Unfortunately, there's no way to get the number of email remaining on your plan with the SendGrid API at present (as a standard SendGrid User). You can, however, use the General Statistics endpoint and it's parameter requests
. You may then subtract requests
from the number of emails you have in your plan.
Doing so would look something like:
total_credits = 100000
statistics = SendgridToolkit::Statistics.new(api_user, api_key)
stats = statistics.retrieve_aggregate(:start_date => Date.today.beginning_of_month, :end_date => Date.today.end_of_month)
credits_left = total_credits - stats[:requests]
p credits_left
As an additional note, I wouldn't worry too much about going over your credit limit as at present overages are billed at 1¢ per 1,000 emails.