Via Ben, American Express is offering a bonus on transferring points over to Delta through the end of the year.

Registration is required, for every 50,000 points transferred you will receive a code later to apply to your Membership Rewards account to rebate 15,000 points. (No limit.)

Strictly speaking then, the offer is for a 30% rebate. Which means that you have to have available (or be able to borrow, or purchase) all of the points needed for the award you want to book through Delta Skymiles. A 30% rebate is mathematically equivalent to a 43% bonus.

Under this offer a net cost of 35,000 Amex points generates 50,000 Delta miles. A net cost of 70,000 Amex points generates 100,000 Delta miles, which is enough for a business class ticket on Europe and in my current experience Air France business class availability is really quite good. And not just on the Washington Dulles – Paris route where I often see as many as nine business class award seats available on a single flight, but on many routes, including West Coast (which make for good Alaska Airlines connections to the international gateway city, and Alaska is another Delta partner) and the Texas departures as well as New York.

There’s no reason to transfer points over to Delta speculatively hoping that you’ll be able to use them later. American Express is ‘live’ with Delta, meaning that transfers generally show up in your Delta account instantaneously. You can even set up a reservation on the phone with a Delta agent, and then transfer the points, the agent should see those points right away and be able to issue tickets. You’ll get 30% of your points back later!

Of course it’s important, then, to transfer in 50,000 point increments. Since other amounts are less efficient, it’s each block of 50,000 points that generates a 15,000 point rebate. (Transferring 90,000 points costs you a net 75,000 Amex points because you get one rebate. Transferring 100,000 points costs you a net 70,000 points since you get two rebates. You get 10,000 more Delta miles and are out of pocket 5000 fewer Amex points.)

If you have American Express Membership Rewards points, you should certainly register for this bonus even if you don’t think you’ll use it, it takes just a couple of seconds to do so and you don’t have to try to remember later if you find yourself making a transfer!

And you should consider reading my detailed discussion on making the best use of Delta miles, this may help highlight some of the uses of the miles and how to get them booked. I need to write up the step-by-step guide to searching for award availability, of course, and that’s certainly on my list. I have some ultra long-haul flying coming up, I’m hoping to be inspired to get some of those posts put together then.

I’d also note that for those of you earning American Express points via the Premier Rewards Gold card, the calculation here is really interesting — $23,334 in airfare spend generates 3 points per dollar or 70,000 points. That’s the net cost of a business class award ticket to Europe using this bonus offer. A truly amazing rebate on that airfare spend!

Of course you would need to have the full 100,000 points in your account to take advantage of the offer, though American Express will allow you to advance points that you haven’t earned yet, traditionally the allowed amount is 15,000 on most cards and 60,000 points on Platinum and Centurion cards. The nice thing about the points advance option here is that you’ll be receiving a rebate that will ‘pay back’ the points!

Personal Amex cards can also buy points at 2.5 cents apiece, which is less than most airlines sell their points for, purchases from American Express (and especially during a transfer bonus) can sometimes be an effective method of points purchase.

I’ll stress again — I believe this bonus only makes sense if you have a current use for Delta miles. It’s not even the best transfer bonus there’s been, and I’m not talking about the bonuses that mistakenly or accidentally were stacking where folks who hadn’t ever transferred points from American Express to Delta were getting 80% bonuses for a brief period before they shut it down. Over the summer American Express offered a 67% transfer bonus that was structured like this one, as a rebate. Obviously that was the better offer, it ended in September. It also suggests that this isn’t a ‘one of a kind’ offer, I think if you don’t have a reason to use Delta miles now it’s fine to wait, you’re not giving up a once in a lifetime opportunity for transfers. But if Delta awards do make sense for you now, this is definitely one to be on top of.