Through July 31, 2014, American is offering tiered bonuses on the purchase of AAdvantage miles, up to 30%. The tiered bonuses are as follows:
While you can purchase a maximum of 80,000 AAdvantage miles per calendar year (not including promotional bonus miles), the best value here is going to be purchasing exactly 55,000 miles. That’s because you get 16,500 bonus miles if you purchase 55,000-80,000 miles, so you’ll get the highest percent bonus with exactly 55,000 miles.
If you were to purchase 55,000 AAdvantage miles you’d get a total of 71,500 miles (including the 16,500 mile bonus) for a total of $1,961.56. That’s a cost of ~2.32 cents per AAdvantage miles.
Unless you’re in a bind or have a specific use in mind, this definitely isn’t a rate at which I’d speculatively pick up American miles. In April American ran a promotion whereby you could pick up miles for as little as ~2.15 cents per mile. Then back in February they had a promotion whereby you could purchase miles for as little as ~1.98 cents per mile.
With a specific short term use in mind it could still make sense to take advantage of this promotion, like if you can snag Cathay Pacific or Qantas first class award seats. Do keep in mind that American allows five day holds on AAdvantage award tickets, so you can always hold the award tickets, then purchase the miles, and then complete the purchase. Purchased AAdvantage miles don’t post instantly, so expect for it to take 2-3 days for purchased miles to post.
Also keep in mind that accounts have to be least 14 days old to take advantage of this promotion, and points purchases are processed by points.com, meaning they don’t qualify as airfare spend for the purposes of your credit card.
Ultimately I’d rather take advantage of a US Airways 100% bonus on purchased or shared miles, which would put the cost of miles more in the 1.67-1.88 cents per mile range. And even then I wouldn’t speculatively purchase miles. Keep in mind, though, that there are still some pretty substantial differences between American AAdvantage and US Airways Dividend Miles, so the miles really aren’t “created equal” (though one isn’t necessarily better than the other — it all depends on your individual needs).
Unless you have a very specific use in mind, this isn’t a promotion I would be taking advantage of.