canadiananalyst

Er... probably the easiest way to think about this is:

Call options are long the underlier. Deep in-the-money call options are like holding stock. So, deep ITM call options have delta = 1. Deep out-of-the-money call options probably won't pay off. So, the option price doesn't change much with the underlier price. Therefore, deep OTM call options have delta = 0. At-the-money is in between the previous two scenarios, so just say delta of ATM call options = 0.5.

For puts, it's the same but with negative signs for delta.

Anyway, try not to memorize this. If you understand the options, this should be intuitive.