How is bandwidth calculated


It's calculated monthly. Each plan includes a monthly bandwidth allotment.

When is there a notice emailed out?

I'm sorry I was mutlitasking when I posted the question and didn't finish. So if I have a the 400gb bandwidth plan, at what level will I get a notice that I am nearing the bandwidth limit for a particular month? 380? 399?
The setting is currently at 80%. So at 400 gigs bandwidth, you'd get a warning at 320 gigs used :)