It depends on the brokerage. There is Reg T. margin and then there is portfolio margin (the latter has significantly higher capital deposit requirements). It a

It depends on the brokerage. There is Reg T. margin and then there is portfolio margin (the latter has significantly higher capital deposit requirements). It also is not a straight 1:1 ratio. You generally can't go absolutely nuclear with leverage unless you have portfolio margin. Typically, brokerages will require collateral in the account equal to the risk (for defined risk strategies) and you will need a higher trading clearance on your account for unlimited risk. Your buying power is a function of how long the trade will be held as well as the risk profile.