The new net-price calculators required by Congress face several potential limitations, says a report issued on Monday by the federal Advisory Committee on Student Financial Assistance. The calculators, which colleges are required to have on their Web sites by the end of October, are designed to provide students and families with accurate, timely information about college costs and financial aid. Because the calculators will not be standardized, the report argues, prospective students may have a hard time comparing different colleges’ costs. The report also raises concerns that the calculators won’t be used by the neediest students, nor will they accurately compute merit aid. The advisory committee recommends that the higher-education community form a voluntary coalition to try to better “integrate and standardize” both net-price calculators and financial-aid-award letters.