To determine if an airline promo code has expired, check its validity dates on the carrier's official website or deal-searching sites such as RetailMeNot and Coupons.com. If you enter a coupon code and no deduction appears in your fares, the coupon code is likely invalid or has already expired.
Airlines usually list the terms and conditions of their current promotions on their official websites, including the date by which fliers must purchase tickets and the time frame for outbound and inbound travel. Some airlines advertise discounts on sites such as RetailMeNot and Coupon.com for deals that do not require promotion codes. Click on the buttons next to advertised promotions to take advantage of these savings.