Domestic

Effective for tickets issued on/after November 1, 2006:

Extensions to these validity polices are not permitted. Once any ticket expires, Northwest will retain all amounts collected from the traveler as an administrative service charge/cancellation fee.

Same-day travel changes—FlyNow option


International


* a cancellation is not considered a "change". You can cancel a ticket and use the credit later. When you re-book (use the credit) that is a "change".

Notes:
Any difference in fare when changing travel plans will be the responsibility of the traveler.
If the new itinerary has a higher fare, the fare difference will be collected along with the change fees.
If the new itinerary has a lower fare than the original ticket, the administration fee may be deducted from the difference in fares.
If there is excess value left after deducting the fee, then a credit voucher will be issued for the residual amount less any fees, which may be applied toward the purchase of future travel on Northwest.

NWA
Northwest Ailines Ticket Exchange Policies
Important
Domestic and international tickets have different exchange policies
With domestic tickets you have a year from the original departure date to exchange it.
With International tickets you have a year from the date of issue (purchase) to exchange it.