Rating denote an issuer's ability to respond to adverse changes in circumstances and economic conditions. The rating scale is generally differentiated into various levels of credit viz., high investment grade, investment grade and speculative grade. The scale and corresponding definitions are as follows:
High Investment Grades
AAA Highest Safety
Debentures rated 'AAA' are judged to offer highest safety of timely payment of interest and principal. Though the circumstances providing this degree of safety are likely to change, such changes, as can be envisaged, are most unlikely to affect adversely the fundamentally strong position of such issues.
AA High Safety
Debentures rated 'AA' are judged to offer high safety of timely payment of interest and principal. They differ in safety from 'AAA' issues only marginally.
A Adequate Safety
Debentures rated 'A' are judged to offer adequate safety of timely payment of interest and principal; however, changes in circumstances can adversely affect such issues more than those in the higher rated categories.
BBB Moderate Safety
Debentures rated 'BBB' are judged to offer moderate safety of timely payment of interest and principal for the present; however, changing circumstances are more likely to lead to a weakened capacity to pay interest and to repay principal.
BB Inadequate Safety
Debentures rated 'BB' are judged to carry inadequate safety of timely payment of interest and principal; while they are less susceptible to default than other speculative grade debentures in the immediate future, the uncertainties that the issuer faces could lead to inadequate capacity to make timely interest and principal payments.
B High Risk
Debentures rated 'B' are judged to have greater susceptibility to default; while currently interest and principal payments are met, adverse business or economic conditions would lead to lack of ability or willingness to pay interest or principal.
C Substantial Risk
Debentures rated 'C' are judged to have factors present that make them vulnerable to default; timely payment of interest and principal is possible only if favorable circumstances continue.
D In Default
Debentures rated 'D' are in default and in arrears of interest or principal payments or are expected to default on maturity. Such debentures are extremely speculative and returns from these debentures may be realized only on reorganization or liquidation.