Data - what uses Data?

What kind of phone are we talking about? iPhone for example lets you examine what is using how much data...

When your phone can not use Wifi, it uses your cellular data instead... unless you have it switched into airplane mode.

This would include your emails... messages... updates... etc.

Thank you for responding.  It's an iPhone and when home or anywhere possible I use wifi to reduce data usage.  I have the ATT Go-Phone plan.

@Kitten54

I hope they explained what wifi assist is and does.  It is an Apple feature that allows your phone to choose the best network connection for fast, seamless operation.  It is supposed to augment wifi, not replace it.  In some cases the wifi is just not as good as the cellular connection so a phone chooses cellular over wifi despite being connected to your home wifi.

If turning off wifi assist helps control data use, you may also notice slower phone performance, buffering, etc.  You might what to trouble shoot your home network.  

Happy to help.  Data use is a topic I've spent some time on.  Trial and error, data overages and plenty of problems with it myself in the past. 

Your iPhone keeps a record of data used.  Open settings, cellular usage and scroll down.  Each app has the amount of data used since the last reset.

Another little iPhone specific thing is you have to reset the data stats every billing period.  My android phone resets itself.  

Kb is the smallest unit, then MBs then GBs.  

Note the picture on the left shows stocks, tips and watch apps turned off.  This prevents those apps from using cellular data.  You can turn off iCloud and iTunes to prevent updates or backup over cellular.  

I left wifi assist on in the photo, but you should turn it off.

imessage also uses data, rather than the free unlimited SMS messages 

In some bizarre cases, a phone malfunctions and uses data beyond normal.  A full factory reset can fix it, but in some cases a phone has to be replaced under warranty.

Thank you! 

I just got this new iphone and I was told my data plan was good to keep as I barely used 1/4 of it. Now, however,  I am getting charged $20.00 for overusage, when I have never used more than my plan in over 3 years! I went to 2 ATT stores and called in and no one could tell me what was causing me to increase my data usage.... Crazy!  I was so frustrated. One person did tell me if I turned off "location services", it would help... but it did not as I just got notified again that I was getting close to going over. 

I turned off a lot, based on your picture above and reset my usage count. I had no idea I needed to do this. It said the last time it was reset was in February, and I bought this phone in March..

Thank you for your post. I will watch now and see how things go.

I don't know how often WiFi assist kicks in, and I'm certain it varies per person, but since the last time I reset my iPhone counter:
I've used 24GB of cellular data.
19.6MB was WiFi assist. That is a pretty small percentage.

For comparison, during the same time period:
139 MB was Calandar.
12.2 MB was Contacts.
57.4 MB was Notes.

@lizdance40 Are we certain this is something that is still happening in current versions of iOS or it's something that happened when it first came out (maybe even in beta) and we're still talking about it??  I see you have it turned on and your usage appears to be nothing and the data goes back to October (I suppose that could be an old screen shot).

@anniec

glad it helped.   I learned about data usage the hard way, I have teenagers.   If you need help once you have some numbers, please send me a private message, so I don't miss your questions.