reactions (like thumbs-ups or hearts), and even group messages. So, if you noticed an increase of 700 messages overnight, it doesn’t necessarily mean 700 new text conversations were sent or received. It could also reflect attachments being synced, reactions in group chats, or old data syncing in from other devices linked to your Apple ID.
Regarding your past situation where you merged Apple IDs and saw someone else’s calendar and contacts, it’s possible that their data—including messages—synced to your device at the time. However, once you signed out of that Apple ID and started using your own, syncing from their account should have stopped. That said, residual data from that time may still be lingering in your current iCloud account, especially if you restored a backup that included those old messages or if you didn’t manually clear them out.
Another possibility is that an old device, like a Mac or iPad, is still signed in with your current Apple ID and syncing older message data back to iCloud. This can cause the message count to rise unexpectedly, especially if those devices were offline for a while and then reconnected.
To investigate, start by checking which devices are currently signed into your Apple ID. Go to Settings > [Your Name] and scroll down to see all connected devices. If you notice a device you no longer use or recognize, tap on it and choose Remove from Account to disconnect it.
Next, review your iCloud Messages settings by going to Settings > [Your Name] > iCloud > Show All > Messages. Ensure Messages in iCloud is toggled on. If you’re using multiple Apple devices, such as an iPad or Mac, they may still be syncing older content to iCloud. It’s a good idea to check and clean up messages on those devices as well.
You can also go into the Messages app and look at individual conversations. Tap the contact’s name at the top of a conversation, then tap Info and scroll down to see attachments. You might find old photos or videos that are contributing to the increased storage. Deleting those attachments can help reduce the message count and free up space in iCloud.
If you suspect that old or merged data is the reason your message count is inflated and you're comfortable with starting fresh, you could consider resetting Messages in iCloud. You can do this by going to iCloud.com, accessing Account Settings, and using the Restore Messages or Clear Messages option under Advanced. Another way is to go to your iPhone’s iCloud settings, turn off Messages in iCloud, choose “Delete from iCloud,” and then re-enable it. Be cautious with this step—it will permanently delete all synced messages across your devices.
In summary, your situation is not unusual, and you're not imagining things. Messages in iCloud can increase in size for a variety of reasons, including old attachments, syncing across devices, or leftover data from a previous Apple ID.
