The Treasury Bond Index (TBI Index) reflects the movement of the market for fixed-income securities, issued by the Bulgarian state. TBI Index serves simultaneously as a benchmark of the income from investments in similar securities, as it covers all issues of government securities (GS).

The weight of every issue in the index is determined on the basis of the issue market value (including accumulated interest) at the beginning of every month.
The calculation of the index value is done for each business day. The index is calculated on the basis of the overall income of the issues of government securities