The cost to upgrade to First Class on American Airlines after you have already purchased your ticket is highly variable and depends on real-time demand and seat availability. In 2026, American utilizes a "dynamic" upgrade offer system; you can often find a "paid upgrade" offer in the mobile app or on the website under "Manage Trips." For a domestic flight, these offers can range from $75 to over $500 per segment. For example, a short "hop" like Charlotte to Orlando might be offered for $95, while a transcontinental flight like JFK to LAX could be $400 or more. Alternatively, you can use AAdvantage miles to upgrade. A standard domestic "Miles + Copay" upgrade usually costs 15,000 miles plus a $75 fee. For international routes, a "Business to First" upgrade on partner airlines can cost up to 50,000 miles. It is important to note that "Basic Economy" tickets are often ineligible for these post-purchase upgrades unless you are an elite status member. If you see a low cash offer in the app, it is usually best to grab it immediately, as these offers are "perishable" and can disappear as the flight fills up.