Unless you’re on an unlimited data plan, there’s always the possibility you’ll hit or go over your 3G or 4G allowance for the month. Here are some easy ways to cut down on the amount of data your iPhone uses. See: iOS 8 vs iOS 9
Update 28 September: Since iOS 9 was introduced some users will find themselves using more cellular data. This is likely due to a new Wi-Fi Assist feature, which automatically switches to cellular data when the Wi-Fi signal is poor. If you have a limited data plan, it's a good idea to check whether this is enabled. Go to Settings, Cellular and ensure Wi-Fi Assist is disabled.
Some smartphones are more efficient than others when it comes to mobile data. Apple provides plenty of settings to restrict mobile data on your iPhone, but doesn’t make it easy to see how much of your allowance you’ve used.
If you go to Settings, Mobile, then scroll down to Mobile Data Usage, you’ll see two counters: Current Period and Current Period Roaming. This shows the amount of kilobytes or megabytes used since you last reset the statistics (an option at the bottom of this particular menu).
And here’s the rub: it’s up to you to reset the counters at the moment your contract (or pay as you go package) begins a new month. Otherwise the figures shown are totally unhelpful.
However, you may be in luck as several mobile operators offer their own apps which keep a track of your usage, so you might not need to use Apple’s counters. Bear in mind that even if there is an app, the figures may not be up to date, so be careful if you’re near the limit and will be billed if you go over it.
How to cut down on mobile data: change your settings
Below the Mobile Data Usage counters in Settings > Mobile is a list of apps which can use mobile data. By default, they will all be enabled, so you can stop certain apps eating through your allowance by toggling them off here.
They will be able to use Wi-Fi, when available, but when out of range, they may not be usable, depending on whether they need to connect to the internet to work.
How to cut down on mobile data: change settings within apps
Some apps have their own settings which restrict particular functions to Wi-Fi only. An example is Dropbox, which can be a big data hog if you use it to back up the photos and videos from your iPhone’s camera roll.
There’s a settings tab in the Dropbox app which lets you disable mobile data, preventing the app from uploading videos when there’s no Wi-Fi connection.
Check your other apps for similar settings.
How to cut down on mobile data: disable background app refresh
Introduced in iOS 7, Background App Refresh is a great feature if you like your apps to show the latest information when you launch them, instead of only then downloading the latest news, weather or other information.
However, this can needlessly burn through mobile data if you don’t regularly open those apps.
It’s easy to stop this happening by launching Settings, then tapping General, and scrolling down to Background App Refresh. Here you can disable the feature altogether, or prevent specific apps from updating in the background.
How to cut down on mobile data: turn off mobile data
It might sound obvious, but the easiest way to cut down on mobile data use is to enable it only when you need it. That requires a trip into the Settings app, since there’s no toggle for mobile data in the new iOS 7 Control Centre. But it could be worth the hassle if you’re getting near your data cap.