If you’re sure you don’t want to rank any other schools if you’re a Finalist, and do apply ED, Northwestern says it looks at family need and not a dollar amount cutoff:
Northwestern is intentionally tying eligibility for its no-loan program to financial need, rather than to a certain level of family income, as many other schools have done. “We believe that linking our no-loan policy to financial need rather than family income is inherently more fair,” said Michael Mills, associate provost for enrollment management. “There are instances where middle- or even upper-middle-income families have tremendous financial need because of circumstances such as caring for a grandparent, coping with extensive medical expenses, enrolling several children in college simultaneously or other situations. Our new no-loan pledge based on financial need will help these types of families who otherwise wouldn’t qualify under an income-based program.”
Mills estimated that 80 percent of the beneficiaries of the no-loan program will come from families making less than $55,000 annually. The remainder would come from families with greater incomes but with financial circumstances such as those described above.
http://www.northwestern.edu/newscenter/stories/2008/01/noloanpolicy.html