It's not a healthy apartment market until somebody is in some financial pain.

This might not be the textbook definition in neoclassical economics, but it sure is a good way to think about this famously cyclical business. If all the new buildings are getting fully leased, even the ones located well off the beaten path, that's a hot market possibly on its way to being overbuilt.

By this measure, the rental market around the University of Minnesota's main campus in Minneapolis is just becoming healthy.

The area has been one of the hottest targets for apartment builders with just under a thousand units opening for the 2014-2015 school year. Lately, leasing agents have had to offer gift cards or credits of perhaps $500 to entice would-be renters, the first signs of stress.

One of the new buildings, a couple of blocks east of the TCF Bank Stadium on the new light rail line, is called Metro Park East, and its owners told the financial newspaper Finance & Commerce that they hope to be three-quarters leased by the end of the year.

There's no real reason for the owners to panic, but it's certainly not what their competitors experienced over the last few years when units were filling up almost as soon as they were built.

But its relatively weak leasing doesn't mean the market is oversaturated. Perhaps, it was simply too many apartment units for this one lot, located two blocks behind the football stadium, a block off University Avenue and a good hike to Coffman Memorial Union in the heart of the campus.

Real estate developers — aided by their investors and lenders — do overbuild and overwhelm markets, of course. To be fair, however, it's not particularly easy to accurately forecast demand for a unique product two or three years after key decisions have to get made on whether to proceed.

Those who last a long time in the business need to have good sense of timing, knowing when to build and knowing when not to.

One of the first to know to build near the University of Minnesota's Minneapolis campus was Kelly Doran of Bloomington-based Doran Cos., breaking ground on Sydney Hall in 2009. His most recent and largest project, the Bridges, recently opened with 210 units near the Interstate 35W bridge just west of the main Minneapolis campus. He doesn't have any more projects planned.

Doran has built some awfully nice places for 19-year-old college kids to live compared with the squalor many of us may remember. The Bridges boasts an outdoor rooftop entertainment area, a movie theater, yoga studio, game room and 24-hour fitness center.

Doran attended the University of Minnesota, and explained that a transformation of who wants to go to college there is what created his opportunity.

"When I went to the U back in the late '70s and early '80s, if you could fog a mirror you could get in," Doran said. "Now it's a school of first choice. Now with its higher admission standards, when the kids go there, they want to have that college experience. They don't want to live at home."

When he was a student, about 25 percent of the students wanted to live near or on campus, Doran said, and he estimates the number in 2014 at roughly 60 percent. Considering the enrollment has grown since he was a student, Doran concluded that the market for near-campus housing tripled in just one generation.

Other factors contributed to making new development financially attractive, too — historically low borrowing costs on construction loans and an improvement in construction technology that allowed more floors to be built with relatively inexpensive wood-frame construction.

Other developers saw what Doran did, including locally based companies like Opus Development Co. and CPM Cos., and they jumped into the market.

"Now, has it gotten to be too much?" Doran said. "Yeah, it probably has."

This year, the new buildings struggled to fill all the units, and next year Minneapolis based CPM Cos. has two projects opening. The 202-unit Radius at 15th is close to the Golden Gopher football team's practice facility and the 333-unit WaHu project is under construction near TCF Bank Stadium on the eastern edge of the Minneapolis campus.

"In real estate, usually location wins out," said CPM co-founder Dan Oberpriller, looking ahead to the 2015 challenge of leasing these two properties. "We are comfortable in our locations."

A 66-unit project developed by a housing cooperative is also under construction, and then the pipeline of new apartment developments near the U's Minneapolis campus is finally dry.

"There's nothing behind us," Oberpriller said. "We would've heard of it by now. Maybe a triplex or something like that."

Curt Gunsbury built the 75-unit Solhaus and Solhaus Tower projects just down the street from CPM's big WaHu project, both this week more than 95 percent leased. Yet he's now working on a 30-unit condominium project, not more student housing.

He quickly added that he does not believe owners in the market are in for some serious financial pain.

Neither of the Solhaus buildings have only students as residents, a point he made several times about the deep pool of potential tenants. The university market lies in the heart of a big metro area, he said, along transit lines and adjacent to major freeways. There are cafes and entertainment venues within an easy walking distance. More than just undergraduates will want to live near these things.

For Gunsbury, what's coming in the university market is a lull in new construction rather than the end of the development cycle, which he doubts will ever really end anytime soon.

"It's an evolution of housing that's occurring there," he said. "And there's enormous pent-up demand for new housing stock."