Current Balance — The total amount of money owed on a credit card during the current billing period. (debt.org)
When upgrading your account you will receive an upgrade invoice for the additional amount owing until the end of your current billing period, then you will be invoiced at the new rate for your next billing period. (help.sharesight.com)
After I made my $ 600 purchase, I could have made a good guess — or called Citi and asked — when the current Billing Period ends. (mymoneycounselor.com)