You can't transfer airline miles from one airline to another. It's also impossible to combine two different types of miles into one account. However, you can use an airline's miles to book an award seat on another airline within the same alliance.

You cannot directly "convert" or transfer United MileagePlus miles into the frequent flyer program of another airline (e.g., you can't turn 10,000 United miles into 10,000 Delta miles). However, because United is a founding member of the Star Alliance, you can use your United miles to book flights on over 35 partner airlines directly through the United website. This includes major carriers like Lufthansa, Air Canada, ANA, and Singapore Airlines. Effectively, your miles are "universal" within that alliance. In 2026, United also allows "Miles Pooling," where you can combine miles with family members to reach a reward threshold faster. If you absolutely need the miles in a different non-partner program, you would have to use a third-party "miles broker" or "points exchange," which is generally not recommended as it offers terrible exchange rates and often violates the airline's terms of service.