Kostovu se pripisuju zasluge za obnovu finansijske stabilnosti, provedbu dugo odlaganih ekonomskih reformi i privatizaciju više stotina državnih preduzeća, kao i za brz napredak Bugarske ka ulasku u EU i NATO.
Kostov is credited with restoring financial stability, implementing long-delayed economic reforms and the privatisation of hundreds of state-owned enterprises, as well as Bulgaria's speedy progress into the EU and NATO.