The federal government assists students and their parents in meeting the costs of postsecondary education through two student loan programs, the Federal Family Education Loan Program and the William D. Ford Direct Loan Program. Although the two programs provide similar benefits to borrowers, their structures and operations differ greatly. As a result, the federal government's cash flows for the two programs differ, as do its net budgetary costs when calculated as specified in the Federal Credit Reform Act. This Congressional Budget Office (CBO) paper--prepared at the request of the Senate Budget Committee--describes how the agency estimates the budgetary costs of the two student loan programs and what factors account for the differences in those costs. The following are appended: (1) Sample Subsidy Rates When a Borrower Defaults or Consolidates Loans; (2) Examples of Subsidy Calculated Using Fixed Interest Rates That Take Effect in 2006; (3) CBO's Estimates of Subsidy Rates for Various Types of Guaranteed and Direct Student Loans Made in 2006; and (4) Recent Legislative and Administrative Actions Affecting the Student Loan Programs. (Contains 11 tables, 2 boxes, and 29 footnotes.)