Which option allows the insured to purchase additional disability income protection at specific future dates?

The option that allows the insured to purchase additional disability income protection at specified future dates is known as guaranteed insurability. This feature is significant because it provides the insured with the ability to increase their coverage without needing to demonstrate insurability at the time of each purchase. This is particularly beneficial if the insured's health status changes, making it more difficult or costly to obtain additional coverage later.

Guaranteed insurability ensures that a policyholder can secure additional benefits as their needs grow, such as during career advancements or life changes, without the risk of being declined due to any new health issues that may arise. This option provides peace of mind, knowing that they have an avenue to increase protection as needed in the future, regardless of changes in their health situation.