Oilyboid,
The buying power/margin in IB margin account is dynamnicly calculated in realtime, hence you don't have to worry about exceeding your buying power - such an order will be rejected.
Currently, Daytrading buying power is NOT a fixed amout that reduces with each daytrade. Your current buying power fluctuates as you open and close positions.
The same buying power can be used multiple times during the same trading session. For example, an account with $10,000 can open and close any number of positions provided that each purchase is offset with a corresponding sale before a new purchase is initiated (sequential trading) or if
no single purchase exceeds the account's "buying" power ( two times the maintenance margin excess).
This will change with the implementation of the new daytrading margin rules, because they define and treat daytrading margin/buying power differently.
Fohat