Should I Buy United Miles?
Update: Some offers mentioned below are no longer available. View the current offers here.
TPG Twitter follower @MrBanilla16 tweeted me @thepointsguy about a United buy miles promotion he was targeted with:
"Should I buy united miles? I just got an email about it - 30% discount after I buy more than 10,000. Is it worth the price?"
Long story short, no, you should avoid buying miles when possible. Especially because right now, US Airways - another Star Alliance carrier - has a super lucrative 100% bonus on shared miles, which essentially creates new miles for about 1.1 cents apiece - less than half of what you'll pay to buy United miles (which will cost you 3.5 cents apiece plus a 7.5% excise tax).
US Airways also actually has a better award chart than United in many respects since certain redemptions provide an amazing value. Some examples include just 90,000 miles for roundtrip business class award tickets from North America to Asia, and 110,000 miles for roundrip business class award tickets from North America to the South Pacific (including Australia and New Zealand) and South Africa (which I actually took advantage of myself to fly South African Airways business class back in January), as well as some great off-peak award values.
Now, US Airways miles are definitely not as flexible as United's in many respects since you can only book roundtrip awards whereas you can book one-way awards with United, and once you start an award itinerary on US Airways you cannot make any changes to it, so you should have firm plans before you book your trip.
In general, if you can leverage those really lucrative buy or share miles promos, or even take advantage of the frequent 100% bonuses that another Star Alliance carrier, Avianca, has been offering over the past couple of years (though that can get a bit complicated in terms of redemptions), you can definitely get some better values than a mere 30% discount on United miles.
So I would recommend against this for you unless you have a very high-priced redemption that you know you can use these miles for or you just need a few to top up for a specific upcoming redemption - and remember, if you have one of the premium Chase cards that earn Ultimate Rewards points - including the Sapphire Preferred, Ink Plus and Ink Bold - you can always transfer those points to your United account instantly at a 1:1 ratio to top it up for an award.