如何做空比特币

    以比特币单价1,100美元的执行价格出售十分之一个比特币的看跌合约，每一份合约的成本为0.045个比特币或49.50美元。合约于月底期满，如果期满时比特币的价格超过1,100美元，则各个合约便毫无价值可言。但如果比特币价格下跌，则合约价值将上涨。

    假设截止12月底，比特币价格已经下跌到500美元，即在不到一个月时间内暴跌55%。

    此时，比特币看跌合约的价格将上涨。

    可问题在于：要实现利润，我最终希望拿到的是美元。

    在正常的货币期权交易时，投资者可以将做空其他货币所使用的货币作为结算货币。所以，如果用美元来做空欧元，则在合约结算时可以使用美元，进而抵消欧元价值下跌这一事实。

    但目前在比特币期权中却无法如此操作。所有比特币期权和期货合约均以比特币进行结算。这是非常不划算的交易。原因在于，即使投资者最终从比特币期权中获益，最终兑换成美元的价值仍要大打折扣。

    以下是计算过程：

    开立账户必须提供0.1个比特币，按周四上午的价格约合110美元。

    看跌期权的成本为0.045个比特币，账户中剩余0.055个比特币。

    按照我们上面的假设，比特币价格暴跌55%之后，看跌合约的价值将上涨到0.12个比特币。加上账户中剩余的金额，目前共有0.175个比特币。

    而按500美元的单价将比特币兑换成美元，仅有87.50美元。

    这意味着，即便投资者的决策正确，预测了比特币泡沫的极限，也准确估算出比特币价格暴跌跌55%的事实，可最终依然要损失22.50美元。

    投资者也可以通过加大做空投入来减少损失。如果投资者以99美元买入两笔合约，而比特币价格还是下跌60%，最终投资者可以获利15美元。这其中尚未考虑手续费，整笔交易的手续费约为4美元，包括美元与比特币的兑换费用，此时利润将降至11美元。

    此外，比特币期权交易并不像在纽交所（New York Stock Exchange）进行的交易那样。周三中午，MPEx关闭交易，合约的价格不知所踪。据称这种情况经常发生。截止周四早些时候，该交易所仍未公布价格。而且，我与Coinbr的经纪人在会议室计算了相关交易数据，最终我得出的结论是，这种交易毫无意义，于是他主动提出将合约按0.033个比特币的价格出售给我，这样一来，0.1个比特币便可以购买三份合约，而不是两份。这让我不由得质疑，MPEx所报的价格到底有几分可信。

    这或许也解释了为何近期比特币的价格会一路暴涨。既然如此，为什么还要费心去做空它呢？（财富中文网）

    译者：刘进龙/汪浩   

    It cost 0.045 of a bitcoin, or $49.50, to buy a put contract to sell 1/10 of a bitcoin at a strike price of $1,100 per bitcoin. The contract expires at the end of the month and will expire worthless if the price of a bitcoin is above $1100 at that point. But the value of the contract will go up before then as long as the value of a bitcoin drops.

    Let's supposed bitcoins were to fall to $500 by the end of December, a 55% plunge in less than a month.

    If that were to happen, the price of my bitcoin put contract would jump.

    Here's the problem: To book my profit, I ultimately want dollars.

    With normal currency options you can choose to collect in whatever currency you are using to bet against another currency. So if you are betting the price of a euro will fall against a dollar, you can collect in dollars when the contract settles, thereby offsetting the fact that the euro just dropped in value.

    You can't currently do that with bitcoins. All of the bitcoin options and futures contracts are settled in bitcoins. This is a very bad deal. Because even if I end up with a bitcoin windfall, they will be worth a lot less when I convert them back into dollars.

    Here's the math:

    To open an account, it has to be funded with 0.1 bitcoin, which will cost $110 as of Thursday morning.

    The put option costs 0.045 bitcoins, leaving 0.055 bitcoins still in the account.

    After our imagined 55% plunge, the value of the put contract has soared to 0.12 bitcoins.

    Combine that with what is still in the account, and it's now 0.175 bitcoins.

    At a bitcoin price of $500, that's a mere $87.50.

    That means even if you are right, and you call the top of the bitcoin bubble, correctly predicting a whopping 55% plunge in the value of the currency and do all of this, you would lose $22.50.

    You can get around this by upping your bet against bitcoins. If instead you buy two contracts, for $99, and once again the price plunges 60%, you will end up making a whopping $15. And I haven't factored in fees, which would probably run you about $4 for the whole transaction, including the dollar-to-bitcoin round trip, taking your profit down to $11.

    On top of all that, this isn't like trading on the New York Stock Exchange. Midday Wednesday, MPEx appeared to shut down, and the prices of the contracts disappeared. I was told this happens a lot. As of early Thursday, the exchange still wasn't listing prices. What's more, after running through my math of the trade with a Coinbr broker in a chat room, with the conclusion that there basically the trade doesn't make sense, he offered to sell me contracts at 0.033 bitcoins, so I could buy three contracts instead of two with my 0.1 bitcoins. That led me to question just how real the prices MPEx was quoting were.

    All of this may explain one reason why the price of bitcoins until recently has been heading straight up. Why bother betting against it?