Encryption we use does incur an additional overhead but it's relatively small. There are however two typical situations that you should take into account:

  1. active use - here the data overhead is usually between 0.5% - 1% as it depends on the device you use and the network provider (e.g., your mobile phone operator or broadband / fibre provider). 
  2. notifications / background app refresh - we are not sure what exactly the overhead here is but one notification seems to be about 6kB of data with usual (i.e., short) payload. 

It means that for each giga byte of data (1 GB), using Secure Spaces will add about 5-10 MB to your data usage. If you do worry about your data usage, we recommend switching off automatic background app refresh on your mobile devices.

All of us, though, are curious about how much data we are using. Private Spaces provide a simple statistics for you - simply go to http://private.space and you can check your usage today, over the last week, and month.