By Beckie Supiano 

Rising tuition will be in the news this week with the College Board’s release on Thursday of its two signature reports.

“Trends in College Pricing” and “Trends in Student Aid” are packed with numbers, but if history is any guide, the one thing people will want to know is how much tuition and fees went up this year.

All right, all right, I’ll tell you. Average published tuition and fees rose 2.9 percent for in-state students at public four-year colleges, and 3.7 percent at private nonprofit four-years institutions. You can read the full reports here and explore individual colleges’ prices here.

But tuition is not the whole story. Consider this: The average list price of tuition and fees for in-state students at public four-year colleges in 2014-15 is $9,139. Room and board charges for the same students? Those come to $9,804.

Living expenses are an “under discussed” aspect of college affordability, says Zakiya Smith, a strategy director at the Lumina Foundation, who held a private convening of experts to talk about them earlier this fall. Ms. Smith has been pondering living expenses lately, partly because of the handful of new “free college” efforts designed to cover tuition and fees, but nothing more.

Whether and how living expenses should be considered part of the price of college is a matter of some debate. And when it comes to how colleges estimate what students will spend on room, board, and other expenses, and the implications of those estimates, things get really interesting.

Part of the Price Tag?

Everyone agrees that college students must live somewhere, eat something, and have other basic needs met. But is paying for those things part of paying for college?

States often design their financial-aid programs so that the money must go to tuition and fees rather than living expenses, says Debbie Cochrane, research director at the Institute for College Access and Success. The tendency is to trust institutions more than individuals. “There’s this sense,” she says, “if we give it to students, who knows how they’re going to spend it?”

Part of the issue is how students in different situations are typically perceived. “We’ve all heard people express concerns about people taking out loans to live or to pay rent,” Ms. Cochrane says. You don’t hear that when students borrow to live in their college’s dormitory or buy its meal plan.

“Trends in College Pricing” says many living expenses “are not really part of the cost of attending college, but are expenses people face whether or not they are in school.”

Even so, the report does examine them. Why? “Because students tend to think of living expenses as part of the cost of going to college, and because they must come up with the funds to cover these outlays, it is useful to use these expenses as a proxy for forgone earnings.”

In other words, the big expense of going to college is the opportunity cost. Hours spent studying and going to class are hours that can’t be spent working. The report doesn’t try to measure opportunity cost, instead using living expenses as an estimate of what that cost would be.

That approach avoids making “student” a special status. “While we have to make sure that we are supportive of students’ needs to meet their living costs while they’re in school, we have to think about this in the larger context of a society where lots of people face this, students and others,” says Sandy Baum, the report’s lead author.

And there could be unintended consequences of “creating the situation where the only chance is to be a student or otherwise they won’t have the money to live,” adds Ms. Baum, a senior fellow at the Urban Institute and research professor at the George Washington University Graduate School of Education and Human Development.

Public benefits are meant to help people who can’t afford to pay for food, housing, or other basic needs. But getting access to them can be challenging for students, says Amy Ellen Duke-Benfield, a senior policy analyst with the Center for Law and Social Policy. The center is running a pilot project in which community colleges work to help students get the benefits they are eligible for. But maintaining eligibility while enrolled is another issue.

Welfare, for instance, has a work requirement—one that federal law says can be fulfilled for 12 months by full-time postsecondary enrollment, Ms. Duke-Benfield explains. But only a handful of states allow recipients to meet their work requirements that way for more than 12 months. And even within that period, most states make students work at least 20 hours per week to stay eligible—a requirement that can slow or even stop their progress through college.

Whether the support comes from financial aid or public benefits, Ms. Duke-Benfield says, students need more resources. “If we’re serious about the completion agenda,” she says, “that means that we have to care about low-income students. And that means we have to deal with the fact there is an opportunity cost involved for them to go to college.”

That opportunity cost is often underestimated, says Sara Goldrick-Rab, a professor of educational-policy studies and sociology at the University of Wisconsin at Madison. Imagine a student who goes from working full time to working part time so he can attend college. Working part time doesn’t just mean working fewer hours. It also usually means lower hourly pay and, in many cases, unpredictable or inflexible hours.

“You experience more than a one-to-one loss for each hour,” she says. Paying for degrees students will be able to actually finish, Ms. Goldrick-Rab says, means supporting their living expenses.

Estimating Cost of Living

The financial-aid system is based on the understanding that students face expenses beyond tuition and fees. Colleges come up with a figure for their cost of attendance—the sum of tuition, fees, room, board, books, and more.

Cost of attendance is an estimate, one that matters for a couple of reasons. First, it is used to determine a student’s financial need (the expected family contribution, the amount that students and their families are deemed able to pay, is subtracted from the cost of attendance to determine need). Second, it’s used to determine a college’s net price as defined by the federal government—an increasingly important metric.

So how do colleges come up with the number? Rick Shipman, director of financial aid at Michigan State University, walked me through his system.

At Michigan State, the amount for “room” is the price of the average double room on the campus. “Board” is a meal plan that provides all-you-can-eat food during dining-hall hours. Mr. Shipman could elect to use different amounts for students who live off campus, but he does not. In East Lansing, Mich., he says, prices are comparable, on campus and off.

After adding tuition, fees, room and board, and books, it gets more complicated. “You get to decide as an institution which things you’re going to count and how to count them,” Mr. Shipman says.

For example, Michigan State’s cost of attendance includes money to cover a bus pass, but not to maintain a car, because there is a good public-transportation system in town.

It’s important that colleges help families understand the cost of attendance, Mr. Shipman says. They should know that the amount budgeted for books is just an estimate. And they could decide not to spend everything the college has included in the budget. “The degree to which you clarify what these things are helps them understand whether that’s something they want to borrow for,” Mr. Shipman says.

What families do with that information largely depends on their finances, Mr. Shipman says. High-income students may well bring a car to the campus and pay for off-campus parking. Lower-income students often work hard to keep their spending in line with the budget the college has come up with.

“It does change the bottom-line notion of what it costs to go to school,” Mr. Shipman says, “if $5,000 is spending money.”

Prices, of course, tend to rise. But increasing the budget for living expenses is no small matter for a college. Increases in tuition are typically paired with increases in financial aid. Increases in living expenses, though, are often simply absorbed by students. So in estimating those costs, colleges must find an amount large enough for students to live on but low enough that it won’t lead them to take on unnecessary debt.

“The reality is also that cost-of-attendance budgets are political,” Ms. Cochrane says. Low-balling living expenses makes a college look more affordable. That matters more now that net prices (the cost of attendance minus average grant aid) are gaining steam as a consumer tool and accountability metric.

Same City, Varying Expenses

It’s clear that different colleges interpret living expenses differently. A quick look at the costs of attendance that various colleges report to the government in the Integrated Postsecondary Education Data System shows a great deal of variation in what colleges in the same city budget for housing and food, particularly for students living off campus. The Association of Community College Trustees raised that issue in a letter to the Department of Education detailing its concerns about the proposed college-rating system.

“Until the department gets a grasp on how they adjudicate cost of living, they can’t use net price as the mechanism to be transparent,” says Jee Hang Lee, the association’s vice president for public policy and external relations.

In a recent paper, Ms. Goldrick-Rab and two co-authors examined the relationship between what colleges budget for living expenses and what data in the MIT Living Wage Calculator suggest it costs to live where those colleges are. The researchers found substantial gaps. Instead of allowing colleges to come up with their own cost-of-living budgets, those figures should be standardized, Ms. Goldrick-Rab says. Colleges could still adjust for unusual situations.

Financial-aid administrators are fond of the adage “live like a student now, so you don’t have to later.” But what that means—and how much help students get in making things work—depends on where they enroll.