There are no rules of thumb for what families should pay for college, nothing akin to the principle of paying no more than 30 percent of your income toward housing. Those sorts of personal-finance maxims, while not hard and fast rules, give consumers and policymakers a framework for affordability. And that’s exactly what’s needed in higher education, according to the Lumina Foundation.

The education nonprofit released a paper Wednesday aiming to define college affordability in terms of what families can and should pay. It proposes that families pay for college with 10 percent of their discretionary income saved over 10 years and that students work 10 hours a week while in school.

This “Rule of 10” benchmark could be tailored to fit a family’s financial circumstances, said Zakiya Smith, Lumina’s strategy director. Families living below 200 percent of the poverty line, for instance, would not be expected to contribute savings or take on debt, though the student could still work. Assuming the student earned the federal minimum wage of $7.25 for 10 hours of work a week, that student could contribute $3,625 a year, or $14,500 over four years, according to the paper.

A family earning an average of $100,000 over 10 years might be able to contribute $51,500 based on the savings component of the rule. With the additional money the student earned from part-time work, that family could avoid having to take out loans to cover the cost of many public colleges.

But that’s assuming universities hold the line on the cost of attendance and government stakeholders increase investment in higher education. College prices, as the report notes, have ballooned by an average of 45 percent over the past decade, while household income has declined by 7 percent.

Asking families to adhere to the Rule of 10 could lead to what’s known as undermatching, when low-income students apply only to inexpensive colleges, even when their grades could gain them entrance into selective schools willing to foot the bill.

“Undermatching is very possible, given the gaps between a student’s affordability benchmark and the gaps in the actual financial award,” said Kevin Fudge, manager of government relations and community affairs at the nonprofit American Student Assistance. “The gap between the benchmark and the actual award will still be large, and the number of schools that have resources to fund fully high-need students shrinks each year.”

For the benchmark to be successful, Smith agreed there would need to be some substantial reforms in higher education. She said the benchmark could be used as the basis to develop policies that ensure families pay no more than they can actually afford. That may mean increasing federal grants and state subsidies or reducing college costs to achieve affordability.

“We’re not saying which one of those is the best approach to meeting the benchmark, just that there should be a benchmark,” Smith said. “You have to start with what the family can contribute and build around that.”

Lumina’s benchmark follows the rationale that everyone — parents, students, states and the federal government — has a role to play to make college affordable. It is the same rationale that anchors Hillary Rodham Clinton’s $350 billion higher-education plan, which also calls for students to contribute to the cost of their education with 10 hours a week of work.

Clinton — like Sen. Bernie Sanders (I-Vt.), one of her rivals for the Democratic presidential nomination — is also calling for the government to cover tuition at four-year public universities and community colleges, while former Maryland governor Martin O’Malley, another Democratic White House hopeful, wants to cap tuition at 10 percent of a state’s median income.

“What’s missing from a lot of the conversations is a clear outline of what should be expected from students and their families,” Smith said. “The ideal is for families to use this to gauge how much they should be saving . . . and for policymakers to structure postsecondary experiences that meet students’ needs.”

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