All residential data is billed PER GIGABYTE. There is no bandwidth restriction, other than your balance. A common question is “how much do I need for X use”. This varies very heavily on your use, your software, and the site. Some sites will have a higher data usage, where as others will use very little. In this case, it is recommended you top up with a little extra to account for any extra data usage.
If you need to check your balance, you can do this on the dashboard. Below you will see a list of pricings and expiries: