During the month of July, US Airways is offering up to a 50% bonus on one share miles transaction.

Offer valid for your FIRST Share transaction (purchaser or recipient) made between July 1, 2012 00:00:01 AM PT and July 31, 2012 23:59:59 PM PT. This bonus is only applicable for Share Miles and the offer does not apply to Buy or Gift Miles transactions. Bonus amounts will be awarded upon completion of the transaction. Bonus miles will be awarded to the recipient of the Share.

I interpret this as saying that you can only transfer points out of your account to generate a bonus once, and you can only receive a bonus once. It’s an open question whether you can do both with the same account, though a literally reading of the terms and conditions suggests that you cannot.

As always, an account needs to be open at least 12 days to share miles, and this costs 1 cent per mile plus 7.5% tax and a $30 processing fee.

That means sharing 50,000 miles costs $567.50. It generates a 25,000 mile bonus, and so each ‘new’ mile costs 2.27 cents when maxing out this promotion.

It’s a good opportunity, perhaps, to consolidate miles from little-used family member accounts that don’t have enough points to claim the rewards you want.

But it’s not the best way to buy miles from US Airways. Much of the year they tend to offer 100% bonuses on purchased miles that drops the cost per mile down to ~ 1.87 cents and thus is a better deal.

A couple of years ago, of course, when they ran a 100% bonus on shared miles, now that was amazing.