American AAdvantage is offering up to a 30% bonus on purchased miles through December 31.
The most miles American allows you to buy in a calendar year is 60,000. This is a tiered bonus, and if you buy the full 60,000 miles you get 78,000 at a cost of $1808.75, or 2.32 cents per mile.
The miles are processed by Points.com so do not earn bonuses for your credit card spend. They don’t post instantly, usually 1-2 days but can take 72 hours under their terms, which is ok usually since American still generously allows 5 day award holds.
At the end of 2012 and again at the beginning of 2013 American offered a 50% bonus on purchased miles, which meant a price of 2 cents per mile instead of 2.3 cents.
If your need for the miles isn’t in the immediate term (although if your need isn’t immediate, I probably wouldn’t recommend buying miles), and you want to buy miles anyway, then see if you’re eligible for the US Airways 100% bonus on purchased miles which sells them at 1.88 cents per mile. Some time after American and US Airways merge, they’ll no doubt offer the ability to move points between Dividend Miles and AAdvantage accounts.