KLM's flight cancellation policy is quite comprehensive and varies depending on several factors such as the type of ticket, the time of cancellation, and the flight's origin and destination. Here's a detailed overview:

24-Hour Cancellation Policy for Flights to/from the US: If you book a flight through the US KLM website and cancel it within 24 hours, you're entitled to a full refund without any penalties or fees, irrespective of the ticket type​​.

Refundable vs. Non-Refundable Tickets: If you purchase a refundable ticket, you will receive a refund minus any cancellation fees. However, for non-refundable tickets, cancellation charges will apply​​.

Cancellation by the Airline: In cases where KLM cancels the flight, passengers have the option to choose either a new flight or a full refund. This refund should be processed to your bank account within 7 days, applicable mostly for flights to and from the EU​​.

Varied Refund Amounts: The amount refunded can vary depending on your route, travel class, and the specific type of ticket you hold. This implies that different passengers might receive different refund amounts based on these variables​​.