Unexpected use of mobile data for software updates

If you’re disconnected from Wi-Fi or it’s too slow, iOS will put up a prompt seeking permission to use cellular data. It should not do it without permission.

You should turn off Automatic Download as a basic prevention measure , in Settings, General, Software updates.

Remember this is a total since you last reset statistics. Does it show on your mobile account monthly bill?

iOS 18.6.2 is 5+ months out of date. Update to iOS 18.7.2 if you want to stay on iOS 18,, or update to iOS 26.1 if you want to install the latest iOS version.

I suspect it has downloaded 26.1 using mobile data!

If 26.1 has been downloaded, then you will see it if you Tap Settings > General > Storage and scroll down to look for iOS 26.1. If you don't see the file there, it has not been downloaded.

Unfortunately, there is no way to know whether a download occurred using Wi-Fi or Cellular Data. If Wi-Fi is enabled, the iPhone will always use Wi-Fi as a priority. Data would only be used if Wi-Fi was not available at the time and you have also enabled downloads of updates using cellular data.

grahamchiswick wrote:

Thanks LD150. So something else was downloaded using my mobile data allowance. Maybe iOS 18.7.2. ?

I believe all settings were set correctly to prevent use of mobile data for downloading software (iOS upgrades and app upgrades).

Since no one else has chipped in to say they have the same problem, I will just disable Automatic Updates on the Settings > General > Software Update screen.

Turn off Automatic Downloads as well, to avoid data usage, but as i say it should ask you to use cellular data, unless ,maybe you have the setting to allow more data on 5G turned on (I cant remember the exact wording)

I just wonder whether iOS updates use this particular setting, or is controlled separately

By default, updates will occur only when a good Wi-Fi connection is present.

IF......Wi-Fi is not available......AND.....you have authorized updates to be downloaded using cellular data, that would be the only way that a download over cellular would occur.

Based on the information that you have provided, I do not think that an update was downloaded over cellular data.

BTW ios26 would be 12-14 GB