How much phone data do you need?
Read your past usage first, then pick a plan size.
Start with your own numbers
Your phone settings and your carrier account show how much data you used in past months. Note the highest month, not only the average.
If you are new to data
The FCC says: "If you're new to data and text, choose a plan that seems right and monitor your usage during the first few weeks to see if you are approaching your limit."
Heavy use
The FCC says: "If your data or text usage is high, consider an unlimited data plan option." Read what the carrier means by unlimited, including any slowdown after a set amount.
Overage and slowdowns
The FCC lists "Downloading fees" for downloading more data "than the plan allows." Check what happens at your limit: a charge, a slowdown, or a stop.
Wi-Fi at home and work
Data used on Wi-Fi usually does not count against your plan data. If you are on Wi-Fi most of the day, check your own usage before you pick a size.
Alerts
The FCC suggests asking your carrier how to avoid bill shock, such as phone or text alerts or monitoring your account online.
This is general information, not legal advice. Plan terms come from the carrier.
Sources: FCC, Understanding Your Telephone Bill.
FAQ
Next: plan checklist
A short list before you switch.
