Like many airlines, United doesn’t allow mileage upgrades on its lowest, “heavily discounted” Business Class fares (booking code Z). For that privilege you have to buy a D fare, which not only is sometimes hard to find, but also often not much less than full price (C fares).

So when I ran across these D fares recently, they caught my eye. Incidentally, upgrading from Business to First, especially on a low fare, is one of the best uses of your miles.

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