To "apply" for a 40% discount on Southwest Airlines in 2026, you must typically use a specific promotional code during a limited-time "System-wide Sale." Southwest frequently runs high-value promotions, such as their "Wanna Get Away Day" or "Wow" sales, where entering a code like SAVE40 in the "Promo Code" box on the booking page applies the discount to base fares. These discounts are usually restricted to Tuesday and Wednesday travel and require booking several weeks in advance. Additionally, you can "earn" deep discounts by utilizing the Southwest Companion Pass, which effectively gives you a 50% discount on every trip when traveling with a partner. For a peer-to-peer "win," ensure you are signed up for Click 'N Save emails; Southwest rarely offers "individual" applications for discounts, so staying informed about these flash sales is the only way to lock in that 40% reduction before the limited "discounted seat" buckets are sold out for your desired dates.