The monthly limit for external funds transfer is the maximum amount you can transfer in a rolling 30-day period. It includes all transfers processed during that time frame.
All external transfers made within the past 30 days are subtracted from the limit to determine the total amount of funds available to transfer.
Your transfer limit is found by going to the Move Money Tab, selecting To/From my Other Bank Account (external) option and by clicking on the information icon next to the Amount($) field.