United Airlines is running a sale on miles right now that can be helpful if you need to redeem for an award. Actually, they are running two sales and they will use the lesser sale marketed to you if you find out you actually need more miles when redeeming. Here we go into this.
United is Running Two Sales – And Tries to Push The Worse Sale on You When Booking
Normally, it is not a great idea to purchase miles. The exceptions is when they are on sale (and you have some a use in the near future) or if you need to top up. Some airlines run better sales than others and United is normally not one of those.

This is the sale with the up to 95% bonus on purchased miles.

This is the price for the same amount of miles if purchased through the discount sale
Their current sales going on offer up to a 95% bonus on purchased miles. The 95% bonus threshold kicks in when you buy 45,000 miles. Below that, you get 70% bonus and below that 40% bonus.
The other sale going on is up to a 40% off purchased miles. That kicks in when you buy 50,000 miles or more. Below that it is 30% and then 20%.
Now, when you compare the two sales at a price per mile cost, here is what you get. The bonus sale (which United does not offer when it tells you that you need more miles) works out to costing 1.79 cents per mile. That isn’t terrible (and is actually almost as good as you get with United) and can have some practical purposes, even in economy. One such example is a one-way to/from Africa to the US (I’ve had family buy miles for just such a ticket as it saves them quite a bit over purchasing a ticket).
The other sale, the one with a percentage off the total price (and the sale that United gives you when you need to purchase more miles to book a ticket) comes out to 2.1 cents per mile at the 40% discount point.
Both sales run until May 30. If you have to buy miles, make sure you do it at the up to 95% bonus vs the link United gives you at checkout when you are coming up short.
It certainly would be nice if United presented both options to you – or at least the better one if they are only going to offer one. But, who really thinks an airline would do that? 🙂