When you purchase a plan with Project Fi, your new plan will automatically come with several amazing features, including rollover data. This mean that Project Fi will credit the money for data you don’t use to your next statement. If you use more than you planned, you’ll still pay the same $10/GB.
How it works:
Select how much data you need: Let's say you go with 5 GB.
At the end of the month: If you used only 3.0 GB, that's 2.0 GB unused and $20 back on your statement.
If you go over by, say, 0.40 GB, Project Fi will charge you $4.00 more on your next statement—no extra fees.