Does an option trading below parity always indicate an arbitrage opportunity?
"Probably but not necessarily.  Your question could also be posed regarding cash & carry for commodities in contango: If I can take delivery on the gold now, short the gold next year and make delivery then, paying the storage fees, is this an arbitrage opportunity? It is in the sense that you know your delivery and the money you will make, but it's not in the sense that until delivery (or execution in the options case) you are still on the hook for the margins due from price fluctuations. Additionally you need to consider what ROI you will make from the trade. Even though it's ""guaranteed"" it may be less than what you can earn from other ""zero risk"" opportunities." "Defining parity as ""parity is the amount by which an option is in the money"", I'd say there may be an arbitrage opportunity. If there's a $50 strike on a stock valued at $60 that I can buy for less than $10, there's an opportunity.  Keep in mind, options often show high spreads, my example above might show a bid/ask of $9.75/$10.25, in which case the last trade of $9.50 should be ignored in favor of the actual ask price you'd pay.  Mispricing can exist, but in this day and age, is far less likely." In the equity world, if a stock trades at 110 and is going to pay a dividend of 10 in a few days, an option expiring after the ex date would take the dividend into account and would trade as if the stock were trading at 100. (Negative) interest rates may also lead to a similar effect. In the commodity world the cost of carry needs to be taken into account.
"Yes, almost always. I trade some of the most illiquid single stock options, and I would be absolutely murdered if I didn't try to work orders between the bid/ask.  When I say illiquid, I mean almost non-existent: ~50 monthly contracts on ALL contracts for a given underlying.  Spreads of 30% or more. The only time you shouldn't try to work an order, in my opinion, is when you think you need to trade immediately (rare), if implied volatility (IV) has moved to such a degree that the market makers (MM) won't hit your order while they're offering fair IV (they'll sometimes come down to meet you at their ""real"" price to get the exchange's liquidity rebate), or if the bid/ask spread is a penny. For illiquid single stock options, you need to be extremely mindful of implied and statistical volatility.  You can't just try to always put your order in the middle.  The MMs will play with the middle to get you to buy at higher IVs and sell at lower. The only way you can hope that an order working below the bid / above the ask will get filled is if a big player overwhelms the MMs' (who are lined up on the bid and ask) current orders and hits yours with one large order.  I've never seen this happen. The only other way is like you said: if the market moves against you, the orders in front of yours disappear, and someone hits your order, but I think that defeats the intent of your question." "It depends on the volatility of the underlying stock. But for ""normal"" levels of volatility, the real value of that option is probably $3.50! Rough estimates of the value of the option depending on volatility levels: Bottom line: unless this is a super volatile stock, it is trading at $3.50 for a reason. More generally: it is extremely rare to find obvious arbitrage opportunities in the market." No no no, the stock market is always going up, so OP just needs to lever up by writing a bunch of put options on the S&amp;P 500. I mean it hasn't had a serious drop in like a year, it's basically free money, right?  (But seriously, OP, 100% safe 4% returns are unrealistic unless you're an arbitrage genius). None of your options or strategies are ideal. Have you considered looking at the stock chart and making a decision? Is the price currently up-trending, or is it down-trending, or is it going sideways? As Knuckle Dragger mentions, you could just set a limit price order and if it does not hit by Friday you can just sell at whatever price on Friday. However, this could be very damaging if the price is currently down-trending. It may fall considerably by Friday. I think a better strategy would be to place a trailing stop loss order, say 5% from the current price. If the stock starts heading south you will be stopped out approximately 5% below the current price. However, if the price goes up, your trailing stop order will move up as well, always trailing 5% below the highest price reached. If the trailing stop has not been hit by Friday afternoon, you can sell at the current price. This way you will be protected on the downside (only approx. 5% below current price) and can potentially benefit from any short term upside. "Number 2 cannot occur. You can buy the call back and sell the stock, but the broker won't force that #2 choice. To trade options, you must have a margin account. No matter how high the stock goes, once ""in the money"" the option isn't going to rise faster, so your margin % is not an issue.  And your example is a bit troublesome to me. Why would a $120 strike call spike to $22 with only a month left? You've made the full $20 on the stock rise and given up any gain after that. That's all. The call owner may exercise at any time. Edit: @jaydles is right, there are circumstances where an option price can increase faster than the stock price. Options pricing generally follows the Black-Scholes model. Since the OP gave us the current stock price, option strike price, and time to expiration, and we know the risk free rate is <1%, you can use the calculator to change volatility. The number two scenario won't occur, however, because a covered call has no risk to the broker, they won't force you to buy the option back, and the option buyer has no motive to exercise it as the entire option value is time premium." "All margin is marked to market. Option longs do not post margin because long margin trading is forbidden. Equity longs must post margin if cash is borrowed to fund the purchase. Shorts of all kinds must post margin, and the rates are generally the same: a few standard deviations away from the mean daily change of the underlying. A currency futures trader, because of the involatility of most major monies, can get away with a few percentage points.  Commodities can get to around 10%.  Single equities are frequently around 20%, while indices can get back down to 10%. A future is a special case because both sides are technically short and long at the same time.  The easiest example to perceive is a currency future.  Which one is the buyer and which is the seller?  Both and neither. Contracts may be denominated for one side as the seller and the other the buyer, but contractually, legally, and effectively, both are liable to the other, and both must take delivery.  For non-currency assets, it only appears as if the cash seller is the buyer because cash is not considered an asset in the same way all other assets are, but the ""long"" is obligated to sell cash and buy the ""asset""." 1) Yes, both of your scenarios would lead to earning $10 on the transaction, at the strike date. If you purchased both of them (call it Scenario 3), you would make $20. 2) As to why this transaction may not be possible, consider the following: The Call and Put pricing you describe may not be available. What you have actually created is called 'arbitrage' - 2 identical assets can be bought and sold at different prices, leading to a zero-risk gain for the investor. In the real marketplace, if an option to buy asset X in January cost $90, would an option to sell asset X in January provide $110?  Without adding additional complexity about the features of asset x or the features of the options, buying a Call option is the same as selling a Put option [well, when selling a Put option you don't have the ability to choose whether the option is exercised, meaning buying options has value that selling options does not, but ignore that for a moment]. That means that you have arranged a marketplace where you would buy a Call option for only $90, but the seller of that same option would somehow receive $110.  For added clarity, consider the following: What if, in your example, the future price ended up being $200? Then, you could exercise your call option, buying a share for $90, selling it for $200, making $110 profit. You would not exercise your put option, making your total profit $110. Now consider: What if, in your example, the future price ended up being $10? You would buy for $10, exercise your put option and sell for $110, making a profit of $100. You would not exercise your call option, making your total profit $100. This highlights that if your initial assumptions existed, you would earn money (at least $20, and at most, unlimited based on a skyrocketing price compared to your $90 put option) regardless of the future price. Therefore such a scenario would not exist in the initial pricing of the options. Now perhaps there is an initial fee involved with the options, where the buyer or seller pays extra money up-front, regardless of the future price. That is a different scenario, and gets into the actual nature of options, where investors will arrange multiple simultaneous transactions in order to limit risk and retain reward within a certain band of future prices.  As pointed out by @Nick R, this fee would be very significant, for a call option which had a price set below the current price. Typically, options are sold 'out of the money' initially, which means that at the current share price (at the time the option is purchased), executing the option would lose you money. If you purchase an 'in the money' option, the transaction cost initially would by higher than any apparent gain you might have by immediately executing the option. For a more realistic Options example, assume that it costs $15 initially to buy either the Call option, or the Put option. In that case, after buying both options as listed in your scenarios you would earn a profit if the share price exceeded $120 [The $120 sale price less the $90 call option = $30, which is your total fee initially], or dropped below $80 [The $110 Put price less the $80 purchase price = $30]. This type of transaction implies that you expect the price to either swing up, or swing down, but not fall within the band between $80-$120. Perhaps you might do this if there was an upcoming election or other known event, which might be a failure or success, and you think the market has not properly accounted for either scenario in advance. I will leave further discussion on that topic [arranging options of different prices to create specific bands of profitability / loss] to another answer (or other questions which likely already exist on this site, or in fact, other resources), because it gets more complicated after that point, and is outside the root of your question. "You are right, if by ""a lot of time"" you mean a lot of occasions lasting a few milliseconds each. This is one of the oldest arbitrages in the book, and there's plenty of people constantly on the lookout for such situations, hence they are rare and don't last very long. Most of the time the relationship is satisfied to within the accuracy set by the bid-ask spread. What you write as an equality should actually be a set of inequalities.  Continuing with your example, suppose 1 GBP ~ 2 USD, where the market price to buy GBP (the offer) is $2.01 and to sell GBP (the bid) is $1.99.  Suppose further that 1 USD ~ 2 EUR, and the market price to buy USD is EUR2.01 and to sell USD is EUR1.99.  Then converting your GBP to EUR in this way requires selling for USD (receive $1.99), then sell the USD for EUR (receive EUR3.9601).  Going the other way, converting EUR to GBP, it will cost you EUR4.0401 to buy 1 GBP.  Hence, so long as the posted prices for direct conversion are within these bounds, there is no arbitrage."