U.S. colleges have started, however reluctantly, to share more information about what students might actually pay to attend––the so-called net price. But the calculators that Congress has forced schools to provide since 2011 are often hard to find, vary widely in quality and should be used with some caution.

The idea behind the law was to give families a rough, individualized estimate of what college might cost them once scholarships and grants are deducted from the sticker price. (Loans are not supposed to be included in the net price figure since borrowing increases rather than decreases the cost of education.)

A realistic estimate of costs would give families much better information before a child applies. Previously they only got true cost information after the student was accepted and had been offered financial aid.

But many people, including parents and even high school counselors, are not aware the calculators exist, said college consultant Lynn O'Shaughnessy, who runs TheCollegeSolution.com website.

Some colleges do not seem eager to enlighten them, even though the U.S. Department of Education last year urged schools to post the tools prominently in logical places.

One quarter of the 50 colleges randomly selected by The Institute for College Access and Success, or Ticas, did not have links to their calculators on the financial aid or costs sections of their sites. Even when the calculator was on a relevant page, it was rarely posted prominently, the survey found.

Five of the 50 schools confused matters further by using some other name for the tool, such as "education cost calculator" or "tuition calculator."

The survey was conducted in 2012, but not much has changed, Ticas president Lauren Asher said last week.

To find New York University's calculator, for instance, users must click on three tabs - "Admissions," "Financial Aid and Scholarships" and finally "Financial Aid at NYU." At University of Pennsylvania, it takes four clicks to find the net price calculator, which is highlighted in a small blue box.

Harvard College, by contrast, posts its calculator on its financial aid home page, under the headline "You Can Afford Harvard."