It's hard to know exactly how much you've got to save for your kids' college educations because so much depends on where they plan to go.

But a new type of calculator is providing much better estimates of how much parents will be expected to pay, and what kind of financial aid a student might qualify for, based on family income and the school's tuition and housing costs.

A higher-education law Congress passed in 2008 requires all colleges to have net price calculators on their Web sites by 2011. They're already available at schools like Massachusetts Institute of Technology, Yale University, Princeton University, Amherst College and Williams College.

The calculators ask for much of the same financial information -- such as family income and assets -- as the government's Federal Student Aid program seeks on its Free Application for Federal Student Aid (FAFSA).

The calculator uses that information to determine how much each student will be expected to pay. (In college speak, that's the "Family Contribution.")

Then the calculator shows how much it costs to go to that school and the financial aid package the school might propose to make up the difference between the family's out-of-pocket contribution and the total bill.

In an example we ran using Amherst College's calculator, it estimated we'd have to pay $21,000 of the $53,000 it would cost to send a student there next year.

It proposed to make up the difference with a financial aid package that included a generous scholarship ($31,000) and campus job ($2,000).

The Massachusetts school was one of the first colleges to stop requiring student loans as part of its financial aid packages, so the "Student Loan" line showed up as "0."

But for most colleges and universities, student loans are a big part of financial aid packages.