If your child has been accepted by one or more schools, you've probably received letters spelling out how much aid each college is willing to give.
"Spelling out" may be too generous a term, however. While financial aid letters are supposed to reveal your net cost—how much you would owe after any grants and scholarships—not all colleges follow the same format or provide the same information, notes Holly Morrow, a vice president of uAspire, a Boston-based nonprofit that advises students on financial aid. Colleges may omit some costs or list expensive parent loans as "aid."
To fairly compare offers, start with each school's total cost of attendance, then subtract only grants and scholarships to get your net price per year. Make sure you're accounting for all your expenses: not just tuition, fees, room, and board, but books, travel, laundry, and other living expenses. (One handy rule of thumb: The College Board says the average student spends about $4,200 a year on those extras.) If a college's aid letter isn't clear, call to get more details.
Consider, too, any major costs you might face that would exceed the averages. For example, if one college on your list is just down the road and another is way across the continent, figure you'll need to spring for some plane tickets if your child opts for the more distant school.
Don't stop there. "One of the worst things you can do is to focus solely on getting through the next year," advises Kal Chany, author of Paying for College Without Going Broke. Instead, try to estimate what it will cost to get your student from freshman orientation all the way to graduation.
For example, if your child was awarded merit aid for the first year, you can't assume that it will automatically continue. That may depend on maintaining a certain grade point average, often a 3.0. The average college student's GPA drops about 0.6 of a point after high school, according to research published by Columbia University, so even if your student had a B-plus average in high school, keeping it up might be difficult.
If your student is receiving need-based aid, you'll want to know how that could change in future years as well. For example, if you have another child who will be entering (or finishing) college before this one graduates, that could result in larger (or smaller) grants.
Arriving at a reasonable estimate won't be as simple as multiplying freshman-year costs by four. For one thing, assume colleges will raise prices by the recent average of 3% a year or so. Plus, many students no longer graduate in four years. The average now tops 4½ years, and lots of students take far longer than that.
Finally, some colleges are much better than others at helping their students graduate on time. You can get a sense of each school's track record by checking their four-, five-, and six-year graduation rates at CollegeResults.org. A college where your child will finish in four years may be less expensive in the long run than a seemingly cheaper school where you'd be writing checks for five years. MONEY's college rankings provide the net price of a degree for more than 700 schools, factoring in the average time it takes students there to graduate.