Delta customers have long complained about reward availability at the 25,000-mile level, and its executives freely acknowledge that airline consumers in general should abandon any sense of expectations around this fixed price. “The 25,000-mile round-trip award fare that historically has been a standard for the airlines, I think you’re going to see that completely change,” Karen Zachary, who runs Delta’s SkyMiles program, told The Atlanta Journal-Constitution in May.

Ideally, you’d replace magic with math in the frequent-flier equation. But figuring out what a mile is worth requires knowing what flights will actually cost. And the only way to figure that out with Delta now is to try to actually book one in real time.

Image Delta does not post a chart showing how many miles a free ticket will require Credit... George Frey/Getty Images

Aside from the frequent travelers on the website FlyerTalk, which remains must-reading for consumers who want to do the math and decode the moves of Delta and other airlines, one of the carrier’s biggest critics in recent months has been Gary Leff. Mr. Leff has a day job working as a chief financial officer at a university research center, but he spends his spare time running a service that helps people redeem their miles and blogging about loyalty programs. He has posted about Delta repeatedly.

Delta does offer some free flights for less than 25,000 miles round-trip now. But Mr. Leff has done the math and has pointed out that the value you get per mile (when compared with the cash cost of the ticket) seems to rarely exceed two cents, an important figure that we’ll come back to shortly. Also, free flights in business class to Australia on Delta (long one of the magic redemption destinations for mile hoarders industrywide) now sometimes cost 830,000 miles per ticket, multiples of the former price.

The lack of clear predictable pricing irks Mr. Leff, even as it may help drive more people to his award-booking service. “I think Delta is not telling the truth, at a macro level, about the direction they’re taking the program,” he said. “And they’re making it harder for members to understand what their miles are worth.”

I tried to get a Delta spokesman, Anthony Black, to address Mr. Leff’s truthiness point squarely, but I failed to get much that was new other than a link to a list of low-cost redemption opportunities. Delta seems to think that no award chart should be necessary given that so many people redeem their miles for domestic tickets that only have a few different prices anyway. But if that’s the case, why not offer a permanent list of the range of possibilities for each market and explain what the rough odds are of actually getting the cheaper rates? Yes, consumers are used to unpredictable cash prices when they pay with their own money. But mileage programs were built on a different system of expectations, and people have saved those miles, often for years, accordingly.