We all know options are derivatives, and their prices are derived from the underlying stock, index, or ETF. But with other factors at work such as implied volatility, time decay, etc. Have you ever wondered how can you know how much an option is going to move with respect to say the underlying? Very simple – check out its delta.
Delta is arguably the most heavily identifiable Greek (unless you count Socrates or Aristotle) especially by individuals learning to trade options. It offers a quick and relatively easy way to tell us what to expect from our option positions as we watch the price action of the underlying. Calls have positive deltas, as they typically move higher on a rise in the stock, and puts have negative deltas, as they typically move lower when the stock rises.
While some investors view delta as the percentage chance an option has of expiring in-the-money, it is really more of a way to project expected appreciation or depreciation. A delta of 0.50 for an AAPL call suggests the option should move 50 cents higher when the AAPL jumps a dollar, and lose 50 cents for every dollar loss in AAPL.
But delta is only foolproof when all other factors are held constant, which is rarely the case (and certainly never the case for time decay). If an option is moving more (or less) than its delta would suggest, it is likely because other variables are shifting. For example, buying demand might be pushing implied volatility higher, raising the price of the options. Still, this king of all Greeks is a good starting point for gauging how your options are likely to move.
Senior Options Instructor