You should keep the following in mind when you want to enter a calendar spread in trading options:

• You can sell an option that has a higher implied volatility of at least 15% than the option you are buying.

• Write options that have no more than 45 days left until they expire.

• Trade options that are within one strike price from the present underlying stock.

• Involve yourself with calendar spreads only when the relative volatility of the underlying stock is less than 6 (ideally 1 or 2).