BitFolk

This is what cacti is for:

https://tools.bitfolk.com/cacti/

Cacti doesn't show that though (without taking the average throughput and multiplying by the time range of the graph)?

What I mean is accumulated transfer for some period (months, probably) - basically, an archive of the "data transfer report" emails, with the data thrown at some graph library.

Yes, you have to multiply the average by the graph range in Cacti, but it's already an extremely capable graphing application. The alternative is writing our own one which would duplicate this and not be as good, just for the sake of it saying "XX GB in this graph" instead of "123kbit/sec average".

Another downside of Cacti however is that it reports all bandwidth usage whereas data transfer is only billed if it's destined for outside bitfolk's network.

Even if it's just a quick reference of "this is how much you used last month" to see if the current month is on track or not.

Total amounts transferred were added to Cacti so that no multiplication of data rates is required.

If you look at https://tools.bitfolk.com/cacti/graph.php?action=view&rra_id=all&local_graph_id=2673 you'll see that you transferred 70 / 64 GB in the last month. You can click the magnifying glass at top right to specify any time period you like.

Ahh, very useful, thanks.