The folks at Points.com brought an offer to my attention, which allows you to get double miles — free — when you transfer miles from one Delta SkyMiles account to another. But is it a good deal? Let’s do the math…

The maximum you can send from one account to another is 30,000. But there are fees attached: 1 cent per outgoing mile, plus a flat $30 charge per transaction. Those fees can add up.

But what if you send miles from one account in your family and then send the miles right back, effectively doubling the miles both ways? Churn it, baby! Would that take the edge off the fees?

Nope. You’ll still shell out some hefty coin if you want to double up those miles. Take a look:

Account 1 sends 15000 miles to Account 2. Account 2 receives 30000.
Account 1 balance is down 15000.
Account 2 balance is up 30000.
Cost to Account 1: $150 + $30 processing fee = $180

Account 2 sends 30000 miles to Account 1. Account 1 receives 60000.
Account 2 balance is back to even.
Account 1 balance is net up 45000.
Cost to Account 2: $300 + $30 processing fee = $330.
Cumulative cash outlay = $510.

So $510 gets you 45000 net miles, at a cost of 1.133 cents per mile. (If you both sent 30K miles to one another simultaneously, the cost would be slightly better… $660, or 1.1 cents per mile.) For me, that’s too much cash to spend, for too little payoff. The only — only !! — way I could endorse this is if you’re using the miles to get some hard-sought, expensive, premium class tickets to far-flung destinations. Only then might this be a good way to score some quickie miles.

Also, note that the base miles transfer within a week, but the double-mile bonus takes four to six weeks to post. So with only a few days left on the clock, you would have to have balances in each others’ accounts already. There are only 5 days left on this promo, after all. (Mea culpa. Had I noticed this when it came out in early October, you would have heard about it earlier…)

Finally, be aware that you can’t get the bonus miles if you open up a new account to transfer miles into. Read the bonus offer terms and conditions carefully:

Transaction must be completed on delta.com between October 1 and October 31, 2008. Bonus mile offer expires October 31, 2008. Bonus miles will be awarded for all transfer miles transactions made during this time period. Bonus miles will be awarded to the recipient of the miles. Offer does not apply to miles purchased under the SkyMiles Buy or Gift Miles program. The bonus is eligible only on transactions completed on delta.com. Bonus miles will be posted to the recipients account 4-6 weeks after the transfer transaction. Transfer Miles may only be donated and received by SkyMiles accounts that have been established for at least 60 days and have a Total Lifetime Balance greater than zero.

(Offer link)