What I would suggest you do is read both IB and the Exchange requirements (trading the contract on) for Margin so you know exactly what you are responsible for when using your trading account.
You are talking about the notional value of the contract. In futures, there are no finance fees for the amount of leverage you are using. Although if you go on a margin call, your positions can be liquidated.
you already 'pay' interest when you buy a futures contract, the payment is made through a premium you pay over the current price of the security on the spot market, the size of the premium is defined by how many months in the future the contract is, the libor, dividends etc. when you are short you 'get' the interest
you are not charged interest. although as dividends come off the cash S&P, the futures price is reduced by that much.
As I understand your question and the issue the 'margin' your referring to is the security or guarantee that you provide the broker in case your wrong. so instead of 'paying' interest you should be getting interest. Remember that a futures contract is only a contract to buy/sell something in the future and no money changes hands at the execution of the contract. it is only when the contract expires at the preset date that money changes hands (the amount of deposit is adjusted to/from your account daily to reflect price changes ) futures contracts themselves have an 'interest rate' built in. the reason is simple. "why buy something today and store it when you dont need it until X days from now and you could keep the money in the bank" so if the SP is 100 then a SP contract that is two months out may be 100.88 to reflect the value of the money from now till the end of the contract. In this way you can actually 'earn' a synthetic interest by buying the actual underlying and sell the future. like with EFPs on IB (something I do) in the end the 'margin' that the brokers are 'charging' (requiring would be more accurate a term) you is so that if the trade goes bad for you they dont have to chase you down for the money. While others that posted maybe could be a lot more polite they are 100% IMHO in the fact that you should do some more reading before placing trades so that you fully understand what your doing. This is not a job that you want to learn while you money is at stake. Also try to ignore those that would belittle you for trying to learn more, everyone has to learn sometime and the price is right for learning it here. Best of trading to you Bob
I would recomend you purchase a used copy of this book to learn a little about the futures market. You have to start some where and this is a good place. http://www.amazon.com/Options-Futur...=sr_1_1?ie=UTF8&s=books&qid=1195840295&sr=1-1
To further confuse: be aware of contango and backwardation! J/k, the only thing I can offer is that you do not pay interest on the 115k in your example. I won't tell you to go read a book because I assume you came on here for the quick and dirty answer.
Yes, thank you, I understand now....and I'm not gonna read a book about futures and stop sending me links to pdf files...
I'm really curious to see how many days it's going to take you to lose all your money with that attitude ... oh, and don't count on many members of ET to help you out with your next question, arrogant SOB ...