Delta Airlines frequent fliers: you have just over two months to stock up on SkyMiles. Starting January 1, 2015, many passengers will need to fly over twice as much to earn the same number of award points.

That’s because Delta will award points in its SkyMiles frequent flier program based on fare paid instead of mileage flown, in a change announced back in February. Once the new system kicks in, lots of Delta passengers will find it impossible to earn anything close to the points they’ve been getting.

Let’s run the numbers. Say you’re flying round trip between New York JFK and Los Angeles International airports. Currently, a basic SkyMiles member (the least frequent flier, with no elite status) earns 4,922 mileage points for that trip based on flight miles. Top-status Diamond Medallion passengers (who fly more than 125,000 miles per year with the airline), receive those miles plus a 125 percent bonus, 11,075 miles total.

Up, up and away for old style frequent flier miles. (Photo credit: Wikipedia)

Come next year, awards will be based on the base fare, which doesn’t include taxes and fees. I just found an LAX-JFK round trip fare of $396. Subtract taxes and fees ($54) for a base fare of $342. A basic SkyMiles member will earn five times that, or 1,710 points. That’s about 35 percent of the current award miles.

More frequent fliers will earn more points per dollar, on a sliding scale up to 11 times the fare for Diamond Medallion passengers. That may sound like a lot, but 11 x $342 = 3,762 points, barely a third of the 11,075 they currently earn.

Yeah, ouch.

Some passengers will come out better, particularly those on short haul, relatively high fare flights. For example, passengers on Delta Shuttle service between New York and Boston currently earn a minimum of 500 miles, up to 1,125 for Diamond members. Next year, with a base fare of $207, a regular member would earn 1,035 points and a Diamond member 2,277.

None of this would be a big deal if Delta were changing its award redemption system commensurately, but that’s not happening. The number of SkyMiles points needed to redeem awards is remaining largely the same. On the other hand, Delta has announced that it’s getting rid of blackout dates. On the other other hand, no blackout dates don’t necessarily more award seats on any given flight.

Moral: you have until the end of this year to rack up the big flight miles.