Discussion of Delta, Continued:

If you own a call option that carries a delta of 70, that means that if the stock goes up by $1.00, your option will increase in value by $.70 (if the stock falls by $1.00, your option will fall by a little less than $.70).  Since each option is good for 100 shares, a price change of $.70 in the option means that the total value of your option has gained $70.

If a call option is deep in the money (i.e., at a strike price which is much lower than the stock price) and there are only a few days until it expires, the option is highly likely to finish in the money (i.e., at a higher price than the strike price).  If SPY is trading at $140 with a week to go until expiration, a 130 call option would naturally have a very high delta (approaching 100).  The stock would have to fall by $10 before it was no longer in the money, and that size move is unlikely in just a few days.

Owning a deep in-the-money call with only a few days until expiration is almost like owning the stock.  If the stock goes up by a dollar tomorrow, the option is likely to go up by that amount ($1.00, or $100 since the option is for 100 shares of stock).

On the other hand, if the 130 option had six months of remaining life, a lot can happen over those six months.  The delta value of the 130 call might be closer to 70 than it is to 100 since the stock is far more likely to fall by $10 if it has such a long time over which to change.  If the stock goes up tomorrow and you own a call with six months of remaining life, you can only expect your option to gain about $70 in value.

The opposite occurs when the option is out of the money.  At today’s option prices (which are a little lower than the historical mean average), with SPY at $140, the 143 call with one month of remaining life is 30.  Owning that call is the equivalent of owning 30 shares of stock.

If the 143 option had six months of remaining life, the delta would be 45 at today’s option prices.  The market is saying that there is a higher likelihood of that option finishing in the money since it has so many more months to fluctuate.  Owning a 143 call with six months of remaining life is like owning 45 shares of stock.