You are connected to your home Wi-Fi, yet the mobile-data counter has increased. That deserves a closer look, but it does not identify the cause by itself. Start with the phone’s assistance setting and the time period covered by the counter.
Apple’s iOS 27 documentation calls the feature Connectivity Assist. It can use cellular data alongside a weak or unusable Wi-Fi connection. It replaces the older Wi-Fi Assist setting, and the menu location has changed.
Find the setting for your version
In iOS 27, look in Settings, Wi-Fi for Connectivity Assist. On older software, the name may be Wi-Fi Assist under Cellular. Check the iOS version before concluding that the option is missing; the displayed wording also depends on the phone’s language.
The current guide describes a separate cellular-usage count for Connectivity Assist. Record it before experimenting. Do not reset it just to make the screen look tidy: that removes useful context from your comparison.
Compare a small, ordinary task
Note the time, selected Wi-Fi network, assistance setting and counter. Try a brief task you would normally perform, such as opening a text page, then compare the figures. Avoid using a large download as the test.
An increase in overall cellular usage alone does not establish that assistance caused it. Compare the feature’s counter, the wider cellular statistics and your operator’s usage period. Those periods may not line up.
If your priority is controlling mobile-data use, review whether assistance should remain enabled. Turning it off is not a repair for the underlying Wi-Fi problem. Record your decision and, if the connection still feels unreliable, investigate the Wi-Fi connection separately.