In 2026, upgrading to United Polaris Business Class is most effectively done using PlusPoints or a MileagePlus Upgrade Award. If you have United Premier Platinum or 1K status, you receive PlusPoints that can be applied to "waitlist" for a business class seat. For everyone else, the best strategy is a "Miles + Cash" co-pay; you can request this upgrade in the United app anytime after booking, though the cost varies based on your original fare class. For 2026 travelers looking for a "guaranteed" deal, keep an eye on the "Day of Departure" (DOD) upgrades; within 24 hours of flight, United often offers "Buy Up" prices in the app that can be significantly cheaper than the original fare difference—sometimes as low as $499 for a transatlantic hop if seats are empty. Finally, you can use a Star Alliance Upgrade if you have miles with a partner like Lufthansa or ANA, provided the United flight is booked in a qualifying "premium" economy fare class.