Last Thursday, I arrived home to find a postcard in my mailbox advertising a United promotion offering up to 40% off purchased miles until June 20, 2013.

At these prices, I wouldn’t purchase tons of United miles speculatively, but if I were topping off my United MileagePlus account with a specific award redemption in mind, I could see myself taking advantage of this offer.

Here’s the skinny:

• Save 20% when you buy less than 25,000 award miles
• Save 40% when you buy 25,000 award miles or more
• These miles can only be used for awards and do not count toward Premier® status.
• A 7.5% federal excise tax applies.
• You can purchase up to 100,000 award miles per calendar year per account.
• A minimum purchase of 2,000 award miles per account is required for this offer.
• Miles are available in increments of 1,000 miles.
• Miles take 48 hours for miles to process and post to your MileagePlus account.
• Miles are nonrefundable.
• Promotional offer valid until 11:59 p.m. CT on June 30, 2013.

To participate in this offer or for more information, visit http://www.united.com/buymilesmailoffer