IBackup Professional retains upto 30 versions of a single file. It calculates the total storage space for only the latest version, and not the previous copies. For a typical account, this means that you get nearly an overall storage capacity that may be twice or higher the storage capacity you opt for.

If your usage exceeds the opted storage plan, there is no need to necessarily upgrade to the next higher plan. You will be charged at USD 2 per GB per month, for over usage.