In 2026, "transferable" miles usually refers to two different things: alliance redemptions and point transfers. You generally cannot move miles from your Delta account to your United account. However, you can use Delta miles to book a flight on a partner like Air France because they are both in the SkyTeam alliance. The most flexible miles are those earned through credit cards (Chase, Amex, or Capital One), which can be transferred to various airline partners. There is also a small group of airlines, including British Airways, Qatar Airways, and Iberia, that use a shared currency called Avios, which can be moved freely between their respective accounts. For most other programs, "transferring" miles to a friend's account is possible but usually comes with a high fee that makes it a poor value.