0001321741 2026-06-01 2026-06-01 0001321741 us-gaap:CommonStockMember 2026-06-01 2026-06-01 0001321741 gain:A4875NotesDue2028Member 2026-06-01 2026-06-01 0001321741 gain:A7.875NotesDue2030Member 2026-06-01 2026-06-01 0001321741 gain:A7.125NotesDue2031Member 2026-06-01 2026-06-01 GLADSTONE INVESTMENT CORPORATION\DE false 0001321741 8-K 2026-06-01 DE 814-00704 83-0423116 1521 Westbranch Drive Suite 100 McLean VA 22102 (703) 287-5800 false false false false Common Stock, $0.001 par value per share GAIN NASDAQ 4.875% Notes due 2028 GAINZ NASDAQ 7.875% Notes due 2030 GAINI NASDAQ 7.125% Notes due 2031 GAING NASDAQ false