"I want to guestimate a potential worst case max loss on a position. " More than you can ever imagine. The past is little help in deciding the worst case. You have to imagine a horrific international event, that blows out everyone's expectations, and stop losses, limitups, whatever are no use in a market where no one wants the other side of your trade. You can lose everything in your account. If you are leveraged, you can lose a lot more, and even bankruptcy may not protect you against thebroker coming after your money (and no broker is going to let you surround yourself with an LLC so they are stuck with a loss). Yes, you could buy options instead of getting into instrumcents to limit losses, but then of course, you pay a constant time value loss of the option.