Looking at data usage break down per app, mine goes back to 2015 rather than for the current and last billing periods. Can I see the usage per app per billing period ?
iPhone 6 Plus
The iPhone doesn't break that down at all by billing period. You have to reset the statistics manually.
Add a dated repeating Reminder to reset usage statistics (Settings/Cellular, scroll to the bottom) at the start of your billing cycle.
There's also a 3rd party app (Dataman) that will track your usage (including Wi-Fi) that you can specify your billing period, and it will reset itself automatically.
But the best way to check is your carrier's website, or check if your carrier has an app that offers this feature. AT&T does, for example. And it has the advantage that if you have a shared data plan with other devices it will show the total, not just one device.
Detailed data usage for billing periods
